Nuclear air handbook

This is important because replacement of highly contaminated HEPA filters may cost as much as 50c per cfm of installed capacity.” Often, when estimating filter replacement costs, only th

J

ERDA 76-21 Distribution Categories

UC-11, 70

NUCLEAR

AIR CLEANING

HIGH -EFFICIENCY AIR CLEAN IN G SYSTEMS

mi was prepared as an m o u n t of work

sponsored by the United S t a t u Covernrnent Neither the United Stater nor the United S t l t u Energy

Research and Dcvelopmnt Adminirtntion, nor Of

their employetr, nor any of their contractors

wbmnlncton or their employees makes any

w r n n t y cxpreu or implied, or assumes any l e d

liability i r responsibility for the aceuraey, cornplcteness

01 usefulness of any information, spparatlu product or pmeeu dirdorcd, 01 represents that its we wauld not

Contract No W - 7 4 0 5 - e ng - 2 6

OAK RIDGE NATIONAL LABORATORY

OPERATED BY U N I O N CARBIDE CORPORATION

'DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof The views and opinions of authors expressed herein

do not necessarily state or reflect those of the United States Government or any agency thereof

DISCLAIMER

Portions of this document may be illegible in electronic image products Images are produced from the best available original document

Fore word

to Second Edition

This handbook is a revision of ORNL/NSIC-65,

Design, Construction, and Testing of High-Efficiency

Air Filtration Systems for Nuclear Application,

which was issued in January 1970 For simplification,

the title has been shortened to Nuclear Air Cleaning

Handbook, and the report has been issued under an

ERDA number

The new edition updates the information of the

orginal volume, corrects some errors that appeared in

it, and adds some new material, particularly in the

areas of sand filters, deep-bed glass fiber filters, and

requirements for plutonium and reprocessing plants

Although A B Fuller was unable to contribute

directly to this edition, his earlier material on single-

filter installation and glove boxes has been largely

retained, though rewritten and updated With this

issue, J E Kahn of the Union Carbide Corporation

Nuclear Division’s (UCCND) Engineering staff joins

the writing team, contributing particularly in up-

dating the material on glove boxes and writing the

sections on sand filters and deep-bed glass fiber filters

in Chap 9 Others who have contributed to this

edition include J C Little, UCCND Engineering,

and a host of reviewers who provided technical

evaluation of the draft Particular thanks are due Dr

M W First of the Harvard University School of

Public Health, and Mr Humphrey Gilbert, consul-

tant to the Energy Research and Development

Administration (ERDA) and the Nuclear Regulatory

Commission (NRC) and former safety engineer with

the U.S Atomic Energy Commission, for their

detailed and thorough review of the complete draft

Others who reviewed the complete draft were J F

Fish, chairman of ANSI Committee N45-8; J C

Little, UCCND Engineering; J C Dempsey, ERDA

Division of Nuclear Fuel Cycle and Production; A B

Fuller, president of Fuller Engineering; and J T

Collins of NRC Thanks are also due to the members

of ANSI Committee N45-8 who, perhaps un- knowingly, supplied certain data and served as a sounding board for some of the concepts presented in the handbook We wish to thank the many vendors and ERDA contractors who supplied drawings and photographs used in the book We also acknowledge the work of Oak Ridge National Laboratory’s Technical Publications Department, particularly that of the Composition and Makeup groups, that of

R H Powell who provided editorial assistance, and especially that of P J Patton who edited and coordinated publication of this handbook

Reviewers who contributed in the technical review

of particular sections of the handbook include

R L Alley, American Warming and Ventilating

J E Beavers, Union Carbide Corporation Nuclear

R R Bellamy, Nuclear Regulatory Commission

R E Blanco, Oak Ridge National Laboratory

P J Breman, Union Carbide Corporation Nuclear

C L Cheever, Argonne National Laboratory

J C Elder, Los Alamos Scientific Laboratory

A G Evans, Savannah River Laboratory

S S Freeman, Mound Laboratory

R T Goulet, Cambridge Filter Corporation

R K Hilliard, Hanford Engineering Development

D J Keigher, Los Alamos Scientific Laboratory

C Lambert, Bechtel Power Corporation

F D Leckie, Nuclear Containment Systems, Inc

H A Lee, Atlantic Richfield Hanford Company

J Lipera, Lawrence Livermore Laboratory

R A Lorenz, Oak Ridge National Laboratory

Company Division

Division

Laboratory

W C Schimdt, Atlantic Richfield Hanford Com-

F R Schwartz, Jr., North American Carbon

Sheet Metal and Air Conditioning Coqtractors’

A A Weintraub, Energy Research and Develop-

C A Burchsted

Oak Ridge, Tennessee March 31, 1976

i v

Foreword

to First Edition

This handbook fills a large gap in the literature

concerning air cleaning and filtration, the gap that

encompasses design, construction, and testing of very

high-efficiency air cleaning systems The project was

originally conceived by Mr Humphrey Gilbert of the

USAEC and was sponsored by the Division of

Reactor Development and Technology of the

USAEC In preparing for the project we surveyed air-

cleaning systems at atomic energy facilities and

industrial installations throughout the United States

and Canada We visited AEC production reactors,

radiochemical plants, reactor fuel manufacturers,

clean rooms, equipment manufacturers, and one

chemical-biological warfare installation The pur-

poses of these visits were to review current practices

in high efficiency air cleaning and to define the

problems in operating, maintaining, and controlling

contamination release from very high-efficiency air-

cleaning systems from experienced people who were

dealing with such problems daily The handbook

reflects a consensus of our findings in these travels, in

addition to information gleaned from the available

literature

The handbook is addressed primarily to designers

and architectengineers We frequently observed a

lack of communication and feedback from people

with problems in the field to designers Our intention

is to bring to the attention of designers of future

systems the kind of problems that an operator faces and what he, the designer, must do to preclude or alleviate them We have purposely pointed out some poor practices in current design in addition to our recommendations in the hope that such practices will

go no further To give “do’s’’ without “don’ts” may encourage some designers to offer a poor design because he mistakenly believes that “it worked before.”

Those who have contributed to the handbook number literally in the hundreds and include those we consulted with and those who have given of their time

in reviewing drafts or have supplied specific bits and pieces of information We take this opportunity to thank the many friends we have made in the course of this project, particularly for their candidness in discussing problems and ways of solving those problems, and for their help in supplying photographs and information In particular we want

of the USAEC for their guidance, W B Cottrell of

ORNL for his help in getting the book published,

T F Davis of the USAEC‘s Division of Technical

I n f o r m a t i o n for his a s s i s t a n c e in indexing the material, J H Waggoner of ORNL for doing the illustrations, and Dr M W First of Harvard

University for his meticulous page-by-page review of the draft and suggestions for this final issue,

C A Burchsted

A B Fuller

Oak Ridge, Tennessee July 10, 1969

n

Preface

This handbook is another step in the continuing

effort of the Energy Research and Development

Administration to ensure the safe operation of

nuclear facilities Gaseous effluents from these

facilities are among the more difficult to control, and

the AEC, now ERDA, has long carried on an

intensive program aimed at their effective control

The record of this program is available in the

proceedings of the biennial AEC Air Cleaning

Conferences, the first of which was held in 1952 and

the fourteenth to be held this year in Idaho These

proceedings,and numerous technical reports issued

on this topic describe research, development, and

experience in sp’ecific facilities In most cases they d o

not provide general or coordinated guidance for the

designer

The purpose of this handbook is to draw on the

wealth of background data available, to digest and

evaluate it, and to provide guidance to the engineer and technologist in the design of future facilities The book is an update of the earlier ORNL/NSIC-65, issued through the Nuclear Safety Information Center a t Oak Ridge National Laboratory, and has been prepared under the direction of the ERDA Division of Nuclear Fuel Cycle and Production The previous edition has received worldwide recognition

as the authoritative text in the field of nuclear air cleaning system design We believe that publication

of this new edition by ERDA is a significant contribution to the technical literature

Frank P Baranowski, Director Division of Nuclear Fuel Cycle and Production, Energy Research and Development Administration

vi

Contents

FOREWORD TO SECOND EDITION

FOREWORD T O FIRST EDITION

1 INTRODUCTION 1

111

v PREFACE vii

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Background

Purpose and Scope

Design Considerations

Space Considerations

System Flexibility

Coordination of Design and Construction

Cost Considerations

Purpose of the Handbook

Glossary

1.9.1 Dictionary of Acronyms

1.9.2 Units of Measure and Metric Equivalents Used in This Handbook

1.9.3 Terms and Phrases

1 1 2 3 3 3 4 4 5 5 6 7 2 SYSTEM CONSIDERATIONS 12

Introduction

Environmental Considerations

2.2.1 Zoning

2.2.2 Airborne Particulates and Gases

2.2.3 Moisture

2.2.4 Heat and Hot Air

2.2.5 Corrosion

2.2.6 Vibration

Operational Considerations

2.3.1 Operating Mode

2.3.2 Filter Change Frequency

2.3.3 Building Supply Filters

2.3.4 Prefilters

2.3.5 Operation to High Pressure Drop

2.3.6 Underrating

2.3.7 Uniformity of Airflow

2.3.8 Maintainability, Testability

12

12

12

17

19

20

20

21

21

21

21

22

22

23

24

25

26

vii

2.4 System Configuration-Nomenclature

2.4.1 Component

2.4.2 Air Cleaning Unit

2.4.3 Air Cleaning System

2.4.4 Ventilation System

2.4.5 Filter or Adsorber Bank

2.4.6 Array

2.4.7 Air Cleaning Stage

2.4.8 Installed Capacity

2.4.9 Shgle-Component Air Cleaning Unit

2.4.10 Single-Path System

2.4.1 1 Parallel System

2.4.12 Segmented System

2.4.13 Redundant System

2.4.14 Branched System

2.4.15 Isolable Unit

2.4.16 Compartmented Unit

Emergency Considerations

2.5.1 Shock and Overpressure

2.5.2 Fire and Hot Air

2.5.3 Power and Equipment Outage

2.5.4 Air Cleaning System Layout Considerations

Multistage Filtration

2.6.1 Series Redundancy

2.6.2 Increased Decontamination Factor (DF)

2.5 2.6 28 28 29 29 29 29 29 29 29 29 29 29 29 29 29 31 31 33 34 34 37 37 38 2.7 Air Sampling 40

3 INTERNAL COMPONENTS

3.1 Introduction

3.2 HEPA Filters

3.2.1 Performance Characteristics

3.2.2 Construction

3.2.3 Weight of HEPA Filters

3 2 4 Mechanical Properties

3.2.5 Fire Resistance

3.2.6 Environmental Properties

3.2.7 Costs

Prefilters

3.3.1 Classification

3.3.2 Performance

3.3.3 Construction

3.3.4 Fire Resistance

3.3.5 Hot Air Resistance

3.3.6 Maintenance Considerations

3.3.7 Operational Considerations ?

3.3 42 42 42 42 44 46 46 48 48 50 50 50 50 51 53 53 54 54 3.4 Radioiodine Adsorbers 54

