NCRP report no 118 radiation protection in the mineral extraction industry

An effective radiation safety program thus includes evaluation of situations which may lead to radiation exposure, comparison of expected exposures to exposure limits mandated by regulat

NATIONAL COUNCIL O N RADIATION

PROTECTION AND MEASUREMENTS

Issued November 30,1993

National Council on Radiation Protection and Measurements

7910 Woodmont Avenue 1 Bethesda, MD 20814-3095

LEGAL NOTICE

This report was prepared by the National Council on Radiation Protection and Mea- surements (NCRP) The Council strives to provide accurate, complete and useful information in its reports However, neither the NCRP, the members of NCRP, other persons contributing to or assisting in the preparation of this Report, nor any person actingon the behalf of any of these parties: (a) makes any warranty or representation, express or implied, with respect to the accuracy, completeness or usefulness of the information contained in this Report, or that the use of any information, method or process disclosed in this Report may not infringe on privately owned rights; or (b) assumes any liability with respect to the use of, or for damages resulting from the use of any information, method or process disclosed in this Report, under the Civil Rights Act of 1964, Section 701 et seq as amended 42 U.S.C Section 2000e et seq (Title VII) or any other statutory or common law theory governing liability

Library of Congress Cataloging-in-Publication Data

National Council on Radiation Protection and Measurements

Radiation protection in the mineral extraction industry : recommendations of the National Council on Radiation Protection and Measurements

Preface

This Report was originally intended as radiation protection recom- mendations for the uranium mining and milling industry The Com- mittee early on, however, recognized t h a t there were known radiation problems connected with the mining and milling of several minerals Further, the Committee recognized that the extraction and processing of virtually any mineral might result in some level

of radiation exposure and that the application of radiation protection practices may be warranted in some cases Therefore, the Report that evolved addresses the whole mineral industry and the material prepared for the uranium mining and milling industry was retained

to provide examples of the more complex problems encountered and solutions to those problems

The Report was written for a specific audience-management and its technical staff-who either have been made aware of radiation problems by the imposition of a regulation or perceive the importance

of evaluating facility design and operations in the societal context

of a greater awareness about occupational and environmental risks The International System of Units (SI) is used herein and, in accordance with the recommendations set forth in NCRP Report

a conversion table of SI units and conventional units

nium Mining and Milling-Radiation Safety Programs, working

tion Safety

Pennsylvania Power and Light Company

Allentown, Pennsylvania

Members

iv 1 PREFACE

Charles E Roessler Edwin T Still

Scientific Committee 46 Liaison Member

Keith Schiager

University of Utah Salt Lake City, Utah

Serving on Scientific Committee 46 were:

Kenneth R Kase, Chairman (1990- )

Stanford Linear Accelerator Center

Stanford, California

Charles B Meinhold, Chairman (1983-1990)

Brookhaven National Laboratory

Upton, New York

Members Ernest A Belvin (1983-1987) David S Myers (1987- )

National Laboratory Livermore, California

W Robert Casey (1983-1989) John W Poston, Sr

College Station, Texas

Robert J Catlin (1983-1992) Keith Schiager (1983- )

Joyce P Davis (1990- ) Ralph H Thomas

Livermore, California

William R Hendee (1983- ) Robert G Wissink

St Paul, Minnesota

PREFACE 1 V

James E McLaughlin (1983- ) Paul L Ziemer (1983-1990)

Washington, D.C

Thomas D Murphy (1983-1992)

U.S Nuclear Regulatory

Commission Washington, D.C

Charles B Meinhold

President, NCRP

Bethesda, Maryland

August 1,1993

Contents

Preface 1 Introduction

1.1 Purpose

1.2 Concepts of Radiation Protection

1.3 Scope of Report

2 Design of Radiation Protection Programs

2.1 Criteria for Radiation Protection Programs

2.2 Program Management

2.3 Radiation Safety Officer

2.4 Radiation Safety Committee

2.5 Preparation and Maintenance of Records

2.6 Quality Assurance Program

2.7 Coordination Among Safety Programs

3 Sources of Potential Radiation Exposures

3.1 Source Characterization

3.1.1 Naturally Occurring Radioactive Materials 3.1.2 Distribution of Radioactivity in Ore Product, By-Products and Wastes