3.4.1 Introduction 54

3.4.2 Performance of Adsorption Systems 55

3.4.3 Adsorber Unit Design and Construction 58

3.4.4 Adsorbents 60

3.4.5 Inorganic Adsorbents 61

3.4.6 Adsorption System Design 62

3.5 Demisters 64

3.5.2 Demisters for Reactor Applications 65

3.5.1 Introduction 64

3.5.3 Performance 66

3.5.4 Normal Off-Gas Demisters for Radiochemical Service 69

4 HOUSING DESIGN AND LAYOUT 74

4.1 4.2 4.3 4.4 4.5 Introduction 74

Component Installation 75

HEPA Filter Adsorber Cell and Demister Mounting Frames

4.3.1 Structural Requirements 78

4.3.2 Mounting Frame Configuration 79

4.3.3 Frame Fabrication 81

4.3.4 Filter Clamping and Sealing 84

4.3.5 Filter Support 88

Size and Arrangement of Filter and Adsorber Banks 90

4.4.1 Vertical Filter Banks 90

4.4.2 Horizontal Filter Banks 92

4.4.4 Size of Banks 94

4.4.5 Arrangement of Banks 94

4.4.6 Floor Plan of Filter Banks 94

77 4.4.3 Location of Filters on Mounting Frame 92

Housings 95

4.5.1 General 95

4.5.2 Arrangement and Location 95

4.5.3 Steel Housings 98

4.5.4 Masonry and Concrete Housings 100

4.5.5 Seal Between Mounting Frame and Housing 101

4.5.6 Housing Floor 101

4.5.7 Housing Doors 102

4.5.8 Housing Drains 105

4.5.9 Housing Leaktightness 105

4.5.10 Other Housing Requirements 105

4.5.11 Paints and Coatings 106

5 EXTERNAL COMPONENTS 109

5.1 Introduction 109

5.2 Ductwork 109

5.2.1 Functional Design 109

5.2.2 Mechanical Design 109

5.2.3 Engineering Analysis 114

5.2.4 Materials of Construction 115

5.2.5 Paints and Protective Coatings 115

5.2.7 Acoustic Treatment of Duct 115

5.2.8 Duct Leakage 116

5.2.6 Hangers, Supports, and Anchors 115

ix

5.3 Dampers 116

5.3.1 Damper Specification 116

Description and Application of Dampers 117

Damper Design and Fabrication 117

5.3.4 Damper Operator 120

5.4 Fans 121

Fan and System Curves 121

Fan Performance-Systeh Effect 122

Multiple Fan Installation 124

5.4.4 Fan Capacity 125

Fan Reliability and Maintenance 125

5.4.6 Fan Installation 128

Location of Fan 129

Air Intakes and Stacks 130

5.5.1 General 130

5.5.2 S ~ c k s 130

Ventilation System Control and Instrumentation 131

5.6.2 Damper Control 131

Variable Inlet Vane Control 131

Variable Speed Control 133

5.6.5 Automatic Control 133

5.6.6 Central Control 134

6 SMALL AIR CLEANING UNITS 137

6.2 Housings 139

6.2.1 Component Installation 139

6.2.2 Housing Construction 142

6.2.3 Bagging 144

6.2.4 Housing Installation 144

Enclosed Filter Installation 146

Cylindrical Filter Elements 148

6.5 Instalktion 151

6.5.1 Human Factors 151

Fume Hood Filter Installations 151

Emergency and Portable Air Cleaning Units 154

7 GLOVE BOX FILTRATION 157

7.1 Introduction 157

Description of Glove Foxes 157

Importance of Glove Box Ventilation and Filtration 159

Design of Glove Box Ventilation Systems 159

Dilution of Evolved Gases 160

7.2.2 Heat Dissipation 160

Empirical Flow Rates 161

5.3.2 5.3.3 5.3.5 Qualification and Acceptance Testing 120 5.4.1 5.4.2 5.4.3 5.4.5 5.4.7

5.5 5.6

5.6.1 Introduction 131 5.6.3 5.6.4 5.6.7 Instrumentation 134

137 6.1 Introduction

6.3 6.4 6.5.2 6.5.3 7.1.1 7.1.2 7.2.1 7.2.3 7.2.4 7.2 Exhaust Requirements 161

n

X

7.2.5 Vacuum- and Pressure-Surge Relief 162

7.2.6 7.2.7 Exhaust Cleanup Requirements 163

Glove Box Exhaust Manifold : 163

7.3 Design of Filter Systems 164

7.3.1 Exhaust HEPA Filters 164

7.3.2 Exhaust Filter Located Inside the Glove Box 166

7.3.3 Exhaust Filter Located Outside the Glove Box 168

7.3.4 Inlet HEPA Filters 172

7.3.5 HEPA Filter Selection 173

7.3.6 Prefilters 173

7.4 Filter Replacement 174

7.5 Glove Box Safety 176

7.5.1 Protection Against Fire and Explosion 176

7.5.2 Protective Atmospheres-Inerting 180

7.5.3 Control and Instrumentation 181

7.5.4 DOP Testing of Glove Box Filters 184

7.5.5 Glove Box Shielding 185

8 TESTING 187

8.1 Introduction 187

8.2 Acceptance Tests 187

8.2.1 Duct and Housing Leak Tests 187

8.2.2 Mounting Frame Leak Tests 188

8.2.3 Airflow Capacity Test 188

8.2.4 Airflow Distribution Test-Adsorber Residence Time 188

8.2.5 Air-Test Agent Mixing Tests-Testability 189

8.3 Surveillance Testing 191

8.3.1 In-Place Testing for HEPA Filters 192

8.3.2 In-Place Testing for Adsorbers 194

8.3.3 8.3.4 8.3.5 Frequency of Testing 205

In-Place Testing for Multistage Systems 200

Adsorbent Sampling and Testing 203

8.4 Visual Inspection : 208

9 S P E C I A L - A P P L I C A T I O N R E Q U l R E M E N T S 210

9.1 9.2 9.3 Introduction 210

Remote Maintenance 210

9.2.2 Brookhaven Reactor Bypass Filter System : 211

9.2.3 Hanford Reactor Filter System 213

9.2.4 9.2.5 Savannah River Reactor Filter System 216

9.2.6 Remotely Maintainable Fish Filter System 218

9.2.7 Remotely Maintainable TURF Filter System 219

9.2.8 Remotely Maintainable HWESF Filter Assembly 220

9.2.9 Shielding 222

9.2.1 General Considerations 210

HFIR Filter System 216

Hot-Cell Filter Systems 221

xi

_

9.4 Natural Phenomena 223

9.4.1 Earthquake 223

9.4.2 Tornado 223

Fire and Smoke Protection 224

9.5.1 Operating Procedures 224

9.5.2 System Design 225

9.5.3 Fire Detection 228

9.5.4 Fire Control 229

Deep-Bed Sand Filters 231

Design of Deep-Bed Sand Filters 232

Plugging of Deep-Bed Sand Filters 235

Disposal of Spent Media 235

9.7.1 Introduction 236

Design and Operation 236

9.7.3 Wet Operation 239

9.7.4 Plugging 240

Disposal of Spent Filters 240

Reactor Engineered-Safety-Feature Air Cleaning Systems

9.8.2 Reactor Containment 241

High-Temperature Gas-Cooled Reactors 245

9.8.5 Liquid-Metal Fast-Breeder Reactors

Control Room Protection Air Cleaning Systems 246

Fuel Reprocessing Plant Air Cleaning 247

9.9.1 Introduction 247

Light Water Reactor Spent Fuel Reprocessing 248

LMFBR Spent Fuel Reprocessing 248

Near-Zero Release Concept 249

HTGR Spent Fuel Reprocessing Air Cleaning Systems 250

Sample Air Cleaning Equipment Specifications 254

Estimating Forms 269

Care and Handling of HEPA Filters 271

BIBLIOGRAPHY 278

9.5 9.6 9.6.1 9.6.2 9.6.3 9.7 Deep-Bed Glass-Fiber Filters 236

9.7.2 9.7.5 240 9.8.1 Introduction 240 9.8.3 Light W a t e r R e a c t o r s 244

9.8.4 245 9.8.6 9.8

9.9 9.9.2 9.9.3 9.9.4 9.9.5 9.9.6 Air Cleaning System Costs, Fuel Reprocessing 250

APPENDIX A APPENDIX B APPENDIX C APPENDIX D Seismic Design and Qualification of ESF Air Cleaning Systems 275

285

INDEX

xii

- _

1 Introduction

A nuclear air cleaning system is provided to protect

the public and plant operating personnel from

airborne radioactive particles and gases which are, or

could be, generated or released from operations

conducted in a nuclear reactor, fuel fabrication ‘or

processing plant, radiochemical operation, lab-

oratory, or other nuclear operation Such a sys-

tem is characterized by operation at very high con-

taminant collection levels, generally orders of

magnitude greater than those exhibited by air clean-

ing systems employed in commercial, industrial, or

pollution control applications The component

almost universally included in such systems is the

high-efficiency particulate air (HEPA) filter This

type of filter may be supplemented by common air

filters, bag filters, cyclones, scrubbers, or other

devices used in more conventional applications but is

nearly always employed in the nuclear air or gas

cleaning system as the final barrier between a

contained space (in which radioactive particulates

could be generated) and the point of release to the

atmosphere (i.e., the stack) or to an environmentally

controlled space of the facility

The prevention of even extremely low concen-

trations of airborne contamination is fundamental to

the safe operation of a nuclear facility.’ It is also an

important factor in the economic operation of such

facilities Although protection of the health and

safety of the public and of plant personnel’is the

primary consideration, the high costs of decon-

tamination and the possibility of shutdown of the

facility in the event of an accidental airborne release

of radioactive material are also important con-

siderations

Radioactive substances tend to deposit or ?plate

out” on ducts, components, and other exposed

surfaces and, in time, become sources of persistent

ionizing radiation This deposition can severely

complicate maintenance and operation of a , facility

_I 0

unless eliminated close to the source These problems are of particular concern in power reactors and fuel reprocessing facilities because of their potential for releasing large amounts of radioactive material in the event of a system malfunction or upset

1.2 PURPOSE AND SCOPE

Much of the information pertinent to the design, construction, and testing of very-high-efficiency air and gas cleaning systems for nuclear applications is contained in limited-distribution topical reports, technical papers, and job specifications that are often not readily available to designers Although there is a growing body of standards relating to the subject, the background information necessary for their effective interpretation is scattered The purposes of this handbook are to summarize available information in

a manner that is useful to the designer, to point out shortcomings in design and construction practice, and to provide guides and recommendations for the design of future systems The handbook summarizes findings from the literature and air cleaning practices

at laboratories, production facilities, power and research reactors, and radiochemical and fuel

recommendations presented reflect the experience of users and conditions that exist in operating systems where airborne radioactive material is being successfully controlled on a day-to-day basis, often in situations where personnel have had to live with, or adapt to, serious deficiencies in design or construc- tion

This ,handbook is limited to the mechanical or hardware phase of design Functional design-the sizing of a system or selection of components to meet the needs of a specific application-is beyond its scope The design of ventilation systems, of which the air cleaning systems are a part, is also beyond the scope of the handbook except as the ventilation

1

2

system design affects the operation and reliability of

the air cleaning facilities, or, conversely, as the air

cleaning facilities affect the operation and reliability

of the ventilation system The functional design of

nuclear air cleaning systems is covered in Safety

Monograph No 17 of the International Atomic

Energy Agency (IAEA),’ in various Regulatory

Guides of the Nuclear Regulatory Commission

(NRC),3-5 and in the ERDA Manual.(’ The functional

design of ventilating systems is covered in Industrial

Ventilation,’ the ASHRAE handbooks,‘ ANSI

not cover the theories of air filtration or gas

adsorption; however, discussions of air filtration

theory can be found in White’s and Smith’s High

Efliciency Air Filtration“ and Davies’ Air

Filtration;” gas adsorption theory of interest to the

nuclear industry is covered best in the proceedings of

the biennial AEC (now ERDA) Air Cleaning

Conferences

1.3 DESIGN CONSIDERATIONS

The design of nuclear air cleaning systems is

complicated by the extremely high collection efficien-

cies required t o meet the maximum permissible

concentration (MPC) values that have been es-

tablished for radioactive substances in air.’ In many

conventional situations (i.e., commercial, industrial,

and air pollution control), dust, chemical fumes, and

other contaminants can be detected by the human

senses before they reach concentrations that pose a

serious immediate threat t o health or safety The

situation is quite different in nuclear systems because

of the complete insensitivity of man t o the presence of

radioactivity, even at levels that represent an im-

mediate danger to life, and because of possible long-

term effects of exposures even at low levels The

lowest threshold limit values (TLV)” specified for

most chemical contaminants in air are a t least two

orders of magnitude higher than the M P C of any

radioactive material

The common air filters used in conventional air

cleaning applications are unable to decontaminate air

to the levels required t o meet these MPCs Even the

best of such filters exhibit number decontamination

factors (DF) no greater than 6 to 7 for submicron

particles (i.e., those having an aerodynamic diameter

of less than 1 pm), and the DF of most filters is 2 or

requisite MPCs for contaminants present as, or

adsorbed on, particulate matter, the HEPA filter

must be used By d e f i n i t i ~ n , ’ ~ this type of filter must have a minimum number efficiency’‘ of 99.97% for 0.3-pm particles; that is, a number decontamination factor of at least 3333 for all measurable particles, at any concentration, down to at least a 0.3-pm aerodynamic diameter Similarly, the iodine adsorp- tion units used in nuclear air and gas cleaning service must also exhibit collection (i.e., decontamination) efficiencies substantially greater than adsorption units used in fume and odor control and most toxic or noxious gas control applications For these com- ponents to function at their required performance levels, the manner in which they are installed, the connecting ductwork, and the ancillary components required to complete the air cleaning function must all meet standards of design and installation substan- tially higher than those which prevail in most nonnuclear situations That such high standards can

be met routinely and on a continuing basis is evidenced by the superlative safety record of most nuclear installations and by the control of releases to the atmosphere even under severe upset conditions

If airborne radioactive material is released from the system, there is the possibility of seriously contaminating occupied spaces of the plant, as occurred in the St Laurent fuel meltdown incident in France, or of contaminating the surrounding countryside, as occurred in the Windscale reactor incident in England several years ago Even a minor incident, in terms of the actual weight or volume of radioactive material released, could shut down a costly facility for an extended period of time The costs of decontamination can be thousands of times the losses due to such ordinary hazards as fire, explosions, or chemical spills, as illustrated below by the loss experience due to a small glove box accident

at an ERDA laboratory.”