3.1.3 Characteristics Related to Radiation Dose

3.2 Occupational Exposures

3.2.1 External Radiation 3.2.2 Airborne Radioactivity

3.2.3 Surface Contamination

3.3 Releases to the Environment

3.3.1 Airborne

3.3.2 Waterborne

3.3.3 External Radiation

3.4 Process By-Products and Waste Materials

4 Exposure Management Program 4.1 Exposure Limits

4.2 Exposure Environment

4.2.1 External Radiation 4.2.2 Ore Dust

4.2.3 Airborne Radon and Radon Progeny 4.3 Facility Design and Engineering

4.3.1 Site Selection 4.3.2 Facility Layout

4.3.3 Equipment and System Design

vii

viii I CONTENTS

4.4 Facility Procedures and Practices

4.4.1 Access Control

4.4.2 Radioactive Material Control

4.4.2.1 Materials Handling 4.4.2.2 Waste Management

4.4.2.3 Sealed Source Control

4.4.3 Personnel Protective Equipment

4.4.3.1 Respiratory Protection

4.4.3.2 Protective Clothing 4.5 Employee Training

5 Monitoring of Occupational Exposure

5.1 Monitoring Objectives

5.1.1 Characterization of the Workplace

5.1.2 Personnel Exposure Assessment 5.2 Monitoring Program

5.3 External Radiation

5.3.1 Characterization of the Workplace 5.3.2 Personal Monitoring-External

5.4 Long-Lived Airborne Radionuclides

5.4.1 Characterization of the Workplace

5.4.2 Personnel Exposure Assessment-Internal 5.5 Airborne Radon and Progeny

5.5.1 Characterization of the Workpla~e-~~~Rn and

Progeny 5.5.2 Personnel Exposure Asse~sment-~~~Rn and

Progeny 5.5.3 Radon-220 and Progeny

5.5.4 Monitoring for Control Purposes 5.6 Surface Contamination

5.6.1 Area Monitoring

5.6.2 Monitoring of Personnel

5.6.3 Monitoring Other Items

5.7 Bioassay

5.7.1 Bioassay Methods

5.7.2 Bioassay Program Content

5.7.3 Routine Bioassay

5.7.4 Post-Exposure and Follow-Up Measurements 6 Effluent Monitoring and Environmental

Surveillance 6.1 Environmental Pathways

6.2 Effluent Monitoring

6.2.1 Effluent Monitoring Objectives 6.2.2 Program Design

6.2.3 Air Monitoring

6.2.4 Water Monitoring

CONTENTS 1

6.3 Environmental Surveillance

6.3.1 Environmental Monitoring Objectives 6.3.2 Program Design

6.3.3 Radon

6.3.4 Radon Progeny 6.3.5 Long-Lived Airborne Radionuclides

6.3.6 Soil and Vegetation

6.3.7 Water

6.3.8 External Radiation

7 Guidelines Standards and Regulations

7.1 General

7.2 Sources of Guidance and Standards

7.2.1 Scientific Recommendations 7.2.2 Consensus Standards

7.2.3 Federal Guidance and Policy

7.2.4 Rules and Regulations

7.3 Approaches to Radiation Limits

7.4 Occupational Exposures

7.4.1 Introduction

7.4.2 Recommendations

7.4.3 Standards and Regulations

7.5 Effluents and the Environment 7.5.1 Emuents

7.5.2 Wastes 7.5.3 Uranium and Thorium Processing Sites

7.5.4 Other

8 Radiation Emergency Response Planning

8.1 General 8.2 Operations

8.3 Environment

8.4 Transportation 9 Radiation Protection in Specific Applications

9.1 Introduction 9.2 Heap-Leach Extraction

9.3 I n situ Mineral Extraction

9.4 Side-Stream Extractions of Uranium

9.4.1 Uranium Recovery from Phosphoric Acid

9.4.2 Occupational Exposure Considerations 9.4.3 Shipping and Transportation

9.4.4 Efluents and Environmental Monitoring 9.4.5 Solid Radioactive Waste and Equipment Reuse or Salvage

9.5 Thorium and Rare-Earths Processing

X 1 CONTENTS

9.6.1 Mining Beneficiation and Wet Rock

Handling

9.6.1.1 Occupational Exposure 9.6.1.2 Mining and Beneficiation Wastes and

Post-Mining Land

9.6.1.3 Liquid Releases and Water Quality 9.6.2 Phosphate Rock Drying and Dry Rock Handling

9.6.2.1 Occupational Exposure

9.6.2.2 Emissions

9.6.3 Wet-Process Phosphoric Acid Plants

9.6.3.1 Occupational Exposure-Protection Operations

9.6.3.2 Occupational Exposure-Clean-up and Maintenance

9.6.3.3 Occupational Exposure-Filter Pan Repair

9.6.3.4 Waste Management

9.6.3.5 Phosphogypsum

9.6.4 Production of Phosphate Products

9.6.5 Thermal Process (Elemental Phosphorus)

Appendix A Radioactive Serie~.~~'U and ='U

Appendix B Conversion Factors

Glossary

References

The NCRP

NCRP Publications

Index

1 Introduction

1.1 Purpose

The National Council on Radiation Protection and Measurements (NCRP) develops recommendations dealing with various aspects of operational radiation protection The basic principles and practices

of radiation safety are well established However, specific facilities present specific problems To serve the needs of a particular facility, effective programs should recognize and account for variables such

as the complexity of radiation exposure pathways and the magnitude

of potential radiation exposure a t a given facility This Report describes the vital parts of an effective radiation safety program for mineral extraction facilities It provides information useful for choosing appropriate techniques of radiation control and monitoring

a t such facilities

Because radioactive material occurs naturally throughout the earth's crust, any mineral extraction operation or process, not just those commonly perceived to be processing radioactive materials, is

a candidate for radiation safety measures This Report draws on examples from the uranium mining and milling industry, but princi- ples and practices common across the entire mineral extraction industry are emphasized

Mining, milling and beneficiation have long been accepted techno- logies for extracting and processing ores However, they are among the technologies that have come under increasing scrutiny from

a society concerned about occupational and environmental risks Increasing awareness and attention has been placed on the potential uses and risks of radioactive materials Therefore, assessing the radiation protection requirements and practices of the mineral extraction industry is both timely and consistent with good work practices

This Report is written so that individuals with a basic technical

any mineral extraction operation Management can use the Report

to define the degree to which radiation safety should be considered

in designing facilities and planning their operation Design engi- neers as well a s health and safety professionals will find useful

Radiation protection programs are designed to allow society to gain the benefits of using radioactive materials while minimizing risk to the public and workers In the case of mineral extraction, the goal is to make sure that minerals can be extracted and processed while keeping risks from radiation exposure to a minimum The key

is to make sure exposures are evaluated and controlled effectively Most situations involving exposure to radioactive materials can

be managed easily because exposure to personnel can readily be maintained well within established exposure limits; the radiation risk is controlled using simple and inexpensive techniques As expo-

complex and expensive controls need to be considered One goal of the radiation safety program is to make sure that both users and the public are protected a t reasonable cost Adequate protection means that risk should, as far as possible, be limited to levels compar- able with those experienced in other safe industries (NCRP, 1993)

many scientific studies which have been performed and which have resulted in adoption of what is called the "linear no-threshold hypoth- esis." In simple terms, the assumption is that for any increase in exposure, there is a corresponding increase in risk Applying the theory to real-life situations has its complications Biological effects that can be produced by radiation are also caused by other physical and chemical agents and also occur naturally Above-normal inci- dence of these effects (e.g., several types of cancer) has been observed

in individuals exposed a t radiation levels greatly in excess of those discussed in this Report as individual exposure "limits." To assess the more common exposure situations, scientists extrapolate from the number of observed effects a t high exposures to predict the num- ber of presumed effects at lower exposures The difficulty arises primarily because, a t low exposures, there is a very low probability

1.3 SCOPE OF REPORT / 3

that radiation-induced effects will occur Further, any effects that

do occur are indistinguishable from those induced by other agents and those normally seen frequently in any population The assump- tion is made that effects will result from exposure of a population

to radiation and that the number of people affected, or the risk to a specific individual, will be in direct proportion to the total radiation exposure This cautious assumption may overestimate risk but has been adopted by the NCRP for purposes of radiation protection Because any radiation exposure is assumed to have an associated

risk, exposures are to be maintained a t levels which are as low as reasonably achievable (ALARA), economic and social factors being taken into account The inclusion of the word "reasonably" recognizes both that the use of radioactive materials can yield benefits to society and that exposure reduction often requires resource expenditures Achievement of exposure levels which are ALARA reflects the appli- cation of exposure reduction techniques until further reduction can

be attained only if the intended benefit would not be obtained or the cost would be unreasonable Exposure management to levels as low

as reasonably achievable is accomplished by controlling a number

of variables: the quantity of radioactive material, the location of workers and the public relative to the material, the length of time people are exposed to the material, the amount of material that inadvertently escapes from processing streams, and the effluents that contain radionuclides and are released to the environment

An effective radiation safety program thus includes evaluation

of situations which may lead to radiation exposure, comparison of expected exposures to exposure limits mandated by regulation, and the application of control practices to maintain exposure at levels which are ALARA

1.3 Scope of Report

This Report describes the application of radiation safety concepts

to mining, milling and beneficiation facilities The potential for radi- ation exposure differs in magnitude depending on the mineral and the facility type However, the same basic principles of radiation safety should be applied to facility design and operations For some facilities, the application of these principles may mean the establish- ment of a radiation safety program because radiological protection had not previously been considered relevant to the operation There- fore, this Report emphasizes fundamental concepts, simplifies techni- cal terminology and presents methods based on past experiences

4 1 1 INTRODUCTION

with mineral extraction This Report will deal primarily with design and operation The decommissioning of facilities and reclaiming of the facility site are beyond the scope of this Report

Each section of this Report presents a piece of the total picture on how to design and operate an effective radiation protection program

In Section 2, organizational structures applicable to different pro- gram needs are discussed; while in Section 3, the characterization

sure are addressed In Section 4, management of radiation exposures

by facility design and in facility operations is described Concepts

of monitoring occupational radiation exposure are considered in

regulations, standards and guidelines are presented Emergency

concepts applicable to any mineral extraction facility are illustrated, and guidelines are provided for program implementation Uranium extraction is specifically discussed to illustrate program elements

extraction processes and to direct the reader to an appropriate level

of radiological control for those processes In the last section of the Report, Section 9, information is presented about radiation safety practices for some specific extraction processes, such as phosphate mining and processing operations