$500

$76,200

Casualty loss due to explosion

Cost of cleanup and decontamination

In addition, the deposition and “plate out” of radioactive particulate matter and gases in and on ductwork, housings (Le., equipment casings), filters, and other air cleaning system components limits access, obstructs maintenance, and increases the cost

of operation The designer must appreciate these substantial differences between nuclear and conven- tional?: air cleaning systems Concentrations of radiotoxic materials in the air cannot be maintained below statutory limits’ if the design or layout of the system, or selection or installation of components, is

3

deficient Some operations in the past have relied to

some extent on dilution of airborne radioactive

wastes with large volumes of air, followed by

dispersal in the atmosphere This practice is no longer

acceptable in view of recent “as low as reasonably

emphasis must be placed on positive removal of

radioactive particulates, fumes, and gases by means

of well-designed and -maintained filtration and ad-

sorption systems

1.4 SPACE CONSIDERATIONS

The location and space allocations for exhaust and

air cleanup systems must receive close attention

beginning with the early stages of building planning

and layout and continuing through construction of

the facility Failure to provide adequate space for

ductwork in early building layouts often results in the

inability to achieve good aerodynamic design, in

excessive velocity and pressure losses that can com-

promise system operation, and in dynamic conditions

that can cause outleakage of contamination, even in

ductwork that operates under negative pressure

Poor location of filter housings, fans, and dampers

may limit their accessibility and thereby decrease

ability to maintain the system Also, since filters are

collectors of radioactive (or potentially radioactive)

dust, they can contain substantially greater concen-

trations of radioactive material than the air of the

contained space served by the system Changing

filters in open attics or crowded spaces of the building

increases risks at a time when risk is already higher

than normal Adequate access to and space surroun-

ding housings and filter installations decreases this

risk Space allotted for access to housings and

equipment must not be encroached upon forstorage,

field shops, or other operational conveniences during

the life of the facility

1.5 SYSTEM FLEXIBILITY

A shortcoming often encountered in ventilation

and air cleaning system designs is failure to an-

ticipate the possibility of future system modifica-

tion Although lack of ventilation system flexibility

may create no problems in nuclear reactors and other

facilities that have a fixed function, in radiochemical

operations and particularly in laboratories and ex-

perimental facilities where change is almost standard

procedure, provision for future system modification

at the time of original system design can pay for itself many times over The rebuilding of radioactively contaminated ducts and air cleaning systems is costly and hazardous, at best, and can be even more costly and hazardous when some provision for flexibility has not been left in the original design Because of the radioactivity problem, the costs of modifying or rebuilding a nuclear plant exhaust or air cleanup system may run five to ten times the cost of similar work carried out in a nonradioactive system Provi- sion for expansion of a system, including extra housing space, reserve fan and motor capacity, additional tie-on points, and sufficient mechanical joints in ductwork to permit reasonably easy dis- mantling, should be given serious consideration in initial planning

Temporary systems may not justify the extra

Nevertheless, the designer should keep in mind that temporary systems often become permanent or are adapted for other purposes Short cuts in design that make the modification of even a temporary system difficult can often become very costly to the owner in the long run

1.6 COORDINATION OF DESIGN AND CONSTRUCTION

The mechanical contractor cannot be expected to supply more than the minimum requirements shown

in the drawings and specifications He cannot be expected to build a system having the special features and requirements of a nuclear air cleaning system unless the design details and specifications clearly define them It is the functional designer’s respon- sibility to correctly interpret the owner’s needsand to develop clear and accurate system criteria It is the mechanical designer’s responsibility, in turn, to interpret these criteria and translate the functional design requirements into detailed equipment and construction drawings and specifications that can be followed by workmen with no experience in this specialty It is also the mechanical designer’s respon- sibility to ensure that the system, as it will be built, will meet the owner’s needs in terms of a safe, effective, reliable, maintainable, and economic system

An example of poor design and construction coordination occurred in a power reactor contain- ment purge system The facility designer, when allocating space for ventilation and air cleaning

4 n

equipment, allowed a nominal 144-in width for a six-

verification of this dimension was made by the

mechanical designer, and the drawings went to the

constructor who proceeded to pour concrete The

difficulty that developed is that a six-wide bank of 24-

by 24-in filters should be installed in a housing at

least 151 in wide (and preferably 158 in wide) to

provide room for a reliable filter mounting frame and

to provide ease of filter changing This type of error

should have been recognized in the mechanical design

stage To make matters worse, no embedments were

provided in the concrete to which the filter mounting

frame could be seal-welded This error resulted in a

filter installation that is, at best, questionable

It is also important for contractual relationships to

be carefully defined and enforced If the constructor

is to be responsible for correct performance of the

installed system, then test procedures, identification

of the parties who will make and evaluate test results,

and requirements for remedying errors and deficien-

cies must all be specified in the contract documents It

is not enough merely to require that the system meet

some minimum dioctyl phthalate (DOP) test effi-

ciency (usually 99.95%) If the system is to meet its

intended service requirements, technical require-

ments must be carefully followed during preparation,

review, and contractual acceptance of drawings and

specifications, a s well as during performance of the

work in the field

1.7 COST CONSIDERATIONS

Shortcuts and compromises with good design

practice result in unduly high operating costs

throughout the life of the system, as well as reduced

system reliability and performance A common error

in the planning and design of nuclear air cleaning

systems is to place too much emphasis on first (i.e.,

capital) costs Minimizing first costs often results in

high operating and maintenance costs if desirable

optional features are omitted or if sacrifices are made

in the amount or quality of space provided for

components, equipment, and ductwork During the

life of the system, operating and service costs usually

far exceed the first cost of building the system A

survey by the Harvard Air Cleaning Laboratory

showed that operation and maintenance accounted

for more than 85% of the total cost of owning a

nuclear air cleaning system, based on 20-year

amortization

Errors are sometimes made in choosing between alternate methods of accomplishing a desired objec-

tive because of the failure to consider all aspects of

cost When estimating capital costs of air cleaning systems, for example, the costs of special filter housings, dampers, fire protection facilities, clothing- change facilities, and other unusual (as compared with conventional air cleaning practice) provisions are often overlooked and may result in substantial avoidable maintenance costs for the sake of a few dollars’ savings in first costs For example, higher efficiency prefilters may greatly extend the life of the downstream HEPA filters and perhaps have longer life themselves, thereby increasing the time between filter changes This is important because replacement

of highly contaminated HEPA filters may cost as much as 50c per cfm of installed capacity.” Often, when estimating filter replacement costs, only the

“do” phase of the operation is considered, with little

or no heed given to the “make ready”and “putaway”

phases; yet these are generally the most time con- suming and costly phases of a filter change in a nuclear air cleaning system The time-consuming activities of clothing change, preinstallation inspec- tions, health physics monitoring, and decontamina- tion of the area and equipment after the change are often overlooked Other factors overlooked are escalations of labor and materials cost and the ability

to extend HEPA filter life by the selection of various combinations of prefilters, bank size, airflow rate, or other system parameters Appendix B provides a

form to assist the designer in estimating capital and operating costs and a form that breaks down a filter (or adsorber) change into at least its major elements

1.8 PURPOSE OF THE HANDBOOK

The information given in this handbook will supplement the designer’s previous knowledge and understanding of ventilation and air cleaning system design and construction by supplying background information on components and requirements for these very specialized applications Hopefully through the use of this handbook, the experienced functional designer will be better able to evaluate an owner’s requirements and to establish essential system criteria; the experienced mechanical designer will be better able to translate these criteria into effective system designs; and mechanical contractors will be provided with the knowledge needed to effectively carry out the intent of these designs to

5

provide safe, reliable systems at reasonable cost The

previous issue of the handbook'" has provided

background information for a growing family of

national standards covering air and gas cleaning

systems for nuclear applications; the new issue will

hopefully assist designers and engineers in using and

interpreting those standards It is also hoped that the

volume will provide a rationale for the engineer, the

manager, and the designer to justify the more costly,

but necessary, features that a nuclear air cleaning

American Concrete Institute

Atomic Energy Commission (see ERDA,

American Institute of Steel Construction

As low as reasonably achievable

Air Moving and Conditioning Associa-

tion

Aerodynamic mean diameter (of par-

ticles)

American National Standards Institute

ASHRAE American Society of Heating, Refriger-

ating and Air-conditioning Engineers

American Society of Mechanical En-

gineers

American Society for Testing and Ma-

terials

American Welding Society

Brunauer, Emmett, and Teller (test for

surface area of adsorbents)

Boiling water reactor

Chemical biological radiological (filter)

Continuous fire detector

CHd CFR

CG CRSI

cws

DBA DBS DBGF

D F DOP ERDA

ES ESF FRP GMA GTA HEP HEPA

HF HTGR HVAC

HWESF

IAEA IES

KI

Kr LOCA LMFBR LWR

M M D

MPC MPLd

MPLi

Methyl iodide Code of Federal Regulations Concentration guide

Concrete Reinforced Steel Institute Chemical Warfare Service

Design basis accident Deep-bed sand (filter) Deep-bed glass fiber (filter) Decontamination factor Dioctyl phthalate Energy Research and Development Ad- ministration

Equipment specification Engineered safety feature (system) Fiber-reinforced plastic

Gas metal arc (welding) Gas tungsten arc (welding) Hazard equivalent plutonium High-efficiency particulate air (filter) Hydrogen fluoride

High-temperature gascooled- reactor Heating, ventilating, and air con- ditioning

Hanford Waste Encapsulation and Storage Facility

International Atomic Energy Agency Institute of Environmental Sciences Potassium iodide

Krypton Loss-of-coolant accident Liquid-metal fast breeder reactor Light water reactor

Mass median diameter (of particles) Maximum permissible concentration Maximum permissible loading, desorp- tion

Maximum permissible loading, ignition

National Bureau of Standards

National Fire Protection Association

Number mean diameter (of particles)

Nuclear Regulatory Commission

Naval Research Laboratory

Nuclear Safety Information Center

Operating basis earthquake

Oak Ridge National Laboratory

or caulking compound)

SMACNA Sheet Metal and Air Conditioning

Contractors’ National Association

1.9.2 Units of Measure and Metric Equivalents Used in This Handbook

cfm fPm

ft

8

gal gPm

gr grift’

hr

Hz

in

in.wg in.’