2 Design of Radiation

protection Programs

Managers of mineral extraction facilities are responsible for ensur- ing that health, life, property and the environment are protected during the conduct of operations This requires a knowledge of the particular types and levels of risk associated with their facilities In some cases, the predominant risk may be from common industrial hazards; in others, from toxic materials When exposure to radiation

given to radiation safety measures necessary to protect the health and safety of employees and the general public

The motivation to develop an effective radiation safety program can come from several sources For some processes, regulations man- date evaluating risks associated with naturally radioactive materi- als in ore and waste products Other extraction processes are unregulated (for purposes of radiation protection) but may result in

Other motivators include corporate policy, the societal trend toward litigation where exposure to a risk-producing agent is involved, and, most important, concern for the health and welfare of both employees and the public

Whatever the motivation, there is a need for making responsible decisions about the level of radiological control appropriate to a given facility In the process of developing a specific radiation safety program, each of these motivators should be considered The goal is that outlined in Section 1.2: Evaluating facility operations with the aim of reducing exposures to levels which are within established limits and ALARA

If this intent is met, several benefits may result, including reduced risk to individuals, improved worker morale, enhanced public and1

or regulatory agency perception of the facility, and reduced vulnera- bility to workmen's compensation claims or radiation-related litigation

For some facilities, exposure may be routinely so small that an ongoing radiation safety program is unnecessary Assessments such

6 1 2 DESIGN OF RADIATION PROTECTION PROGRAMS

a s those described by Dixon (1984) may be useful in identifying those facilities or processes for which the need for ongoing radiation safety practices should be investigated further As exposure to radiation

or radioactive materials becomes more frequent and as radiation levels become more significant, the application of appropriate levels

of radiation protection controls is warranted Based on the statement

in Section 1.2, the radiation safety program should be designed to limit risks to employees and members of the public to levels compara- ble with risks from other common contributors to risk For example, the level of safety provided for employees should ensure an average risk from radiation no greater than that from all sources of risk for workers in "safe" industries (NCRP, 1993)

Radiation safety programs will vary in staffing and structure, depending on the degree of potential radiation exposure which has been identified and the anticipated difficulty of controlling it This

up a radiation safety program appropriate to the needs of a given facility

Staffing demands will vary with the severity of the conditions a t the facility For example, if the projected exposure for any individual

is well below the annual exposure limit for a member of the public, employing radiation specialists may be unnecessary When t h e potential exposure may approach or exceed this annual limit, consid-

evaluate conditions

For those cases where potential exposures to some individuals are anticipated to exceed the limits for members of the public, staffing becomes a choice between a single organization responsible for both industrial and radiological health and safety, or a qualified staff dedicated solely to radiation protection At some facilities the first choice may be sufficient At facilities requiring a more extensive occupational (Section 5) or environmental (Section 6) monitoring program, a dedicated staff may be warranted Finally, where radia- tion exposure pathways are more complex or difficult to control, the

of need should rarely occur in the mineral extraction industry, and when i t does, quantities of radioactive materials and potential

zation's role is to provide technical support and equipment, so that

applied most effectively Optimal collaboration between manage- ment and the radiation organization must begin early When radia- tion safety evaluations and criteria are applied as soon as possible

in facility planning, the facility is more likely to be designed and operated in ways consistent with the objective of limiting exposures

in practical, cost-effective ways When the size of potential radiation exposures requires development of ongoing controls, management's responsibility may extend for some period of time, even to the point

of providing maintenance and monitoring programs after facility operations end

Regardless of a radiation organization's specific structure, in order

to control exposure effectively its program should include several features Overall, this means that the authority and responsibility for radiation protection should be allocated to the highest manage- ment level, then emphasized at all supervisory levels in proportion to the amount of radiation exposure expected The success of a program

safety This level of commitment is expressed when management provides adequate human and financial resources to implement pro- grams successfully, instills in employees an awareness of their own responsibility for safety, and evaluates program effectiveness on an ongoing basis In short, this means that management must apply

effective safety program that it applies to producing ore or any other end product

In addition, program success depends on making workers aware

of the role they play in reducing unnecessary radiation exposures Specifically, they need to accept the importance of complying with radiation safety rules and reporting potential problems, such as malfunctioning equipment and procedural violations Tools a r e available for building this compliance: policy statements, training programs and less formal communications, including the example set by supervisors and managers The training of individual workers

to be keenly aware of their own responsibility for radiation safety

is crucial to ensuring the effectiveness of any radiation protection program

8 1 2 DESIGN OF RADIATION PROTECTION PROGRAMS

2.3 Radiation Safety Officer

Employing a Radiation Safety Officer (RSO) is warranted for those (few) mineral extraction facilities where exposure pathways are com- plex and difficult to control At those facilities, the RSO should supervise the radiation safety program, providing technical advice

as needed To be fully effective, the RSO should report to senior

lations and administrative policies a t all levels of the organization

In addition, the RSO should be provided with adequate resources and not be assigned duties which may lead to a conflict of interest where radiation safety is concerned

This level of authority does not, however, imply total responsibil- ity A radiation safety program is most effective only when everyone

of reducing risk to a level which is ALARA The RSO's responsibilit- ies, therefore, also include guiding the operations groups so that they consider measuring, evaluating and controlling radiological conditions whenever they are performing either their ongoing activi- ties or planned changes To be effective, the RSO may need to develop safety rules that are specific to that facility or organization The RSO should possess a combination of education, radiation protection experience and appropriate training consistent with the magnitude of potential radiation risk and the complexities of the specific program In some facilities, one person may appropriately perform all the RSO and industrial hygiene or safety functions Other facilities, particularly those which must deal with more varied sources of radiation, may require a t least one professional with more specialized education and experience

In some cases, management should establish a radiation safety committee to help define program scope and enhance their ability

to review a program's effectiveness This committee may be set up for any facility but is especially useful in those cases where potential radiation exposures approach the dose limits The RSO may work

posed of several people aware of the facility's radiation protection program and needs For example, the committee might include supervisors of maintenance, production and engineering It should review radiation safety analyses of operations and facility operating

2.5 PREPARATION AND MAINTENANCE OF RECORDS / 9

procedures, assessing the need for increased management attention

to the radiation safety program It may also review specific radiation safety issues, providing advice on how to reduce radiation exposure, and work on improving communications between employees and facility management

2.5 Preparation and Maintenance of Records

Systematic record keeping documents the extent to which the radiation safety program has been implemented and provides a means for determining how effective it has been in meeting its objec- tives Specifically, this documentation demonstrates that potential exposures have been evaluated and appropriate controls instituted Its value becomes apparent when questions are raised about how well workers and the public have been protected from unwarranted exposure and the assumed risks associated with that exposure

To be effective, this record keeping should include certain basic data Records should describe both the radiological conditions found

a t the facility and the radiation doses received by workers In addi- tion, sufficient data should be maintained so that the environmental impacts of the facility can be assessed It should also be possible to define patterns of radiation levels and exposures for the various modes of the facility's operation In setting up this records system, management should consider the potential need for interpreting and comparing data among similar types of facilities and against established radiation protection standards and guidelines