Ib

m

P m

mCi pCi

mm

mR

millirem millirad PPm PSf psi rad rem scfm

S e C

tonne

cubic feet per minute x 0.000472 = m’/sec

meter micrometer millicuries microcuries minutes milliroentgen milliroentgen equivalent man millirad

parts per million pounds per sijtuare foot X 4.863 = kg/m’

pounds per square inch X 57.820 = g/cmz (unit of) radiation

roentgen equivalent man standard cubic feet per minute (see cfm) seconds

1000 kilograms

cubic meters per second meters per second meters

liters liters per second grams grams per cubic meter

centimeters kilopascals liters kilograms

kilograms per cubic meter grams per square centimeter

7

1.9.3 Terms and Phrases

absolute filter Obsolete term for HEPA filter

acceptance test A test made upon completion of

fabrication, installation, repair, or modification of

a system, unit, component or part to verify to the

user or owner that the item meets specified

requirements

activation analysis A method for identifying and

quantitatively measuring chemical elements in a

sample Atoms in the sample are first made

radioactive by bombardment with neutrons,

charged particles, or other nuclear radiation; they

then give off characteristic nuclear radiation by

which they can be identified and their relative

abundance can be determined

adsorber A device for removing gases or vapors

from air by means of preferential physical conden-

sation and retention of molecules on a solid

surface Adsorbers used in nuclear applications are

often impregnated with chemicals to increase their

activity for organic radioactive iodine compounds

adsorber cell A modular replaceable adsorber ele-

ment

AEC filter A HEPA filter with fiberglass medium

aerosol A dispersion of very small particles and/ or

droplets in air

air cleanup system A system provided t o decon-

taminate the air in, or exhausted from, a contained

space following a system upset o r prior to per-

sonnel access to the contained space

Obsolete term for HEPA filter

air-generated DOP See DOP

ALAP As low as practicable Obsolete term for

ALARA

ALARA As low as reasonably achievable The

design philosophy used to determine the need for,

or extent of, air cleaning and off-gas facilities,

based on their cost effectiveness in reducing

adverse impacts with respect to offsite and onsite

dose criteria Formerly known as ALAP.,

bag in, bag out A method of introducing and

removing items from a contaminated enclosure

that prevents the spread of contamination or

opening of the contaminated space t o the at-

mosphere through the use of plastic bagging

material

case, casing The frame or cell sides of a modular

filter element

clean-air device A clean bench, clean work station,

downflow module, or other equipment designed to control air cleanness (particle count) in a localized working area and incorporating, as a minimum, a HEPA filter and a fan

clean-air system An air cleaning system designed to

maintain a defined level of air cleanness, usually in terms of a permissible number of particles in a given size range, within an enclosed working area

clean room An occupied room designed to maintain

a defined level of air cleanness under operating conditions Inlet air is cleaned by HEPA filters

coating Paint or other protective surface treatment

applied by brushing, spraying, or dipping(does not include metallic plates)

contained space (contained volume) A building,

building space, room, cell, glove box, or other enclosed volume in which air supply and exhaust are controlled

containment (containment vessel or building) A

gastight enclosure around a nuclear reactor or other nuclear facility designed to prevent fission products from escaping to the atmosphere

contaminated exhaust system An air cleaning

system that is designed to remove harmful or potentially harmful particulates, mists, or gases from the air exhausted from contained space

contamination Any unwanted material in the air, in

process fluids, or on surfaces For the purposes of this handbook, contamination is usually assumed

to be radioactive

contamination zone An isolable area which is, or

which could become, contaminated and which is designed to facilitate decontamination

controlled area An area to which access is restricted

cover gas An inert gas, under pressure, provided in a contained space or process equipment item to prevent inleakage of air

criticality The state of sustaining a chain reaction, as

in a nuclear reactor When fissionable materials are handled or processed, they must be kept in a subcritical geometry, configuration, or mass to avoid accidental criticality

critical system, unit, or item One that is essential for

adequate or safe operation, failure of which would cause loss of function

CWS filter Chemical Warfare Service filter-a term

used for a HEPA filter with cellulose-asbestos

8

medium, kraft paper separators, and untreated

plywood casing Obsolete term for HEPA filter

backup protection against leakage through or failure of the first

decay heat The heat produced by radioactive

materials as nuclides spontaneously transform into

other nuclides or into different energy states Each

decay process has a definite half-life

decontamination The removal of unwanted sub-

stances from personnel, rooms, building surfaces,

equipment, etc

decontamination factor A measure of air cleaning

effectiveness; the ratio of the concentration of a

contaminant in the untreated air or gas to the

concentration in the treated air or gas

demister The preferred generic term for devices used

to remove entrained moisture from air (see

Thesaurus of Engineering and Scientific Terms)

Also a trademark of Otto H York Company

design basis accident (DBA) The most serious

accident that can be hypothesized from an adverse

combination of equipment malfunction, operating

errors, and other unforeseen causes

design pressure The pressure that is used for the

structural design of a unit, component, or system,

and which includes allowance for forces en-

countered under system upset conditions

double filtration An arrangement of two filters in

series with the second providing backup protection

against leakage or failure of the first Also a series

arrangement intended to increase the total filtra-

tion efficiency

DOP aerosol A dispersion of dioctyl phthalate

(DOP) droplets in air Monodisperse DOP is

generated by controlled vaporization and conden-

sation of liquid dioctyl phthalate to give a cloud of

droplets with diameters of approximately 0.3 pm

Polydisperse DOP is generated by blowing com-

pressed air through liquid dioctyl phthalate and

exhausting through special nozzles under con-

trolled conditions to produce a cloud of droplets

with a light-scattering mean diameter of ap-

proximately 0.7 pm

dry-type filter A filter having a medium that is not

coated with an oil or adhesive to improve its retention of large particles

enclosed filter A filter that is completely enclosed on

all sides and both faces except for reduced end connections or nipples for direct connection into a duct system Enclosed filters are installed in- dividually because there is a separate run of duct

to each filter unit

engineered safety feature (ESF) A unit or system that is provided to directly mitigate the conse- quences of a DBA

extended-medium filter A filter having a pleated

medium or a medium in the form of bags, socks, or

other shape to increase the surface area relative to the frontal area of the filter

face guard A screen, usually made from 4-mesh galvanized hardware cloth, permanently affixed to the face of a filter unit to protect it against damage caused by mishandling

face shield A screen or protective grille placed o v s a

filter unit after it is installed to protect it from

damage that might be caused from operations carried on in the vicinity of the filter

fail safe A design to give equipment the capability to

filter A device having a porous or fibrous medium

for removing suspended particles from air or gas that is passed through the medium

fail without producing an unsafe condition

filter bank A parallel arrangement of filters on a

common mounting frame enclosed within a single housing

final filter The last filter unit in a set of filters

arranged in series

functional design The establishment of airflow

rates, airflow capacities, types of components to be employed, general system layout, operational ob- jectives and criteria, decontamination factors and

dose The amount of ionizing radiation energy

absorbed per unit mass of irradiated material at a

rates, space allocations, and other overall features

of a system

specific location In the human body it is measured

in rems; in inanimate bodies it is measured in rads gas chromatograph An analytical instrument used

for quantitative analysis of extremely small quan-

double containment An arrangement of double

barriers in which the second barrier provides

tities of organic compounds whose operation is based upon the absorption and partitioning of a

I \ 9

gaseous phase within a column of granular

material

gas residence time The calculated time that a

contaminant or test agent theoretically remains in

contact with an adsorbent, based on active volume

of adsorbent and air or gas velocity through the

adsorber bed

glove box A sealed enclosure in which all handling

of items inside the box is carried out through long

rubber or neoprene gloves sealed to ports in the

walls of the enclosure The operator places his

hands and forearms in the gloves from the room

side of the box so that he is physically separated

from the glove box environment but is able to

manipulate items inside the box with relative

freedom while viewing the operation through a

window

HEPA filter Highefficiency particulate air

efficiency filter A throwaway extended-pleated-

medium dry-type filter with (1) a rigid casing

enclosing the full depth of the pleats, (2) a

minimum particle removal efficiency of 99.97% for

thermally generated monodisperse DOP smoke

particles with a diameter of 0.3 pm, and (3) a

maximum pressure drop of 1.0 in.wg when clean

and operated a t its rated airflow capacity

hot Highly radioactive

hot cell A heavily shielded enclosure in which

radioactive materials can be handled remotely with

manipulators and viewed through shielding win-

dows to limit danger to operating personnel

in-box Refers to an item within a glove box that can

be handled or manipulated only by means of the

box gloves or tools within the b o k

incell Refers to an item located within a cell or

enclosure that can be handled or manipulated only

by means of manipulators and/or a crane and

other tools within the cell

induct filter Refers to a single-filter arrangement in

which the filter unit is clamped between two

sections of duct or taped into a space between two

sections of duct

in-place test Penetration test of filter units or

charcoal adsorbers made after they are installed

inches of water A unit of pressure or pressure

differential (1 in.wg = 0.036 psi)

ionizing radiation Any radiation (alpha, beta, or

gamma) that directly or indirectly displaces elec- trons from the outer domains of atoms

isotope One of several forms or nuclides of the same chemical element that have the same number of protons in the nucleus and therefore have the same chemical properties, but have differing numbers of neutrons and differing nuclear properties

kidney system An air cleaning system that recir-

culates the air of a contained space

leaktightness The condition of a system, unit, or

component where leakage through its pressure boundary is less than a specified maximum value at

a specified pressure differential across the pressure boundary

maximum permissible dose The dose of ionizing

radiation which competent authorities have established as the maximum that can be absorbed without risk to human health

mechanical design Detailed design of a system

which results in exact layouts, equipment specifications, shop drawings, installation details and drawings, sizing and layout of ducts, housings and equipment, and other details necessary to achieve the objectives and meet criteria established

in functional design

medium (plural, media) The filtering material in a

filter

mounting frame The structure to which a filter unit

is clamped and sealed

normal off-gas The normal gaseous discharge from a

process or process equipment item

nuclear reactor An apparatus in which a chain

reaction of fissionable material is initiated and controlled

off-gas The gaseous effluent from a process or

operation

off-line system One that is not operating or is

normally held in standby

on-line system One that is operating or is normally

in operation, as opposed to an off-line system

open-face filter A filter with no restrictions over the

ends or faces of the unit, as opposed to the enclosed filter with reduced-size end connections

operating pressure The desired pressure correspond-

ing to any single condition of operation

10

overpressure Pressure in excess of the design or

operating pressure

particle, particulate A minute piece of solid matter

having measurable dimensions Also a radioactive

particle (alpha, beta) which can liberate ionizing

radiation or (neutron) which can initiate a nuclear

transformation

penetration The measure of the quantity of a test

agent that leaks through or around an qir cleaning

device when the device is tested with an agent of

known characteristics under specified conditions;

penetration is expressed as a percentage of the

concentration of the test agent in the space

upstream of the air cleaning device

poison Any material that tends to decrease the

effectiveness of an adsorbent by occupying adsorp-

tion sites on the surface of the adsorbent or by

reacting with the impregnants in the adsorbent

prefilter A filter unit installed ahead of another filter

unit to protect the second unit from high dust

concentrations or other environmental conditions

The prefilter usually has a lower efficiency for the

finest particles present in the aerosol than the filter

it protects (see roughing filter)

production test A test made on each item or a

sample of items or product from a production run

to verify that the item meets specification re-

quirements

PSU adsorber An adsorber that is permanently

installed in a system and that can be emptied of and

refilled with adsorbent without removing it from

the system

qualification test A test made on a product or

equipment item when it is proposed as a candidate

to meet certain service requirements, which will

verify to the user or owner that the item can meet

his requirements (see production test)

rad Radiation absorbed dose, the basic unit of

ionizing radiation One rad is equal to the absorp-

tion of 100 ergs of radiation energy per gram of

matter

radiation The propagation of energy through

matter or space in the form of electromagnetic

waves or fast-moving particles (alpha and beta

particles, neutrons, etc.) Gamma rays are elec-

tromagnetic radiation in which the energy is

propagated in “packets” called photons

radioactivity The spontaneous decay or disintegra-

tion of an unstable atomic nucleus accompanied by the emission of radiation

redundant unit or system An additional and in-

dependent unit or system which is capable of achieving the objectives of the basic system and is brought on-line in the event of failure of the basic system

rem Roentgen equivalent man The unit of ab-

sorbed radiation dose in rads multiplied by the relative biological effectiveness of the radiation

roughing filter A prefilter with high efficiency for

large particles and fibers but low efficiency for small particles; usually of the panel type

scrubber, A device in which the gas stream is brought

into contact with a liquid so that undesirable components in the gas stream are removed by reacting with or dissolving in the liquid

separators Corrugated paper or foil (usually

aluminum alloy or plastic) used to separate the folds of a pleated filter medium and to provide air channels between them

service environment The aggregate of conditions

(temperature, pressure, humidity, radioactivity, chemical contaminants, etc.) that surround or flow through a system, unit, or component while serving the conditions of design

shielding A mass of absorbing material placed

around a radioactive source to reduce ionizing radiation to levels not hazardous to personnel

shock overpressure The pressure intensity over and

above atmospheric or operating pressure produced

by a shock wave from an explosion, a suddenly closed damper, or other event

specific radioactivity Radioactivity per unit weight

spill Accidental release of radioactive or other

contaminating materials

split system A filter system consisting of two or

more trains operating in parallel; one or more of the trains may be on standby

of a material

standby system One held in reserve

surveillance test A test made periodically to es-

tablish the current condition of a system, unit, component, or part

11

system upset An accident, system malfunction, or

test program A formalized schedule of tests which

specifies the sequence of tests, the procedures to be

employed, and the acceptance criteria

train A set of components arranged in series In a

filter system this may be as simple as a damper,

HEPA filter, fan, and damper or as complex as a

damper, condenser, moisture separator, heater,

prefilter, HEPA filter, charcoal adsorber, another

charcoal adsorber, HEPA filter, fan, and damper

treatment The process of removing all or a part of

one or more chemical components, particulate

components, or radionuclides from an off-gas

stream

transient condition

I “Standards for Protection Against Radiation,” Code ./

Federal Regulations, Title IO, Part 20 (10 CFR 20)