The extent of the record keeping system and the types of records maintained vary with the complexity of the radiation safety pro- gram, the more complex the program (due to factors such as higher potential exposures, multiple pathways of receiving exposure or mul- tiple radiation sources), the larger the records system required The types of records which may be generated and retained include the following:

a radiation surveys,

b surface contamination surveys,

c airborne radionuclide concentrations, usually for radon and1

or its progeny and for airborne particulate matter,

d radioactive materials inventory and disposal;

a effective dose from external radiation and how it was determined,

10 / 2 DESIGN OF RADIATION PROTECTION PROGRAMS

b committed effective dose from intake of radioactive materi- als (eg., by inhalation) and how it was determined; in many cases, the maintenance of individual records of duration

of exposure multiplied by corresponding concentration of airborne radioactive material is appropriate,

c bioassay data needed to estimate any uptake of radioactive materials by personnel;

b environmental modeling and/or monitoring; this may include descriptions of meteorological, climatological and hydrological data used in modeling and assessment efforts,

c estimates of individual and collective doses to the public;

a safety assessments of designs and operations; this may include rationale regarding why extensive radiation control measures were not necessary for the facility,

b descriptions of unusual operational events involving the potential for radiation exposure; this includes descriptions

of corrective actions and/or measures taken to prevent recurrence,

c standard operating procedures and relevant corporate policies,

d training course descriptions and rosters,

e quality assurance data; for example, records on radiation measuring instruments and their calibration

Records should be dated to enable reconstruction of the radiation safety program for any time period Recommendations on the form, content and retention of radiation program records are provided in

The length of time for retaining these records varies with the document Records of exposure of individuals may need to be main- tained for a t least the lifetime of the individuals When facility

records should be evaluated Three criteria applicable to the evalua- tion should be applied:

(1) Will the records be needed for medical or legal reasons to

establish radiation exposure history for individuals?

to establish the radiological conditions of the site? and

regulations?

If these questions cannot be definitively answered, the prudent choice may be to retain records until the uncertainties are resolved

2.6 QUALITY ASSURANCE PROGRAM 1 11 Facility management should consider compiling and publishing the pertinent results of research, modeling and monitoring This assists the scientific community in its ongoing evaluations and com- munications of exposure and risk

A quality assurance program for radiation safety is designed to provide confidence among managers, workers and regulators that the radiation safety program is meeting its objectives The quality assurance scope is broad, encompassing all the activities associated with defining job scope, measuring job performance, and verifying and documenting successful work completion This means that high quality programs demand high levels of commitment to quality in every aspect of a program: facility design, operating plans and proce- dures, adherence to those plans and procedures, and verification and documentation of that adherence

When not only qualitative but also quantitative measurements are required, precision and accuracy become prime objectives Repli- cating and performing controlled tests of survey and measurement techniques enhance the validity and credibility of results Calibra- tions should be performed using sources traceable to the National Institute of Standards and Technology (formerly the National Bureau of Standards) or other recognized standards organizations

In addition, radioanalytical laboratories should participate in a rec- ognized inter-laboratory cross-check program (NCRP, 1991a) Management should also make sure that any ongoing radiation safety program is reviewed and audited periodically Results of these checks allow management to evaluate program effectiveness, define improvements that will better control exposures, and track and docu- ment the ways these improvements are implemented This close surveillance should include the use of frequent inspections During these inspections, the facility's staff can observe operating practices and review the need for corrective actions Also, more formal reviews should be conducted periodically, critically assessing pertinent data from surveys and inspections, personnel exposure and training To get a clearer picture of the program's effectiveness relative to other programs, data should be drawn not only from the facility itself, but also from similar facilities During these reviews, special attention should be given to identifying temporal trends in results and equip- ment or procedural problems These insights can then be used to guide the development of appropriate program changes

12 / 2 DESIGN OF RADIATION PROTECTION PROGRAMS

In addition to conducting a variety of reviews, management should consider including reviewers with differing training and experience Program effectiveness and record keeping should be assessed not only by those directly responsible for the program but by outside observers as well The frequency will depend on the complexity of the radiation safety program Once the reviews are conducted, results should be communicated to management at levels high enough in the organization to make sure that appropriate follow-through will take place, especially changes in operating practices, staffing levels, training and commitment to radiation safety or resolution of other program deficiencies which have been identified

2.7 Coordination Among Safety Programs

the facility's overall safety program After all, the programs share the same purpose: To control risk so people will not suffer adverse health effects or lose the ability to do their jobs To accomplish that purpose, radiation safety professionals use methods similar to those

of other health and safety professionals This means that, when appropriate to the types and levels of risk, the same people may perform both radiation and other safety activities In any case, the radiation safety program should complement the other health and safety programs

Content for a specific program can be developed using four basic approaches:

(1) consolidating data on risk;

risks to other risks;

(3) defining a n orderly process for assessing risk-benefit relation- ships; and

1980a)

In some cases, defining an appropriate control program should include efforts to evaluate separate components of risk simultane- ously For example, in evaluating the control needed for airborne uranium ore dust, exposure to uranium and silica must both be considered Similarly, in evaluating the risk associated with splash- ing of some solutions, both the pH and the concentrations of radionu- clides and their decay products must be addressed Cases may arise which call for protective measures for radiological purposes that

2.7 COORDINATION AMONG SAFETY PROGRAMS 1 13

mitigate nonradiological risks In those rare cases, maximal protec- tion against overall risk should be provided Radiation and other health and safety professionals should work together, assessing the combined risks along with costs of control, then determining appro- priate action (IAEA, 1987) Cooperation is imperative in two areas

of risk control: demonstrating management commitment to safety and instilling in employees an awareness of their own responsibility for safety

Just as development of a total radiation safety program depends

on assessing the impact of specific conditions, medical surveillance, based on the general principles of occupational medicine, should take into account specific working conditions and the potential radia-

3 Sources of Potential

Radiation Exposures

The design and implementation of radiation protection controls

in mineral extraction are influenced by a variety of factors, including ore1 type, ore distribution and quality, mining method, extraction process, land use characteristics, geology and hydrology, and the radiation situation The discussion of the natural radiation environ- ment in this Section brings forth an awareness of the potential for radiation exposure for any extraction operation or process The following discussions of potential pathways to individual exposure (Sections 3.2, 3.3 and 3.4) help relate the existence of naturally radioactive materials in the workplace to those locations and opera- tions for which radiation control practices may be appropriate

3.1.1 Naturally Occurring Radioactive Materials

Naturally occurring radioactive materials of concern in the min- eral extraction industry are predominantly associated with the 238U

active decay series are described in Appendix A

A thorough description of natural radioactivity is found in NCRP Report No 94 (NCRP, 1988a) From the contents of that report, it can be seen that the abundance of uranium and thorium varies widely over geographic areas Igneous and sedimentary rocks on average contain concentrations on the order of 0.5 to 5 mg per kg (conventionally) of 238U and 2 to 20 mg per kg of 232Th These corre- spond to radionuclide concentrations of about 6 to 60 Bq per kg of

'The word "ore" in this Report may refer to either a natural combination of minerals from which an extraction is to occur or a technologically altered combination of minerals from which additional extraction is to occur An example of the latter type

of operation may be the extraction of tin from a slag residue resulting from a previous processing operation

3.1 SOURCECHARACTERIZATION / 15

physical separation processes, an equilibrium is reached in which the number of atoms of each nuclide of a radioactive series that decays during a specific time interval nearly equals the number of decays of the parent nuclide in the series The activity of each mem- ber of the uranium series, for example, would therefore be about 6

to 60 Bq per kg in rock

Chemical and physical separation are common, however, primar-

some nuclides from certain rocks and soils and the relative concentra- tion of others While such concentration and depletion processes create the potential for economical extraction of some minerals, they also result in widely varying radionuclide concentrations over ore types and locations