2 Techniques f o r Controlling Air Pollution f r o m the Operation

OJ Nuclear Facilities, International Atomic Energy Agency,

Vienna, Safety Series No 17, 1966

3 Regulatory Guide 1.52, Design, Testing and Maintenance

Criteria for Atmosphere Cleanup System Air-Filtration and

Adsorption Units of Light- Water-Cooled Nuclear Power Plants,

U S Atomic Energy Commission, Washington, D.C., 1973

4 Regulatory Guide 3.12, General Design Guide f o r Ventila-

tion Systems of Plutonium Processing and Fuel Fabrication

Plants, U.S Atomic Energy Commission, Washington, D.C.,

1973

5 Regulatory Guide 1.32, General Design Guide f o r Ventila-

tion Systems f o r Fuel Reprocessing Plants, U S Atomic Energy

Commission, Washington, D.C., 1972

6 ER-DA @anual,-Appendix 6301, “General Design Criteria.”

7 Industrial Ventilation, American Conference of Governmen-

tal Industrial Hygienists, 13th ed., Lansing, Mich., 1974

book-Applications, American Society of Heating, Refriger-

ating and Air-conditioning Engineers, New York

9 ANSI 29.2, The Design and Operation of Local Exhaust

Systems, American National Standards Institute, New York, 197 I

IO P A F White and S E Smith, eds., High Efficiency Air

Filtration, Butterworth and Co., London and Washington, D.C.,

13 Number decontamination factor, DF, is the ratio of the

number concentration of particles in the unfiltered air to the number concentration in the filtered air Where no subscript is appended, decontamination factor in this handbook means number decontamination factor, as opposed to decontamination factor based on mass of particulate (DFm), intensity of radioactivi-

ty (DF,), or volume concentration (DF,)

14 E J Bauer et al., “The Use of Particle Counts For Filter

Evaluation,” A S H R A E Journal, American Society of Heating,

Refrigerating and Air-conditioning Engineers, October 1973, pp 53-59

15 IES CS-I, Standard f o r HEPA Filters, Institute o f

Environmental Sciences, Mt Prospect, Ill., current issue (Formerly American Association for Contamination Control.)

16 The efficiency of a HEPA filter is based on its absolute

particulate collection effectiveness; that is, the efficiency is relative

to the number of particles present (see Sect 3.2) The efficiency of

common air filters, on the other hand, is based on the mass concentration of particulate matter (see Table 2.4) or on the

staining effect of particulates on a reference surface, which is, of course, very subjective

17 “Hazardous Solvent Use Causes Explosion In Glove Box”

in Serious Accidents, U.S Atomic Energy Commission, Issue No

261, Feb 25, 1966

18 M W First and L Silverman, “Cost and Effectiveness of

Air-Cleaning Systems,” Nucl Saf 4( I), 61-66 (September 1962)

19 This cost includes $120 for the new filter, $150 or more for

handling and testing, and as much as $240 per filter for disposal

and retrievable storage

20 C A Burchsted and A B Fuller, Design, Construction, and

Testing of High-Efficiency Air Filtration Systems for Nuclear Application, USAEC Report ORNL/NSIC-65, Oak Ridge National Laboratory, January 1970

2 System Considerations 2.1 INTRODUCTION

A nuclear air cleaning installation is one of an

assemblage of interrelated and interactive parts that

include a ventilation system, the contained space

served by that system (Le., glove box, hot cell, room,

or building), and the processes carried out there The

design of an air cleaning installation has a direct

bearing on the performance and operating costs of

the ventilation system of which it is a part, and

equally, the design of the ventilation system directly

affects the performance and costs of the air cleaning

facility This chapter discusses, in general terms,

s o m e of the f a c t o r s that m u s t be c o n s i d e r e d w h e n

designing nuclear air cleaning facilities

2.2 ENYIRONMENTAL CONSIDERATIONS

The complexity of the air cleaning system needed

to provide satisfactory working conditions for per-

sonnel and to prevent the release of radioactive or

toxic substances to the atmosphere depends on the

nature of the contaminants to be removed (e.g.,

radioactivity, toxicity, corrosivity, particle size and

size distribution, particle shape, and viscidity); on

heat, moisture, and other conditions of the environ-

ment to be controlled; on the probability of an upset

or accident; and on the extent of hazard in the event

of such upset

2.2.1 Zoning

Workroom ventilation rates are based primarily on

cooling requirements, the potential combustion

hazard, and the potential inhalation hazard of

substances present in, or which could be released to,

the workroom Concentrations of radioactive gases

and aerosols in the air of occupied and occasionally

occupied areas should not exceed the concentration

guides (CG) established for occupationally exposed

persons under normal or abnormal operating con-

ditions, and releases to the atmosphere must not

exceed the permissible limits for nonoccupationally

exposed persons.”’ Because radioactive gases and aerosols might be released accidentally in the event of

an equipment failure, a spill, or system upset, the ventilation and air cleaning facilities must be design-

ed to maintain airborne radioactive material within prescribed limits, even following the worst con- ceivable accident that could occur in the plant.2 Control is made more difficult by the “as low as reasonably achievable” (ALARA) requirements which, at least for light water reactors, restrict gaseous and airborne particulate effluents to levels such that continuous exposure of persons in un- restricted spaces of the plant and its environs will not exceed the design objective annual dose limits set forth in Appendix I of 10 CFR 50.3 These guides limit annual dose to the whole body to 5 millirems, annual dose to the skin to 15 millirems, and annual radioiodine exposure to the thyroid to 15 millirems

In addition, the calculated air doses due to gamma and beta radiation should not exceed 10 and 20

millirads respectively These limits are design objec- tives and can be modified when rationalized by a cost- benefit analysis

Radioactive materials may be grouped as shown in Tables 2.1 and 2.2 with respect to relative inhalation hazard Quantities of radioactive materials greater than those indicated in Table 2.2 must be handled within a special containment, such as a hot cell or

glove box, which often has ventilation and/or exhaust facilities independent of those serving the building space in which the special containment is located The current CGs for radioactive substances

in air are specified in 10 CFR 20.’ A building or facility can be divided into confinement zones with respect to the hazard classes shown in Table 2.2 and based on the criteria shown in Table 2.3 The limits given in Table 2.3 are guides and should not be considered as absolute By introducing such indexes

of potential hazard and limitations on the quantities

of materials that can be handled, it is possible to establish a basis for ventilation and air cleaning

12

"Amount of radioactive material that can be handled without

special protection for personnel

requirements in various parts of a building or plant Figure 2.1 illustrates a typical zoning plan for a nuclear facility showing permitted occupancies, pressure differentials between zones required for proper ventilation and contaminant control, and zone assignments Not all of the zones listed in Table 2.3 would be required in all buildings, and an entire

building could quite possibly be designated as a single zone Zones are defined, with respect to function and permitted occupancy, as follows:

Table 2.2 Classification of isotopes according to relative radiotoxicity based on

inhalation hazard' amounts (Ci) equivalent to 1 g of Pu-239 (HEP)*

Italicized isotopes are fissile and require special consideration for nuclear safety

class 1 (Very high radiotoxicity)

Sr-90 + Y-90, Po-210, Po-210 + Bi-210, Ra-226, Th-228, U-232,

Np-236, Pu-238, Pu-239, Pu-240, Pu-241 Am-241, Am-242", Cm-242, Am-243, Cm-243 Cm-244, Cm-245 Cm-246

Np-237, Pu-242

Be-7, Na-24, S-35, K-42, Ca-47, S c 4 7 , Sc-48, Mn-52, Mn-54, Fe-55, Mn-56, Cu-64, Cia-72, As-74, As-76, As-77, Se-75, Br-82, Sr-85, Y-90, Nb-95, Mo-99, Pd-103 + Rd-103, Rh-105, Pd-109, A g - I l l , Cd-115, Sb-122, Te-127, Ba-131, La-140, (3-141, Pr-142, Pr-143, Nd-147, Ho-166, Sm-153, Ho-170, Lu-177, W-181, W-185, W-187, Re-183, Re-186, Os-191, Ir-190, Ir-192, Ir-194, Pt-191, Pt-193, Au-196, Au-198,

Au-199, Hg-197, TI-200, TI-201, TI-202, Ac-227, pure U-233,

H-3, C-14, F-18, C1-36, A-37, Cr-51, Ni-59, Ge-71, Kr-85, Tc-98, Tc-99, Ru-97, Rh-103, Te-129, 1-129, 1-132, Xe-133,

Pb-203, (1-235, U-236, natural thorium, U-238, natural uranium

.'.HEP = 2.16 X IO9 X 6 X IO-'' X 0.31 I

Therefore, 4.03 X IO-) Ci of Am-241 has the same hazard equivalent potential as I g of Pu-239

Source: Procedures and Practices f o r Radiation Protecrion, Health Physics Manual, Oak Ridge

Sample calculation-Determine curie H E P for Am-241

= 4.03 x IO-)

National Laboratory, Oak Ridge, Tenn

14

Table 2.3 Zoning of facilities based o n radiotoxicity of materials handled

Quantity of material handled vs radiotoxicity Radiotoxicity

Zone IV

0-1.0 pCi

"There is an upper limit to the quantity of transuranium elements which should be approved for glove box operations As a general rule, for those isotopes having a gram HEP index number below the

limiting quantity should be 100 mg (For example, 100 mg of Cm-244 generates the same hazard equivalent

potential as 4.3 kg of Pu-239.) Any operation involving more than 100 mg of such isotopes should be

conducted at facilities with more absolute containment features than are offered by glove boxes alone This

number may require further reduction due to penetrating radiation One gram of Cf-252, for example,

generates a dose rate of 2400 rems/ hr at a distance of 1 m in air

Source: Procedures and Practices for Radiation Protection, Health Physics Manual, Oak Ridge National Laboratory, Oak Ridge, Tenn

CELL SERVICE BAY (MAINTENANCE)

FUEL RECEIVING CELL ATM NITROGEN

INTERIM STORAGE HOT MAINTENANCE

Fig 2.1 Typical zoning plan for nuclear facility, showing type occupancy and operations permitted and static pressure that must be

maintained in each zone to prevent backflow of air t o areas of less contamination

15

Zone I: The interior of a hot cell, glove box, or

other containment for handling highly

features must prevent the spread of

radioactive material within and release

from the building under both normal

operating and upset conditions up to and

including the design basis accident

(DBA) for the facility Complete isola-

tion (physical separation) from

neighboring facilities, laboratories, shop

areas, and operating areas necessary

Entry forbidden until area is cleaned up

to Zone I1 classification Air-exhaust

system independent of those serving

surrounding areas required High ef-

ficiency filter, preferably HEPA type,

required in air inlet; two independently

testable stages of HEPA filters required

in exhaust Entry only with full-body

protective clothing and with respirators

or full-face gas masks, as specified by

health physicist

Zone 11: Glove box operating area, hot cell service

or maintenance area, or other building

space where high levels of radiation

could be present Particularly hazardous

operations conducted in chemical fume

hoods or glove boxes Sufficient air

supply t o produce inward airflow into

fume hoods or glove box ports (with

glove removed) of at least 100 lin fpm,

and may be 200 fpm for particularly

hazardous operations or if hot plates,

within such containment Air locks or

personnel clothing-change facility rec-

tinous monitoring of airborne radioac-

tive material required Personnel should

wear at least laboratory coats and

possibly shoe covers in glove box

operating areas, and full protective

clothing in service areas Respirators or

full-face gas masks should be available in

the event of an operational upset

Restricted access areas are generally

considered t o be Zone I1 hazard

classification

Zone 111: Hot cell operating areas, general

chemical laboratories, maintenance, and

other general working areas which are

usually “cold” but which are subject to low levels of radiation in the air Chemical fume hoods required for operations which could produce greater than CG for radioactive material or TLV for toxic or noxious material Operating

respiratory gear available for emergen-

monitoring required

Zone 1V: Office and “cold” shop areas No specific

protective clothing requirements Radia- tion monitoring may be required at exit points Bench-top operations permitted

in laboratories, but chemical fume hoods should be considered where airborne

stipulated in Table 2.1

Multizoned buildings are usually ventilated so that airflow is from the less contaminated zone to the more contaminated zone Recirculation within a zone, with the air circulated through a highefficiency air cleaning system before discharge back to the zone, might be permitted, but recirculation from a zone of higher contamination back to a zone of lesser contamination is prohibited The inside of exhaust and recirculating ductwork is considered to be of the same hazard classification as the zone it serves Airflow must be sufficient to provide the necessary degree of contaminant dilution and cooling and t o maintain sufficient pressure differentials between zones where there can be no backflow of air to spaces

of lower contamination, even under upset conditions

A pressure differential (4) of at least 0.1 in.wg between building zones is recommended, and sub- stantially higher differentials (0.3 to 1.0 in.wg) are

often specified between Zone I1 and Zone I spaces

The following criteria are specified at one of the ERDA national laboratories for the design and operation of radiochemical and laboratory facilities and for the buildings that contain them 4’5

Hot cells, caves, and canyons

Vacuum equal to or greater than 1 in.wg relative

to surrounding spaces shall be maintainedxall times to ensure a positive flow of air into the containment

Containment exhaust shall be at least 10% of cell volume per minute to minimize possible explosion hazards due to the presence of volatile solvents and to ensure that, in the event

/ 7

16

of cell pressurization due to an explosion, the

containment will be returned to normal

operating pressure (1 in.wg) in a minimum of

time

Maximum permissible leak rate shall be 1% of

cell volume per minute for unlined cells, and

0.1% of cell volume per minute for lined and

sealed cells at a Ap of 2 in.wg to ensure that the

escape of radioactive material will be minimized

in the event of cell pressurization; maximum

permissible leak rate of ductwork is 0.1% of

duct volume per minute a t Ap equal to 1.5 times

the static pressure of ductwork

4 Seals and doors shall withstand a Ap of at least

10 in.wg to ensure integrity of closures and

penetrations under all operating and design

basis upset conditions

5 The containment structure shall withstand the

DBA for that facility without structural damage

or loss of function

8

6 Operating procedures shall be designed to limit

quantities of flammable and smoke-producing

materials and solvents within limits that can be

accommodated by the ventilation system

without endangering functionability of the air

cleaning facility

Glove boxes

1 Vacuum shall be at least 0.3 in.wg between the

glove box and surrounding room

2 Exhaust rate is not specified but must be

adequate for heat load and dilution re-

quirements of operations conducted in the glove

box

3 Airflow shall be sufficient to provide at least 5

scfm to the glove box and to maintain an inward

velocity of at least 100 lin fpm through one open

glove port in every five glove boxes in the system

to ensure adequate inflow to prevent the escape

of contamination in the event of glove failure

4 Individual glove boxes shall be isolated or

isolable (under upset conditions) to prevent

spread of fire from one box to another

Chemical fume hoods

1 Vacuum shall be at least 0.1 in.wg between the

laboratory in which the fume hood is installed

and the corridor from which the laboratory is

entered

w

2 Exhaust rate of the fume hood shall be sufficient

to maintain sufficient airflow face velocity into the hood to prevent eduction of fumes from the hood to the room,even when the operator walks rapidly back and forth in front of, and close to, the hood face A face velocity of at least 100 lin fpm is recommended for operations with radioactive materials; 150 fpm is desirable

3 Each hood in the laboratory should be isolable

by means of dampers to prevent backflow through a hood when it is not in service

4 Each hood used for handling radioactive materials should have a HEPA filter in its exhaust duct, located close to the duct entrance

All hoods should, where practicable, exhaust to

a common stack

with no recirculation to the room (This require- ment may be reexamined in light of current energy conservation objectives; if a recir- culatory system is considered, the air cleaning system must be such that there is no possibility

of releasing radioactive or toxic particulates, fumes, or gases to the room, even under the worst foreseeable operating or accident con- ditions.)

Secondary containment structure or building

1 The building (structure) shall be designed to prevent the dispersal of airborne contamination

to the environment in the event of an accident in

a hot cell, glove box, fume hood, or building space

2 Under emergency conditions the building shall

be capable of being maintained at a vacuum of

at least 0.3 in.wg relative to the atmosphere For

increased reliability and simplicity, some buildings are held at this pressure under normal operating conditions; if this is not practicable, the ventilation system must be capable of reducing building static pressure to 0.3 in.wg in

20 sec or less All building air shall beexhausted through at least one stage of HEPA filters

During an emergency, the differential between Zone I spaces (glove boxes, hot cells) and other

building spaces must also be maintained

3 Airflow within the building must be from areas

of less contamination to areas of higher (or potentially higher) contamination

Air handling system

I Ventilation (recirculating or exhaust) and off-

gas systems shall be backed up by redundant air cleaning facilities (including filters and fans) to maintain containment in the event of fan breakdown, filter failure, power outage, or other operational upset Airflow shall always be from the less hazardous to the more hazardous area under both normal and upset conditions

2 Air exhausted from occupied or occasionally

occupied areas shall be passed through prefilters and at least one stage of HEPAfilters

Contaminated and potentially contaminated air exhausted from a hot cell, cave, canyon, glove box, or other primary containment structure or vessel shall be passed through at least two individually testable stages of HEPA filters in series, plus prefilters, adsorbers, scrubbers, or other air cleaning facilities as required by the particular application Air that is normally clean but has the potential of becoming con- taminated in the event of an operational upset (e.g., exhaust from a Zone I1 operating area) or during service operations when the zone is opened to a zone of higher contamination (e.g.,

a hot cell service area) and air from a poten- tially mildly contaminated space (e.g., Zone

111 area) require only one stage of HEPA filters

in the exhaust

3 Corrodents or moisture in the exhaust capable

filters (or other components, such as adsorbers) shall be removed or neutralized before they can reach components that can be affected

4 HEPA filters and adsorbers (where required)

shall be tested in place at a prescribed frequency (usually twice per year) HEPA filter stages shall exhibit a DF of no less than 3333 (99.97%

efficiency) as determined by an in-place test (see

Chap 8); because of the sensitivity of the test,

equivalent to the predelivery test efficiency of the filters (as determined by the manufacturer

or ERDA Quality Assurance Station); that is, a

DF of 10,000 for the in-place test may be

specified where filters having a predelivery test

are used in the system

Concentration limits for radioactive substances in air are specified in 10 CFR 20.’ Threshold limit values

(TLV) of toxic and noxious substances, including irritant and nuisance substances, are specified in Title

29 of the Code of Federal Regulations (Labor) but

are more conveniently tabulated by the American Conference of Governmental Industrial Hygienists in the annual issue of T L V S ~ The latter gives a procedure for determining TLVs for mixed toxicants and also gives limit values for heat stress, nonionizing radiation and noise

2.2.2 Airborne Particulates and Gases Although process-generated dust and particulate matter are the primary reason for installing exhaust

or air cleanup filters, a major portion of the dust and

particulate matter collected in those filters actually consists of atmospheric dust brought into the building with the supply air or by infiltration and of

“people-generated’’ particulates (e.g., lint, skin, and hair) These particulates contribute to degradation of the filters and sometimes become radioactive when exposed to certain operating environments (e.g., by adsorption of radioactive vapors or gases or by agglomeration with already radioactive particles) Because particles in the size range of 0.05 to 5 pm tend

to be retained by the lungs when inhaled, they are of primary concern in operations that involve radioac- tive material;’ they are also recognized as health hazards of nonradioactive air pollution.n As Table

2.4 shows, over 99% of the actual number of particles

present in atmospheric air falls in this size range Reports of dust concentration in air are generally based on the mass of particulate matter present As

Table 2.4 shows, mass accounts for only a negligible

portion of the total number of particles in the air This is important in filter selection because it indicates that some filters that have high efficiency based on weight may be inefficient on a true count basis That is, they are efficient for large particles but inefficient for small P0.75 pm) particles This is true

of most common air filters used as prefilters The HEPA filter, on the other hand, is highlyefficient for all particle sizes, down to and including the smallest shown in Table 2.4 The 99.97% minimum efficiency claimed for these filters is actually for the most penetrating size particles, those in the range from

0.07 to 0.3 pm Dust concentrations vary widelyfrom

place to place and, for the same location, from season

to season and from time to time during the same day Concentrations in the atmosphere may vary from as low as 0.01 grain per 1000 ft3 in rural areas to more

carbon

Smokes

F"tIWS

Table 2.4 Distribution of particles in typical urban air sample

Approximate Percent Percent Mean Particle size

(wn) ( W q per cubic foot of air weight count particle size range particle count by by

by

Rang

0-20 10-90 0-10 3-35 0-40

Source: From the Frank Chart, American Air Filter Co., Louisville, Ky

than 10 grains per 1000 ft3 in heavily industrialized

areas Dust-producing operations may generate con-

centrations as great as several thousand grains per

1000 ft3 at the work place Because the weight percent

determinations on which these concentrations are

based account for only a small fraction of the number

of particles present, the true count of particles smaller

than 5 p n may number in the billions per 1000 ft'

Atmospheric dust concentrations are usually lowest

during the summer months (June 1 to August 1)-as

much as 30% lower at that time than during the

remainder of the year.' Filter selection, particularly

prefilter selection and building supply filter selection,

must take into consideration the atmospheric dust

concentrations that can be encountered at the par-

ticular site at any time of the year

Figure 2.2 shows the distribution of particles (by

weight percent) in atmospheric air as a function of

particle shape Variations in particle shape, mean

particle size, particle size range, and concentration

affect filter life, maintenance costs, and operational

effectiveness The size range of various types of

particles, the technical nomenclature of various types

of aerosols, and the applicability of various types of

air cleaning devices as a function of particle size are

shown in Fig 2.3 A major source of the lint often

found on filters is derived from the abrasion of

clothing as people move about In addition, a person

at rest gives off more than 2.5 million particles (skin,

hair, etc;) and moisture droplets per minute, in the

size range of 0.3 pm to 1 pm.'" Process-generated

aerosols fall into two general size ranges Those

produced by machining, grinding, polishing, and

other mechanical operations are generally large,

probably from 1 pm to several hundred micrometers,

according to the nature of the process, and can be

removed effectively by common air filters or other

conventional air cleaning techniques The other class

includes those produced by evaporation/ condensa-

Spherical

e3

lrregul or

cubic Floker

STANFORD RESE.RCH lUSTlTUTE

HEPA filters, and adsorbents Where heavy concen-

trations of water mist or steam can be'expected,

under either normal or upset conditions, heaters,

demisters, or other means of reducing entrained

moisture to tolerable levels must be provided up-

stream of the filters to prevent plugging, deteriora-

tion, and reduced performance Condensation from

saturated air or gas streams and carry-over from air

washers and scrubbers are common sources of

sensible moisture When fire-protection sprinklers

are provided in operating areas or ducts, moisture

can be drawn into the filters if they are activated in the

event of a fire In nuclear reactors, large volumes of

steam and moisture would be expected in the very

unlikely event of a major loss-of-coolant accident or

heat-exchanger failure; this moisture can impair the

performance and integrity of HEPA filters and adsorbers unless removed before reaching those components