In the mining and milling industry, personnel extract a mineral which is relatively concentrated In the process, they may contact and receive radiation exposures from nuclides of the naturally occurring radioactive series The magnitude of exposure depends on the charac- teristics of the specific mineral strata and the extraction processes Examples of naturally occurring radioactive materials in mineral resources are listed in Table 3.1 (Gesell and Prichard, 1975; Gesell

et al., 1977; CRCPD, 1981; NCRP, 1988b; Drummond et al., 1990;

IAEA, 1990; EPA, 1991; Johnston, 1991; Pinnock, 1991) The list should not be considered all-inclusive For example, exposures have been attributed also to smelters processing lead and zinc (NCRP, 1987a) and may occur in the extraction of virtually any mineral

In mines, sources of radiation exposures may include external gamma radiation and airborne radon, radon-decay products (prog- eny) and ore dust containing radionuclides Radon and its short- lived progeny often constitute the most important potential exposure source, but the long-lived alpha-emitting materials in ore dust are also of concern The ingestion of radioactive materials and exposure

to external gamma radiation warrant consideration but generally are of less significance (IAEA, 1976a; ICRP, 1977; 1981)

Sources of exposure during the extractive processes are similar

to those in the mine environment However, milling can result in elevated concentrations of various radionuclides at different stages

of the process Consequently, the potential for exposure to airborne radionuclides and to external gamma radiation can be increased relative to that experienced in the mines (IAEA, 1976a)

The uranium and thorium series are also associated with petro-

in natural gas, and 'lOPb and 210Po may be present in condensed

16 / 3 SOURCES OF POTENTIAL RADIATION EXPOSURES

TABLE 3.1-Natumlly occumng mdioaetivity related to mineml resources

Mineral Mineral or waste radioactivity

0.03-100 + Bq U/g ore 0.02-0.11 Bq W g ore Uranium series

4 Bq Ralg (tailings) Uranium series Thorium series Uranium series (tailings) 6-20 Bq U/g sands Thorium series (4% by weight) 2-17,000 Bq Rn/m3 (gas, average for groups of U.S and Canadian wells)

0.4-54,000 Bq Rdm3 (gas, individual U.S and Canadian wells)

0.1-50 Bq 21?Pb,2'0Po/g (scale, residue in pumps, vessels, and residual gas pipelines)

Uranium series Thorium series

Bq RaIL, ranging from mBq to 100 BqIL (brines or produced water)

Bq Ralg, ranging up to 70 Bqlg (sludges)

Bq to tens of Bq Ralg, ranging up to 4,000 Bqlg (scales)

100-4,000 mBq U naturallg ore

15-150 mBq Th naturallg ore 0.6-3 Bq Ra/g ore

Thorium series Potassium-40 Uranium series Thorium series 1-2 Bq Ra/g (ore and slag) 30-750 mBq Ulg ore 35-750 mBq Thlg ore

15 Bq Ra/g (ore)

100 Bq Ralg (slimes) 10-20 Bq Ralg (tailings) Uranium series

Uranium series Thorium series

4 Bq U/g sands 0.6 Bq Thlg sands 4-7 Bq Ralg sands

3.1 SOURCE CHARACTERIZATION 1 17

liquids in residues in pumps, vessels and residual gas piping associ- ated with natural gas processing plants In addition, various mem- bers of the series, principally "=Ra and 228Ra, accompany produced fluids (production water) and entrained sand to the surface where they may be present in the production water, in scales formed in piping and equipment and in sediments found in tanks, equipment and ponds

Under some circumstances there may be the potential for exposure

of operating personnel to external gamma radiation andlor airborne radon, and of maintenance and support industry service personnel to

and airborne contamination The radioactive materials also present challenges for the appropriate disposal of fluids, scales and sedi- ments Still another consideration is the potential for exposure to segments of the general population through salvage and reuse of contaminated piping and equipment

The term "elevated is used in this Report to describe naturally occurring radioactivity that is several times greater than average background The term "enhanced" means the increase over back- ground that occurs when an area is disturbed by human activities

No new radioactivity is produced, but the radionuclides are redistrib- uted in a way that increases the actual or potential human exposure

At present, exposures due to naturally occurring radioactivity are not subject to uniform regulation, but the recommendations of this Report apply to all such exposures in the mineral extraction industry (NCRP, 1984a)

Radionuclides released to the environment through air and water can result in radiation exposures to the public In some cases, final products, process by-products and wastes containing radionuclides have been released for unrestricted uses resulting in unnecessary radiation exposures (NRC, 1980)

3.1.2 Distribution of Radioactivity in Ore, Product, By-Products and Wastes

Managers of mineral extraction industries should determine the distribution of radioactive material at the various stages in the mining, milling and beneficiation processes The extractive process can often significantly alter the distribution of radioactivity from that in the original ore, thus having a significant effect on the poten- tial for, and type of, radiation exposure at different locations within

a plant Identification of the concentrations of radioactive materials

in processes, in the final products or process by-products and in

18 / 3 SOURCES OF POTENTIAL RADIATION EXPOSURES

waste streams is important for radiation protection and responsible decision making

In addition to bringing the radioactive material physically closer

to humans, ore processing may change the chemical availability of the radionuclides with respect to water solubility, plant uptake and metabolic behavior The nature of most chemical processes is such that solubility and similar factors are increased (NCRP, 1984b); however, solubility changes, for example, vary with the extraction process and the radionuclide

Examples of materials containing radioactivity that are generated

by extractive processes are animal feed supplements, fertilizers, den- tal polishing material, soil conditioners, construction fill, wallboard and foundation base, and mine and mill wastes including some slimes The concentrations of radioactive material in these materials vary widely, such as 0.4 to 2 Bq 226Ra per g of solids, 0.03 to 40 Bq '"Ra per L of liquid, and 2,000 to 4,000 Bq 238U per L of liquid (Gesell and Prichard, 1975; CRCPD, 1981; Dixon and Hipkin, 1983) Recently compiled data on construction materials and mining and agricultural products appear in NCRP Report No 95 (NCRP, 1988b) and indicate values from a few to a few thousand mBq 238U per g of material Similar levels of 230Th, 232Th, 226Ra and 'loPo are reported Typical soil in the United States, for comparison, contains about

40 mBq each of '"Ra, 238U and 232Th per g, and the U.S Environmen- tal Protection Agency's (EPA) surface soil standard for remedial actions a t inactive uranium processing sites is 185 mBq n6Ra per g (EPA, 1983a; NCRP, 1988a; 19884

3.1.3 Characteristics Related to Radiation Dose

The potential radiation dose that workers or the public may receive from exposure to radioactive materials is determined by a number

of factors These include the amount of the material involved, the types of radiation emitted by the material, the chemical and physical form of the material, the solubility of the material, the particle size distribution of the material, the duration of the exposure, the amount

of material that may be resuspended from past releases, the disper- sion and dilution conditions a t the time of exposure, the ingestion pathways involving contaminated water, food stuffs and animal feeds, and the demographic and physiological characteristics of the population exposed (ICRP, 1979-1988; 1982; 1991; NCRP, 198413)

3.2 Occupational Exposures

3.2.1 External Radiation

External sources of radiation exposure to mine workers are caused

by the concentrations of naturally occurring radioactive materials

3.2 OCCUPATIONAL EXPOSURES 1 19 present in the deposited mineral, especially the concentrations of the lead and bismuth nuclides that are intermediate in the radioactive series External radiation levels i n most mines a r e less t h a n 0.01 mGy per h and may not be of concern in specific facilities Levels can exceed 0.2 mGy per h and approach 1 mGy per h in uranium mines in areas of selective deposition or exceptionally rich ore bodies