Condensation is particularly troublesome when filters are installed in underground pits, in housings located outdoors, or in unheated spaces of buildings Even when air entering ducts is above the dew point, duct walls, dampers, or filters may be cold enough to cause condensation on their surfaces Condensation can also take place in standby systems, particularly when groundwater can evaporate into the filter housing to condense on the walls, mounting frames,

or filters; salts that leach from wood filter casings can rapidly deteriorate aluminum separators In one instance, the separators of a bank of HEPA filters were nearly destroyed by this action in a three-month period Periodic ventilation of standby filters, on a

n

20

monthly or even weekly basis, is recommended to

prevent such occurrences

2.2.4 Heat and Hot Air

Continuous operation at high temperature

(>200° F) may be detrimental to both HEPA filters

and activated-carbon-filled adsorbers At high

temperatures, the shear strength of adhesives used in

the manufacture of HEPA filters and some prefilters

diminishes, thereby limiting the safe pressure drop to

which they can be subjected The limiting

temperature varies with the specific adhesive used

and should be checked with the filter manufacturer

where operation at elevated temperatures is

considered." Limiting temperatures for HEPA filters

are given in Chap 3 For continued operation at

temperatures in excess of 200"F, a specially con-

structed HEPA filter, in which the filter core is sealed'

into the steel case by means of a compressed mat of

glass fibers, is generally employed; however, tests

show that the efficiency of these filters, when

operating at high temperatures (about 800" F),

decreases substantially below the specified value of

99.97% minimum number efficiency for submicron

particles, even though the filters purportedly

operated within that specification value when tested

at room temperature before and after the high

temperature runs Apparently the steel case sides

expand away from the filter core, thus permitting

some degree of bypassing at high temperature Most

commercially available prefilters are not resistant to

heat, and special constructions must be specified if

continuous operating temperatures exceed 200" F

Ceramic-fiber filters having efficiencies as high as

80% for 0.3-pm particles are suitable for service at

temperatures up to 2000°F As with other types of

HEPA filters, however, DOP efficiency tests have

been made only at room temperature, and the actual

efficiency at high temperature is unknown Ceramic-

fiber filters are very expensive, extremely fragile, and

must be handled and installed with great care

The limiting temperature of adsorbents for cap-

turing radioactive iodine and iodine compounds is

related to the desorption temperature of the adsorbed

compound and of the impregnants with which the

material has been treated to enhance its adsorption of

organic radioiodides For triethylene diamine

temperature may be as low as 300 to 350°F

When temperatures higher than the operating

limits of air cleaning system components must be

12

accommodated, heat sinks, dilution with cooler air,

or some other means of cooling must be provided to reduce temperatures to levels that those components can tolerate Consideration must also be given to thermal expansion and heat resistance of ducts, dampers, filter housings, component mounting frames and clamping devices, and fans Considera- tion must also be given to flammability of dust collected in the ducts and on the filters

2.2.5 Corrosion

Many radiochemical operations generate acid or caustic fumes that can damage or destroy filters, other system components, and materials of construc- tion High levels of system performance and reliabili-

ty cannot be ensured when filters are exposed, even occasionally, to corrosive fumes unless corrosion- resistant HEPA filters, with specially treated media and separators and wood cases, and stainless steel ducts, housings, and mounting frames are employed

A new hydrogen fluoride resistant HEPA filter medium has been d e ~ e l o p e d ; ' ~ however, the material has not yet been produced commercially Although stainless steel filter cases have sometimes been employed for corrosion resistance, this is false economy because the life of standard case materials is nearly always greater than the life of the filter core

Stainless steel should not be specified for HEPAfilter separators because it makes the filter core impossible

to fabricate; separatorless filters, corrosion-resistant asbestos separators, or even plastic-coated aluminum separators are recommended

Stainless steel is recommended for ductwork and housings when corrosion can be expected Even this material may be insufficient in some cases, and coated (e.g., vinyl, epoxy) stainless steel or fiber- reinforced plastics may be necessary (corrosion- resistant coatings are covered by ANSI N5 12);14 plastics must be used with caution because they will soften and may collapse if exposed to high temperatures, as might be encountered during a fire

in the workroom

Scrubbers or air washers may be employed to pretreat the air or gas before it enters the final filters, but consideration must also be given to moisture carry-over if the scrubbers or airwashers are not designed and operated properly Demisters should be provided ahead of the filters Corrosion is always a danger but is not always obvious In activated- carbon-filled adsorbers, for example, even trace

amounts of NO2 or SO2 will concentrate in the

21

adsorbent over a period of time; in the presence of

moisture, they can form nitric or sulfuric acids that

are capable of corroding metal parts of the adsorber

In one instance, this sequence of events required

replacement of several hundred carbon-steel-cased

adsorber cells with stainless steel units, at a very

substantial cost Aluminum and carbon steel are

subject to corrosion when in contact with moisture-

laden carbon For this reason, stainless steel is always

recommended for adsorber cells and for adsorber-cell

mounting frames

2.2.6 Vibration

Vibration and pulsation can be produced in an air

or gas cleaning installation by turbulence generated

in poorly designed ducts, transitions, dampers, and

fan inlets and by improperly installed or balanced

fans and motors Apart from discomfort to per-

sonnel, excessive vibration or pulsation can result in

eventual mechanical damage to system components

when vibrational forces become high or when

accelerative forces (e.g., from an earthquake or

tornado) coincide with the resonant frequencies of

those components Weld cracks in ducts, housings,

and component mounting frames may be produced

by even low-level local vibration if sustained, and

vibrations or pulsations that produce no apparent

short-term effects may cause serious damage after

long duration

tions between the fan and ductwork are often employed, but these must be designed to resist the high static pressures often incurred in this class of system, particularly in those parts of the system which are under negative pressure Finally, the ductwork system must be balanced after installation, not only to ensure the desired airflows and resistances, but to “tune out” any objectionable noise

introduced during construction

- -_

Vibration produces noise that can range from

the unpleasant to the intolerable An important

factor in the prevention of excessive vibration and

noise is planning at the stage of initial building layout

and space allocation to ensure that adequate space is

provided for good aerodynamic design of ductwork

and fan connections Spatial conflicts with the

process and with piping, electrical, and architectural

requirements should also be resolved during early

design so that the compromises that are so often

made during construction, which lead to poor duct

layout and resultant noise and vibration, can be

avoided Ducts should be sized to avoid excessive

velocities while maintaining the necessary transport

velocities to prevent the settling out of particulate

matter during operation Fan vibration can be

minimized through the use of vibration isolators and

inertial mountings, although the use of these must be

balanced against seismic design requirements where

necessary (some designers prefer hard-mounting of

fans where continued operation during and after an

earthquake must be considered) Flexible connec-

2.3.2 Filter Change Frequency

The principal costs in operating a highefficiency air cleaning system are power (i.e., for fans), replace- ment filters and adsorbers, and labor The principal factor that affects these costs is the frequency of

Many facilities require standby exhaust or air cleanup systems that are operated only in the event of

an emergency or redundant air cleaning facilities that are brought into operation when a parallel on- line facility is shut down because of failure or for maintenance When designing stand by systems, the engineer must keep in mind the possibility of corrosion and filter and adsorber deterioration even when the system is not in use

22

changing filters (adsorbers) Replacement filters and

adsorbers and labor costs may make up as much as

70% of the total cost of owning a system (including

capital costs) over a 20-year period Power accounted

for only 15% of the total owning costs in a study made

by the Harvard Air Cleaning Laboratory Measures

such as the use of high-efficiency building supply-air

filters, the use of prefilters ahead of HEPA filters,

operation of the system below its, rated airflow

capacity, and operation of HEPA filters until they

have reached high airflow resistance before replace-

ment all tend to decrease filter change frequency and

thereby reduce costs These factors are discussed in

the following sections

2.3.3 Building Supply-Air Filters

Atmospheric dust brought into the building with

ventilation air constitutes a substantial fraction of the

dirt load in the building and the dust load in the

exhaust air cleaning system Removal of this dust

before it gets inside the building has the double

advantage of protecting the exhaust filters from

premature dust loading and of reducing janitorial

and building maintenance costs When operations

within a building d o not generate heavy concen-

trations of smoke, dust, or lint, it may be possible, by

providing medium-efficiency (50 to 65% ASHRAE

efficiency)16 building supply-air filters, to substantial-

ly reduce the dust loading in the exhaust system,

thereby shifting much of the burden of what would

otherwise be a change of “hot” (radioactive) prefilters

in the exhaust system to a more economical change of

“cold” supply-air filters The labor costs involved in

replacing “cold” filters is a small fraction of those for

replacing “hot” filters

Noticeable reductions in janitorial costs have been

observed in several ERDA installations after chang-

ing to higher efficiency building supply-air filters

There is also a trend toward using better building

supply-air filters in commercial buildings; one

operator of a commercial office building reported

that the time interval between major cleaning and

repainting had doubled after replacing his original

efficiency filters.”

Louvers or moisture separators e r both must be

provided at the air inlet to protect the supply filters

from the weather Rain, sleet, snow, and ice can

damage or plug building supply-air filters, resulting

not only in increased operating costs but upset of

pressure conditions within the building and possible

impairment of the more critical exhaust air cleaning system Heaters are desirable in the building supply system, even in warm climates Icing has caused severe damage to building supply-air filters at a number of ERDA installations, even in the South Screens should be provided over supply-air inlets located at ground or roof level to protect inlet filters and demisters from grass clippings, leaves, dirt, and windblown trash If possible, inlets should be located well above grade or adjacent roofs so they are not burdened by such materials, preferably at the second- floor level (or equivalent height above an adjacent roof) or higher

2.3.4 Prefilters

HEPA filters are intended primarily for removal of submicron particles and should not be used as coarse- dust collectors They have relatively low dust-holding capacity, particularly for large particles and lint, and may plug rapidly when exposed to high concen- trations of such material or smoke; lint may tend

to bridge the pleats of the filter, even further reducing its capacity The HEPA filter is also the most critical particulate-removal element in the air cleaning system from the standpoint of preserving contain- ment, and its failure will result in a failure of system function Prefilters, installed either locally at the entrances to intake ducts, in the central exhaust filter house, or both, extend the life of HEPA filters and provide at least a measure of protection against damage Local ductentrance filters also minimize dust accumulation in ducts and reduce an otherwise potential fire hazard A typical increase in HEPA filter life through the use of prefilters is illustrated in

Fig 2.4 The increase for a specific application is, of

course, dependent on the quality of the prefilter selected and the nature and concentration of dusts and particulate matter in the system

Generally, prefilters should be provided when the potential dust concentration in the air leading to the air cleaning system exceeds 10 grains per 1000 ft3 and should be considered if the dust concentration exceeds 1 grain per 1000 ft3 The use of prefilters is recommended in engineered safety feature (ESF) systems for nuclear reactors.lX The decision to install prefilters should be based on providing the best operational balance between HEPA filter life, with its attendant decrease in HEPA filter change frequency, and procurement and maintenance costs for the prefilters

SERVICE LIFE (months)

(b) HEPA FILTER WITH PREFILTER

Fig 2.4 Comparison of HEPA filter life with and without

prefilter HEPA filter replaced at 4 in.wg pressure drop and

prefilter replaced when pressure drop across it reaches twice the

clean-filter pressure drop From P.A.F White and S E Smith,

eds., High Efficiency Air Filtration, Butterworth & Co., London,

1964

Duct-entrance prefilters can be changed' without

entering or interrupting the central air cleaning

facility, can minimize dust buildup in the ducts, and

can provide a measure of protection against duct

corrosion, accidental high-moisture loadings, and

flaming trash or sparks that may be produced by a

fire in the working space On the other hand, a system

that has a number of local prefilter installations may

cost from two to three times as much as one in which

the same prefilter capacity is installed in a central

housing."

Prefilters in a central air cleaning system sholild

not be attached directly to or installed back-to-back

to HEPA filters; they should be installed on a

cd

23

separate mounting frame located at least 4 to 5 ft upstream of the HEPA filters This installation requires more building space and higher investment costs (particularly when building space is at a premium), but it is justified by increased safety and greater system reliability Adequate space between prefilters and HEPA filters is needed for access and maintenance and to minimize the propagation of fire

by sparks or direct flame impingement If the possibility of fire is a serious consideration, a removable screen, fine enough to stop sparks (10 to

20 mesh), may be installed on the downstream side of the prefilters

2.3.5 Operation to High Pressure Drop Most HEPA filter manufacturers' literature suggests the replacement of HEPA filters when the resistance due to dust loading has reached 2 in.wg However, HEPA filters, by specification, are capable

of withstanding a pressure drop, when clean, of at least I0in.wg without structural damage or reduction

of efficiency" (see Chap 3) Replacement at a

pressure drop of only 2 in.wg, when other factors such as radioactivity and fan capacity do not have to

be considered, is underutilization of the filter At many ERDA facilities, HEPA filters are operated routinely to pressure drops as high as 4 to 5 in.wg

Figure 2.5 shows the effect of such operation on filter life and maintenance costs

The advantages of operating to high pressure drop must be weighed against first cost (higher-static- pressure fans, larger motors, and heavier ductwork), higher power costs, and less efficient fan operation The installed fan and motor must have sufficient capacity to deliver the design airflow at the maximum differential pressure to which the system will operate, with the filters at maximum dirty-filter pressure drop

prior to' change Consideration must therefore be given not only to the increased installed capacity required to operate to the higher pressure drop, but also to the fact that the fan operates at a penalty for much of the time to provide the required airflow over the wide span of pressure drop between installation and replacement of filters

The cost of ductwork, on the other hand, may not

be significantly affected by operation to a high pressure drop because there is a minimum sheet-

operations, 16 gage for field operations) for effective welding, regardless of pressure requirements (see Chap 5) The cost of fans and motors is a function of

24

ORNL OWG 698694R

Ap = PRESSURE DROP ( i n 4 Fig 2.5 Effect of operating HEPA filters to high prrssure

drop on filter life and maintenance cost (including replacement

filters and labor) From W.' V Thompson, High Efficiency

Particulate Filter History and Activities as of August, 1964, I 17-8,

C, DR F H, KE, and K W Buildings, USAEC Report RL-REA-

1000, Hanford Atomic Products Operation, April 12, 1965

the maximum total pressure that must be developed

Fan horsepower can be estimated from the

equation 2"

where

hpf= fan horsepower,

system, in.wg, at time of filter replacement,

E'= fractional efficiency of fan (0.60 usually

assumed for estimating)

Motor horsepower can be estimated from the

E,,, = fractional motor efficiency (0.90 usually

assumed for estimating for 20-hp motors and

larger)

Annual power costs can be estimated from the equation 2"

(2.3) where

C z a n n u a l power cost, dollars,

h = hours of operation per year,

r = cost of power, cents/ kWhr, E'f and Em = efficiency of fan and motor, respec-

tively, over the period of operation from filter installation to replace- ment; these will be less than the design efficiencies

Although investment and power costs will be lower for the system operated to 2 in.wg pressure drop, the total annual cost of owning the system, including materials and labor costs for filter replacement, may

be less for the system in which HEPA filters are replaced at pressure drops on the order of 4 to 5

in.wg Total savings for the facility as a whole may be even greater when the reduced interruption of building operations due to the reduced frequency of filter change is taken into consideration

Some prefilters can be operated to higher pressure drops than recommended by their manufacturers In Great Britain prefilters are commonly operated to dirty-filter pressure drops of 3 to 4 in.wg.21 This results in less frequent prefilter change than if the prefilters are changed at a pressure drop of only two

or three times the clean-filter pressure drop (usually 0.1 to 0.5 in.wg) recommended by most manufac- turers Care must be taken in the selection of prefilters Because of the many types, efficiencies, configurations, and constructions available, the designer must specifically investigate the safe over- pressure allowance for the particular model under consideration Figure 2.6 shows clearly the results of

overpressuring prefilters In this case the problem of filter blowout was overcome by working with the manufacturer to reinforce the filter itself Some benefit could also have been obtained by installing a screen or expanded metal grille on the downstream face of the prefilters against which the filter cores could bear; in any event, screens or grilles would have prevented damage to the HEPA filters when pieces of

prefilter struck them

2.3.6 Underrating The service of all internal components, except

25

Fig 2.6 Resdtaf:merpneewiring pnfdters Note damage to

HEPA filters in ,rear Courtesy Union Carbide Corporation,

Nuclear Division, rY-I2 Plant

pressure drop for a given level of d u s t h a d i n g a m b e

reduced 'rby underrating-that is, by ioversizing bhe

system and installing more filter and adsotber

-capacity than is required, based on nominal airflow

rating of those components, to meet system design

airflow needs Figure 2.7 showstthat the increasetin

filter life obtainable by underrating is roughly pro-

portional to the square root of the degree ofunder-

rating A study by the Harvard Air Cleankg

Laboratory suggests that the economic limit of

underrating is about 20% (Le., system design.airflow

egual to 80% of installed airflow capacity).''

:Overrating The operation of a system at airflows

greater than the installed airflow capacity of the

\system should be avoided, particularly in systems

!with radioiodine adsorbers whose performance 'is

dependent on residence time of air within the

adsorbent bed When airflow rates exceed rated

airflow capacity of HEPAdilters, filter 1ife.decreases

more rapidly than the eguixalent increase ;in rflow

rate, as can be seen from the IIBO%.curve:in'Fig 2.7

As noted above, the residence3ime of contaminant-

laden air in adsorber units is inversely related to

airflow rate; overrating of these units decreases their

ability to trap gaseous contaminants and thereby

degrades their function

2.3.7 Uniformity of Airflow

In large air cleaning systems, because of the stratification of airflow due to poor transitions between ducts and housings or between housings and fans or because of poorly designed housings, filters

or adsorbers at the center of a bank may receive higher airflow than those on the periphery of the bank This not only results in nonuniform dirt loading of filters but may result in excessive penetra- tion of :tihose HEPA filters closer to the air intake if the degree m'f ;airflow nonuniformity is great Figure

2.8 shows >%hat &he penetration of HEPA filters by very small partioles is directly velocity-dependent and increases signiticantly at very high airflow rates Conversely, the peneiration of HEPA filters by particles larger than rl :pLm may increase at very low flow rates due to theaeduction in effectiveness of the impaction mechanism on which trapping of those particles depends If some filters are operating at very high airflow and some at very low airflow, as could happen h a poorly,designed housing and filter bank,

it is possiMe tthat significant penetration could occur even though (the (filters are in good condition Low

flow rates improve the efficiency of radioiodine adsorbers, but high flow rates decrease efficiency, as discussed in the previous section Therefore, signifi- cant nonuniformity of airflow through a bank of adsorber cells can reduce the overall efficiency for

$trapping radioactive gases of interest Figure 4.28

shows a well-designed duct-to-housing transition

ORNL DIG bV-8695 80%

1 25

OPERATING TIME (hr)

Fig 2.7 Effect ,af underrating on eervia life of extended-

medium filtera, I b n d an percentage of m a n u f ~ m r ' s rated filter airflow capacity F r m P M Engle and C J Bauder,

"Characteristics and Application of High Performance Dry

Filters," ASHRA E Journal, American Society of Heating,

Refrigerating zuaU Air-Conditionmg Engineers, May 1964, pp

72-75

VELOCITY THROUGH FILTER MEDIUM (fd

Fig 2.8 Penetration of HEPA fdtcr medium by submicron

particles as function of flow rate through medium Normal flow

rate, at manufacturer’s rated filter capacity, is approximately 5 fpm

(vertical line) From MSA Ultra-Aire Filters, Bulletin No 1505-20,

Mine Safety Appliances Co

that will produce satisfactory airflow distribution

through the banks of filters and adsorbers

2.3.8 Maintainability, Testability

Maintenance and testing are two operational

factors whose cost can be minimized by good initial

design and layout of ventilation and air cleaning

facilities Inadequate attention to maintenance and

testing requirements at the initial phase of the project

can result in operating costs much higher than they

should be Two elements that largely influence the

costs of these functions are the accessibility of

components requiring periodic test and service and

frequency of filter and adsorber replacement In

systems that involve the handling of radioactively

contaminated filters and adsorbers, the frequency of

changing these components and the time to ac-

complish the change can be especially critical,

because the total integrated radiation dose a

workman can be permitted to receive in each calendar

period is limited When all personnel have received

their maximum permissible dose for’the period, the

supervisor faces the prospect of having no one

available to carry out a needed filter change or a

scheduled test Maintenance and testing of radioac-

tively contaminated systems is much more costly than

the same operations in nonradioactive systems

because of the time required for personnel to change into and out of protective clothing; to decontaminate and clean up the area, tools, and equipment after the operation; to dispose of contaminated filters; and to bathe and be monitored by health physicists There is also the extra attention that must be given to filter or adsorber cell installation (as compared with common air filters, for example) If the system does not meet test requirements after the change, the work must be repeated There is also a need for health physics monitoring before, during, and after the operation The fact that personnel have to work in clumsy protective clothing, including respirator or

full-face gas mask, also adds to the time required Regardless of these inherently high time and money costs, proper maintenance and testing are primary factors in ensuring the reliability of the air cleaning system, and they cannot be done properly unless the physical facilities have been properly designed and built

measures that reduce the frequency of filter (HEPA

and prefilter) and adsorber replacement also reduce system costs and downtime Several of the factors discussed earlier-the use of good building supply-air filters and prefilters, operation of HEPA filters to

high pressure drop, and underrating-serve to extend component life and reduce the frequency and cost of service Exhaust system HEPA filter and adsorber

installations must be tested after each component change so that any extension of service life also directly reduces testing costs

Accessibility When laying out ventilation and air

cleaning facilities the designer must consider the location of fans, dampers, instruments, and filter housings and working space adjacent to them; working space and spacing of banks within man- entry housings; height and array of filter and adsorber banks; and routes to be used for moving new and used filters and adsorbers between storage, installation, and disposal areas Failure to provide adequate space in and around housings and mechanical equipment (fans, dampers, etc.) results in high maintenance and testing costs, inhibits proper care and attention, creates hazards, and increases the chance for the accidental spread of contamination during service or testing operations Recommen- dations for the arrangement and space requirements

and 7 Even greater space requirements are needed

for remotely maintainable systems

Ease of Maintenance Simplicity of maintenance

and testing is a primary factor in minimizing the time

personnel must remain inside a contaminated hous-

ing and restricted areas of a building during a filter or

adsorber change or test and is, therefore, an impor-

tant factor in reducing both personnel exposures and

costs Simplicity of maintenance and testing is

achievable through the following means:

1 A housing layout that minimizes reaching, stoop-

ing, and the use of ladders or temporary scaf-

folding for gaining access to filter or adsorber

cells Some reaching and stooping are un-

avoidable in man-entry housings, but it should

not be necessary for workmen to go through

physical contortions or climb ladders to femove

and replace filters in single-filter installations

Similarly, in bank systems it should not be

temporary scaffolding to gain access to the upper

tiers of filters or adsorbers

2 Adequate finger space ( 1 in minimum is

desirable) between filter elements and provision

of handles on heavy components such as ad-

mounting frame for aligning and supporting

filters (adsorbers) prior to clamping to face-

sealed mounting frames (see Sect 4.3.5)

Simple filter and adsorber clamping devices A

properly designed bolt-and-nut clamping system

has proven most satisfactory in the past,

although numerous methods of minimizing or

eliminating loose parts are currently being in-

vestigated Toggle clamps, over-center latches,

and other devices are easily manipulated and

require no tools; however, they often tend to jam,

become difficult to operate, or lose their ability to

properly clamp the filter or adsorber cell after

extended exposure to the hostile environment of

a contaminated air cleaning system Such devices

should be used only after due consideration of

the difficulties that would be involved in replac-

ing them in a contaminated system (see Sect

4.3.4)

Elimination of ledges and sharp corners that a

or tear his protective clothing on

Adequate lighting in and adjacent to the filter

house and adjacent to other items that require

periodic service, inspection, or testing

or applied during decontamination of the area after a filter or adsorber change Drains must be designed so that no air can bypass filters or adsorbers

Availability of electrical, water, and compressed air connections nearby, but in no case inside, the filter house

Materials-handling facilities, including dollies for moving new and used filters and adsorbers, hoists or other means of handling the heavy adsorber cells in systems containing those com- ponents, and elevators or ramps for moving loaded dollies up and down within the building Location of filter housings inside the building It

is undesirable for personnel to (a) conduct a filter change or test out of doors where wind or rain may cause a spread of contamination, (b) cross a

roof to gain access to a filter house, or (c) wait for good weather to carry out a scheduled filter or

adsorber change or test

Rigid, double-pin-hinged doors on man-entry housings large enough for personnel to pass through without excessive stooping or twisting

It should not be necessary to remove several dozen nuts from a hatch t o gain entry to a man- entry or single-filter housing Not only is this too

time consuming, but nuts tend to cross-thread or gall to the extent that it is often necessary to cut off the bolt to open a hatch; or the nuts get dropped and lost and are often not replaced, thus compromising the seal of the hatch Sliding doors are not suitable because they will jam with any distortion of the housing wall (see Sect 4.5.7) and are difficult to seal

Nearby decontamination and clothing-change facilities (including showers)