(IAEA, 1976a; ICRP, 1977)

High-concentration uranium- or thorium-bearing ores will have gamma and beta radiation fields present during crushing, grinding and stockpiling operations prior to any physical or chemical process- ing During the processing of ores, chemical reactions can result in changes in the relative concentrations of the naturally occurring radioactivedecay products that are present The concentration of specific radionuclides can be increased; this enhanced concentration depends on the nature of the process, the chemical and physical characteristics of the materials, and the associated carrier materials (Gesell and Prichard, 1975; IAEA, 1978) Piping and process vessels, product bins and waste repositories may have concentrations of natu- ral radioactivity sufficiently high to require protection of workers from external radiation exposures

In addition to the naturally occurring radioactivity in the ores, other potential occupational exposure sources can include gauges and other measuring devices that contain radioactive materials or sources of ionizing radiation These devices are commonly used in flow streams and other areas as part of the process control

3.2.2 Airborne Radioactivity

Airborne radioactivity may occur in both mining and milling pro- cedures The primary airborne radionuclides in uranium and many

other mines are '"Rn and its short-lived progeny, 'laPo (RaA), '14Pb

(RaB), '14Bi (RaC) and '14Po (RaC') In some situations 220Rn (thoron) and its short-lived progeny can be present due to the presence of natural thorium in the ore The concentrations of radon gas and its progeny can vary widely within the same mineral industry as well

as within a single facility The relative concentration of different radionuclides may also vary with a specific process (ICRP, 1977; 1981; NCRP, 1984a; 1984~)

During the milling and extraction processes there may be many situations that provide exposure to airborne radioactivity These include grinding and crushing operations, ore storage, dry feed trans- fer, sampling and analytical procedures, plant maintenance, product

20 1 3 SOURCES OF POTENTIAL RADIATION EXPOSURES

drying and packaging, by-product preparation, waste disposal, trans-

are alpha emitters which can irradiate internal organs of the body after inhalation or ingestion of the particles Other radioactive decay products, such as 'lOPb, can also irradiate internal organs of the body as a result of beta and gamma emissions, and as precursors of other radioactive decay products

3.2.3 Surface Contamination

Transferable surface contamination can be a source of inhalation and ingestion of radioactive materials Therefore, control of surface contamination is an essential component of any radiological protec- tion program Operations that may result in contaminated surfaces include crushing and grinding, process equipment maintenance, agi- tation of solutions, decontamination for the release of equipment for unrestricted use and decontamination in emergency response operations Of particular importance for contamination surveys are areas such as lunch rooms, storage of products andlor by-products and shipment facilities in which both inhalation and ingestion of radioactive material could occur

The following paragraphs describe the release points and release

sections of this Report present additional information on effluents and the environment A figure describing principal radiological expo-

contained in Section 6 (Figure 6.1) and is useful in perceiving the

exposures of members of the public

3.3.1 Airborne

through a number of mechanisms during mining, extraction pro- cesses, final product and by-product preparation, waste disposal, effluent discharge and transportation

3.3 RELEASES TO THE ENVIRONMENT 1 21 Mine ventilation discharges may contain radioactive material, particularly 222Rn and its short-lived radioactive decay products Particulate concentrations, including the long-lived radionuclides of the radioactive uranium and thorium decay series, also are present Dusts having elevated radioactive material concentrations may be resuspended from mine haulage roads Mill exhaust stacks may release significant amounts and concentrations of the radioactive material identified in Section 3.2.2, depending on the operations These operations may include crushing and grinding; sampling and analysis; transfer and conveyance; leach, extraction or separation functions; product and by-product preparation, drying and packag- ing; and waste disposal or retention High-temperature processes such as calcining or sintering may result in releases of radioactive materials to the atmosphere Ore stockpiles can also be a source of airborne emissions (NRC, 1980; NCRP, 198413; 1984~)

Incidents involving spills or other releases during transportation

of raw materials, finished products or by-products can introduce radioactive materials to the environment and expose the general public

3.3.2 Waterborne

The releases of radioactive effluents in sufficient amounts and concentrations to water bodies, waterways and subsurface aquifers can result in elevated radiation exposures to impacted populations These waterborne radioactive releases can occur through planned discharges to the environment, from improperly designed or man- aged impoundments, or during accidents Reactions can occur between process waste liquids and an impoundment's natural or membrane liners, resulting in degradation of the ability of the liner

to contain the liquid Liner degradation can also occur from interac- tions between leachate and underlying soils Such degradation depends on the nature of the radioactive materials involved and the potential chemical and physical interactions of the waste liquid Proper management of impoundment discharge pipes, beaches and freeboard are also important factors in preventing unintentional releases (IAEA, 1981)

Examples of sources of potential waterborne discharges are mine dewatering, aqueous effluents from ore crushing and sorting efforts, mill waste water processing, raffinate and tailing transport and disposal, process vessel and piping rupture, and retention system failures (IAEA, 197613; NRC, 1980; EPA, 198313)

22 / 3 SOURCES OF POTENTIAL RADIATION EXPOSURES

3.3.3 External Radiation

Releases to the environment can increase external radiation lev- els These levels could be from ground surface contamination as a result of prolonged airborne releases or impoundment failures that produce discharges of radioactive materials to surface and ground waters External radiation exposure may also result fiom "shine" (radiation scatter) that can occur from large sources such as a tailings pile or ore stock piles, and from transportation incidents

Uranium and thorium ore mining and milling generate wastes which have most (-85 percent) of the original radioactivity of the ore Other industries (such as phosphate, copper, fluorspar, vanadium, bauxite, titanium and rare earths operations) process ores which often contain elevated concentrations of uranium, thorium and their radioactive decay products Examples of such materials are provided

in Section 3.1.2 Radiation exposures may result from the release, for unrestricted use, of a radioactive process by-product, radioactive waste materials, or contaminated equipment, materials and land Due to the possible wide use of such materials, the resultant collec- tive radiation dose for a segment of a population may become signifi- cant Examples of unrestricted use situations in the past are the use of uranium mill tailings in construction, the use of elemental phosphorus plant slag in roads and building material, building con- struction over phosphate mined lands, fabrication of wallboard from gypsum containing elevated levels of radioactivity, and the manufac-

illustrate a wide range of practices involving potential radiation exposure The scope of this Report does not include evaluations of the various possibilities for material recycling Should facility man- agement choose to explore the reuse of materials, careful evaluations must be made to determine the radiation exposure potential from the release of any product, process by-product or waste materials Once the exposure potential has been defined, decisions can be made for restrictions or controls on use to ensure that exposures are ALARA Coordination with the appropriate regulatory authority is advisable due to the changing nature of regulatory practice (Gesell and Prichard, 1975; CRCPD, 1981; NCRP, 1988b)

4 Exposure Management

Program

The objectives of the radiation exposure management program are

to ensure that individual workers and members of the public do not receive radiation exposures resulting in doses that exceed recom- mended limits and to maintain all radiation exposures a t levels as

these objectives are discussed in this Section and include the basic program elements of design and engineering features, operational practices and training

The principles and methods discussed below include elements which are optimally a part of the management decision making often thought to be applied for purposes other than radiation protection

To improve the cost-effectiveness of operations, facility management

ment types and numbers of worker hours required to produce the end product safely and reliably Proper facility and work planning contribute to radiation exposure management when they lead to the lowest reasonable number of worker hours near radiation sources

4.1 Exposure Limits

The NCRP recommends that annual radiation exposures of work-

approach that value unless the implementation of further exposure control measures is clearly not reasonable NCRP's guidance for cumulative exposure of workers is that the effective dose should not exceed 10 mSv times the individual's age in years For members of the public, the recommended annual limit is 1 mSv where exposure

is continuous or frequent and 5 mSv where exposure is infrequent (NCRP, 1993) I t is important to recognize that the above limits are based on the sum of internal and external exposures

These limits are of a boundary nature and, for routine operations, are the upper limits that should be approached only when the cost

of further exposure reduction is unreasonable This means that even though exposure conditions for most segments of the minerals

24 1 4 EXPOSURE MANAGEMENT PROGRAM

extraction industry are unlikely to cause any individual's exposure

the public, in accordance with the principle of ALARA, is appropriate throughout the industry Simply stated, it is incumbent upon man- agement to assure that all exposures are ALARA, economic and social factors being taken into account (NCRP, 1993) Additional information on guidelines, standards and potentially applicable fed- eral and state regulations is presented in Section 7

4.2 Exposure Environment

external gamma radiation and, to a lesser extent, beta radiation and to airborne radon, radondecay products (progeny) and larger particles ( e g , ore dust) The exposure potential varies significantly

across the different minerals extraction operations and depends upon factors such as geological formations; type, distribution and quantity

of ore; and mining and processing methods Exposure potential typi- cally is greater in underground uranium mining activities than in any of the other minerals extraction operations Typical radiation environments for underground uranium mines and associated mill- ing are described below, because they exemplify the more complex radiation control requirements

External exposure results from radiation emitted during the decay

of uranium and uranium progeny The exposure rate varies with location in the mine and the milling operations, being higher in the ore bodies than in barren rock and relatively high in process areas where radium is concentrated In mines, the gamma exposure rate varies from less than 1 F G ~ per h in shafts and tunnels to 5 to

15 pGy per h near ore faces for ores of 0.2 percent uranium oxide.2 Very high grade ores, on the order of 20 to 30 percent uranium oxide,

(ICRP, 1977; 1986) Beta exposure fields are of less importance

qn this Report, radiation intensity (exposure or exposure rate) is presented in terms of air kerma (see Glossary), expressed in units of Gy or Gy per h (rad or rad per h or R or R per h in the conventional system of units, see Appendix B) At this time, instrument value may be expressed in any of these units 1 Gy = 100 rad ; -

100 R

4.2 EXPOSURE ENVIRONMENT 1 25

although beta radiation dose in air near the ore surfaces may be higher than the gamma dose by a factor of ten (FRC, 1967) The wide distribution of radiation sources in mines and high gamma energies associated with the decay series generally result in uniform

combination with the lower limit on whole-body exposure versus exposure of the skin (or extremities or lens of the eye) generally means that gamma irradiation is more important than beta irradia-

In uranium mills, higher radiation levels (on the order of tens of kGy per h for typical ores) may occur in the vicinity of yellowcake drying and packaging areas, above some of the ore storage piles, and in the vicinity of tailings Sources of gamma radiation may also

in certain piping and process vessels Consideration should be given

in plant equipment in uranium mills and other plants involving chemical processing of minerals

The relative concentrations of the naturally occurring decay prod- ucts change during ore processing Concentrations of specific nuclides may be relatively depleted or enhanced a t specific points

in the process stream However, ingrowth of the beta and gamma emitters will occur in a relatively short period of time in storage areas for finished products such as yellowcake (IAEA, 1976a)

4.2.2 Ore Dust

Ore dust containing uranium and uraniumdecay products may

be suspended in the mine air due to blasting, ventilation and other mining operations Suspension of ore dust also may occur during ore transport, in scale houses and during ore crushing The concentra- tions of the radionuclides are quite variable with time, location and the activities underway In ordinary mining activities, the average concentration of the radionuclides is below 0.3 Bq per cubic m of air (ICRP, 1977) and therefore, on average, below the limiting airborne concentrations specified in regulations (Section 7)

4.2.3 Airborne Radon and Radon Progeny

The most significant source of radiation exposure in the uranium mine environment is radon, a noble gas that is produced by the decay

26 1 4 EXPOSURE MANAGEMENT PROGRAM

concentration of radon can range to high levels-on the order of tens

from the ore, the mining activity and the ventilation The decay of radon can result in the buildup of high concentrations of radon progeny, on the order of tens to hundreds of working levels (WLs) (see Glossary) depending again upon ventilation and mining activi- ties The inhalation of radon progeny represents the principal radia- tion hazard and results in internal exposure to bronchial tissues (NCRP, 1984~)

In mills and other extraction facilities, radon and its short-lived progeny may also build up to concentrations requiring the applica- tion of exposure control methods Higher concentrations are found

in ore storage bins and other areas with lower air turnover rates

4.3 Facility Design and Engineering

Other than the magnitude of the levels, the characteristics of the radiation environment described above for underground uranium mines are similar in other minerals extraction operations Manage- ment has the responsibility for determining the need for exposure management practices in any particular operation and for develop- ing and implementing programs to provide adequate radiation safety The most effective approach in meeting exposure control objectives is through proper design and engineering of facilities Such facilities allow for a much higher degree of safety than can be obtained by dependence upon administrative rules and procedures

result of radiation exposure or safety requirements can be mini- mized Consequently, design and engineering features should receive careful consideration in the planning of new operations and modifi- cation of existing facilities Input a t the early planning stages by individuals knowledgeable about radiation protection requirements will ensure that proper radiation safety features are incorporated

in areas such as site selection, facility layout and equipment, and system design

4.3.1 'Site Selection

The specific location of facilities should take into account factors such as the geologic, meteorologic and hydrologic characteristics of the area as well as the type and quantity of radioactive materials

4.3 FACILITY DESIGN AND ENGINEERING / 27

that may be involved and the potential for exposure to and release

of those materials

The mining operation obviously has to be located at the ore body Surface facilities should be located to keep the potential for unneces-

the environment as low as reasonably achievable This should be done by locating the ore storage pads away from normal traffic areas

to prevent casual and unnecessary contact by workers, and locating the pads in areas protected from surface winds and runoff waters to

tion shafts should be installed vertically to obtain maximum disper- sion and dilution of exhaust air and should be located downwind of the surface facilities and away from populated areas

Ore processing facilities ideally should be located close to the source of the ore This arrangement reduces the distance over which the ore has to be hauled, thereby reducing the potential for loss of control (e.g., spills) and release to the environment In addition, mine drainage water, when available, can be used in the mill process and consolidated with the mill liquid effluent Consideration should also

be given to the proximity of the off-site population, prevailing wind patterns and site geologic and hydrologic characteristics

4.3.2 Facility Layout

The proper layout of facilities is a critical factor in reducing the likelihood and magnitude of exposure to radiation If the material being processed has the potential for causing exposures approaching the nonoccupational exposure limits, the facility should be designed

tain separation of contaminated and noncontaminated areas and to control the movement of personnel into and out of those areas These

is incorporated into the facility design process

The layout of an underground mine is dictated by the ore pattern and the mining method employed Nevertheless, the design should provide for establishing clean areas for lunchrooms and maintenance shops, isolating inactive or mined out areas, and ensuring adequate ventilation in all working areas and passageways The layout of a surface mine should take advantage of site meteorologic and topo- graphic features so that mining activities are predominantly down- wind of the support facilities and precipitation runoff is channeled around or away from the mining activities and any populated areas not directly associated with the mining activity

28 / 4 EXPOSURE MANAGEMENT PROGRAM

The layout of processing facilities normally provides greater oppor- tunity for incorporating exposure reduction features than does the design of the mine Design features that should be considered include the isolation of process vessels and activities where radionuclides would be expected to concentrate, such as the uranium drying and packaging circuit in a uranium mill The layout should provide adequate separation of process areas from nonprocess areas and should group dust-producing activities, such as ore crushing, in the predominant downwind direction from other activities

4.3.3 Equipment and System Design

Specific equipment and system design features can significantly reduce the likelihood and magnitude of exposure of individuals to airborne and external sources of radiation, and the release of radioac- tive materials to the environment from operations and wastes The specific combination of equipment and systems features for exposure- reduction purposes will vary greatly across the minerals extraction industry and will generally be more comprehensive for uranium mining and milling operations

As noted in Section 4.2.3, the principal airborne exposure concern for most underground mining operations is radon and radon progeny Mechanical ventilation is the most effective manner for controlling exposure to these radionuclides Radon enters mine air along ventila- tion passageways and remains entrained until the ventilation sys- tem discharges the air above ground The concentration of radon and its short-lived progeny thereby increases continuously with time

as air travels through the mine Optimizing the residence time of air within the mine is a key factor, necessitating that provision of adequate ventilation equipment and systems be taken into account from the initial design and development stages Ventilation systems should consist of a primary system with high-capacity fans for mov- ing air through main tunnels connected with vent holes and a second- ary system that delivers air from the primary airways to active working areas The secondary system should be modified as required, using small auxiliary fans and flexible ducts, to ensure proper air distribution where individuals are present Overall ventilation sys- tem efficiency may be enhanced by sealing off inactive and aban- doned mine areas and by using doors and bulkheads to channel air through designated areas The use of air cleaning systems to recondition air for further use underground may be evaluated as

inactive mine areas cannot be effectively isolated from active areas,

4.3 FACILITY DESIGN AND ENGINEERING 1 29 additional ventilation systems or altered configurations may be eval- uated to ensure adequacy of exposure control in the active areas

To minimize the in-growth of radon-decay products, the mine ven- tilation system should be designed and operated to ensure the efficient use of air Recommendations for mine ventilation systems can be found in International Commission on Radiological Protection Publication 47 (ICRP, 1986), International Atomic Energy Agency Safety Series No 82 (IAEA, 1987) and various mine engineering manuals

Exposure to ore dust may conceivably be the principal airborne exposure concern This is more likely to occur for surface mines than for the underground mine Should such a situation arise, the use of enclosures and local ventilation equipment should be evaluated as

a means to reduce the airborne radionuclide concentrations near the miners Also, the use of equipment using water or other sprays for dust suppression should be evaluated In underground mines with high-grade ores, ventilation flow rates may require optimization, to reduce dose from inhalation of radon-decay products while maintain- ing acceptable concentrations of resuspended ore dust (Brown, 1992) The equipment and system design measures for protecting against airborne radiation sources in mills differ in degree and type from those in mine operations Airborne radon progeny may build up in locations such as ore storage bins, grinding and crushing areas and

at various processing vessels To reduce the potential for unnecessary exposures, local ventilation equipment should be used to exhaust the air away from working areas and to the effluent treatment system and facility vents To the extent possible, dry process material should

be confined to preclude generation of airborne particulates and if practical, crushing and grinding equipment and conveyor transfer points should be enclosed Similarly, the final product line and pack- aging equipment may need to be enclosed and, in the case of yellow- cake (uranium) drumming, t h e area should be enclosed and maintained under negative pressure

Since most uranium ores do not present an external radiation exposure hazard, specific equipment and system design measures to protect against external exposure are generally not warranted nor are they feasible for underground mining activities Only for ore bodies with uranium content above about one percent are special tools or mining methods likely to be reasonable for control of external exposures in mines However, at various steps in the milling process, radionuclides may be concentrated or accumulated such that increased external exposure potential may be present Where such

a potential exists, the equipment should be designed for accessibility,

30 1 4 EXPOSURE MANAGEMENT PROGRAM

ease of maintenance and ease of installation and removal, and should incorporate other features to reduce the time the worker is required

to spend in the vicinity of the equipment The component should also be constructed, when feasible, of materials that minimize the buildup or collection of process radionuclides

The solid and liquid wastes produced in the minerals extraction

tamination of the environment Equipment and system design fea- tures should be tailored to ensure that these exposure sources are controlled and waste materials are disposed of properly

Groundwater in underground uranium mines is a major source of radon (IAEA, 1987) and may contain other radionuclides that can

be a source of environmental contamination upon discharge to the surface Ventilation measures should adequately control the radon released from mine waters, however, the release underground can

be minimized by use of pipes for conveying the water to pumps and pumping stations and enclosing the pumping stations The radionu- clides contained in the mine water can be removed, or their concen- trations reduced, through treatment systems such as ion exchange media and chemical precipitation The balance to be evaluated is

of personnel operating and maintaining the equipment in which the radionuclide inventory accumulates If evaluations indicate treat- ment systems a r e practicable (consistent with t h e concept of ALARA), equipment and systems should be installed to treat the water Also care should be taken to ensure that drilling and produc- tion-facility shafts are properly designed to minimize the potential for interaquifer exchanges of waters containing radioactive materials

Milling operations produce large quantities of both solid and liquid wastes The solid wastes are tailings, which contain most of the radionuclides that were present in the ore, and worn out, replaced

or obsolete equipment, debris, residues and other materials with radionuclide contamination The tailings should be handled and dis- tributed with remote equipment, where possible, to minimize han- dling by individuals Spraying equipment may be required t o minimize the drying out of tailings and the resultant dust accumula- tion and to control dispersion of radionuclides In some cases, cover- ing the wastes to control the spread of contamination may be

determining the extent and type of contamination on and in the other solid waste materials Depending upon the degree of contamination,

areas limited

4.4 FACILITY PROCEDURES AND PRACTICES 1 31

Mill equipment containing liquids should be covered to prevent generation of airborne aerosols due to splashing Liquids should be discharged through pipes rather than through open conveyances Equipment and systems such as ion exchange media, chemical pre- cipitation, and settling and evaporation ponds should be used to treat liquid waste streams containing concentrations of radionuclides that exceed unrestricted release limits Use of such equipment and sys- tems also would be appropriate should cost-benefit evaluations indi- cate that the control measures are reasonable

Operational procedures and working practices in both mining and milling activities should minimize potential worker exposures and releases of materials to the environment Well-defined and written

employees, are an important component of an effective exposure management program

Operational procedures and practices that should be considered

in reducing potential exposure include access control, general house- keeping, proper operation of control equipment, management of radioactive materials and use of personal protection equipment The work practices and procedures should be reviewed and evaluated periodically to incorporate changes that are necessary due to process modifications or changes in regulatory requirements, or to reflect improvements in radiation safety practices

4.4.1 Access Control

One of the simplest and most effective operational practices that can be used to reduce radiation exposure is to limit personnel access

control is erection of physical barriers preventing access, for exam-

abandoned work areas For areas which may be routinely occupied, the use of signs and other "postings" is appropriate, and routine access should be restricted to personnel required for production and

Areas in which dose or airborne concentration limits may be approached should be designated as requiring special precautions for entry; for example, the yellowcake packaging areas at uranium mills Special work permits should be used to control access to these