Advances and innovations in nuclear decommissioning9 decommissioning after a severe accident

Advances and innovations in nuclear decommissioning9 decommissioning after a severe accident Advances and innovations in nuclear decommissioning9 decommissioning after a severe accident Advances and innovations in nuclear decommissioning9 decommissioning after a severe accident Advances and innovations in nuclear decommissioning9 decommissioning after a severe accident

Advances and Innovations in Nuclear Decommissioning http://dx.doi.org/10.1016/B978-0-08-101122-5.00009-0

9

Decommissioning after a severe

accident

C.A Negin * , M Božik † , D Stelmakh ‡ , H Rindo §

*CANegin&Associates, Washington Grove, MD, United States, †Nuclear and

Decommissioning Company, plc., Bratislava, Slovakia, ‡Chornobyl NPP, Slavutich, Ukraine,

§Institute of Applied Energy (IAE), Tokyo, Japan

9.1 Introduction

The conditions of nuclear facilities following a severe accident present difficult lenges caused by the combination of (a) uncontrolled release and spread of radioactive material and (b) damage to structures, systems, and components (SSC) as a result of exposure to high pressures and temperatures in areas normally protected by contain-ment and system barriers The breach of containment barriers can cause major impacts

chal-to and influence the course of decommissioning Postaccident abnormal conditions are characterized by many uncertainties and unknowns (UUs) that are key factors that impact strategies, methods, and techniques for subsequent decommissioning

In the long-term, there are three phases typically associated for dealing with the termath of a severe accident These are (1) stabilization, (2) recovery, and (3) final de-commissioning Note that “final” decommissioning is used to indicate the time when the facilities can be dealt with by methods like standard decommissioning practices, whereas decommissioning alone refers to all the phases in general Stabilization refers

af-to the immediate aftermath of a nuclear accident; it controls conditions so that impacts af-to the environment and general public are minimized Stabilization can involve repair and restoration of operating and structural functionality to achieve this minimum impact state Recovery entails the planning and implementation of activities to limit, and subsequently reduce, the extent of abnormal conditions and prepare the plant to achieve a longer term, safer configuration Recovery can be viewed as precursor to final decommissioning.There is no clear-cut schedule milestone between any two of the three above-mentioned phases; they can overlap UUs are generated by the accident and its evo-lution, and they may initially be recognized, faced, and dealt with during both the stabilization and recovery phases For example, treatment of liquid waste initiated during the recovery phase may continue well into the decommissioning phase The schedule will evolve as access to SSCs is gained, either manually or with remotely operated equipment Such access will be needed to identify the types and magnitude

of actual and potential challenges Access will allow detailed characterization (such

as visual display of physical conditions and radiological contamination and intensity) that is essential for planning of work scope, schedule, and cost estimates Such plans will evolve and change as understanding of conditions becomes better known

Each severe accident is unique regarding the initiating cause and resulting ditions Because of unpredictable conditions and evolution of a severe accident, it

con-is difficult to define specific UUs that will be encountered during stabilization and recovery of a facility after a severe accident The best that can be done to analyze UUs

is to define categories and provide specific examples based on the experience of severe accidents such as A1 Bohunice, Three Mile Island Unit 2 (TMI-2), Chernobyl, and Fukushima Daiichi, which are described in this chapter

order from 1952 to 2011 [1] In this table, the INES scale [2] indicates the severity of the accident

9.2 Developments on nuclear facilities’ shutdown,

recovery, and decommissioning after an accident

This section describes some of the activities at facilities that have undergone ous accidents The report, “Experiences and Lessons Learned Worldwide in Cleanup and Decommissioning of Nuclear Facilities in the Aftermath of Accidents” [3], is a

seri-Plant (year) INES scale Country Primary cause

St Laurent (1968) gas-cooled,

graphite moderated

Lucens (1969) experimental

gas-cooled, heavy water moderated

blockage Jaslovské Bohunice, A1, (1977)

gas-cooled, and heavy water

moderated

blocked fuel channel Three Mile Island (1979) PWR,

light water-cooled

and relief valve stuck open

Chernobyl (1986) RBMK,

water-cooled, and graphite moderated

operating procedures PAKS (2003), PWR (Within a

cleaning vessel outside of the

reactor)

delay Fukushima Daiichi (2011), BWRs,

and light water-cooled

Table 9.1 Nuclear reactor fuel damage accidents

comprehensive description of the total range of on-site activities following severe accidents This reference includes subjects of stakeholder communication and involvement, planning, stabilization, characterization, damaged fuel management, final decommissioning and site remediation, and accident waste management This reference combined the experience from the cases described in this chapter and others.Descriptions of accidents and immediate stabilization phases described in this chapter are included to establish the background The bulk of this section is given to planning and implementation of recovery and planning for final decommissioning Activities in this section range from those closer in time to the accident (mostly, recovery)

to those leading to the final decommissioning In each case, these activities depend on the specific circumstances of the accident and the time elapsed since its occurrence

9.2.1 Fukushima Daiichi

9.2.1.1 The accident

At 2:46 p.m on Mar 11, 2011, the Tohoku-Chihou-Taiheiyo-Oki Earthquake affected

an area that ranged from off-shore of Iwate Prefecture to the Ibaraki Prefecture All the operating reactors were automatically shut down Distance from the Fukushima Daiichi Nuclear Power Station (NPS) to the epicenter was 178 km

At the Fukushima Daiichi NPS, the subsequent arrival of the tsunami, which was one of the largest in history, caused flooding of many cooling seawater pumps, emergency diesel generators, and power panels There were station blackouts for Units 1–5, and all the cooling functions using AC power were lost in these units Consequently, the fuel in each unit was exposed without water immersion or flood-ing, causing damage to the nuclear fuel cladding Radioactive materials in the fuel rods were released into the reactor pressure vessels The chemical reaction be-tween the fuel cladding (zirconium) and steam caused the generation of a substan-tial amount of hydrogen

Later, in Units 1 and 3, explosions of the hydrogen leaking from the primary tainment vessels destroyed the upper structures of their reactor buildings Another explosion occurred at the upper structure of the reactor building in Unit 4 where all the fuel had been removed from the reactor well before the earthquake and stored under water in the spent fuel pool The Unit 4 fuel was not affected by the loss of cooling

con-In Fukushima Daiichi Units 5 and 6, one of the emergency diesel generators for Unit 6 was in operation By connecting a power cable to Unit 5, cooling water was supplied to the cores of both units After the restoring the residual (decay) heat re-moval function a, Units 5 and 6 achieved cold shutdown

9.2.1.2 Examples of stabilization objectives continuing into the

recovery phase

Some of the stabilization phase for Fukushima Daiichi activities and their near-term objectives are shown in Table 9.2 These immediate challenges were faced by the plant operators for which the objectives were successfully achieved to allow moving on to the recovery phase

Of those listed in the table, the continuation of the activities for contaminated water and managing radioactive wastes are further described It is important to understand that these two activities are only two of many not addressed in this report.

9.2.1.3 Processing the contaminated water

Prior to 2016, about 400 m3 of groundwater flowed into the accident facilities every day, and it became contaminated when contacting the fuel debris and contaminated surfaces, then passing into the turbine building In addition, water for the cooling of the nuclear reactor (fuel debris) requires a 400 m3/day Therefore, the contaminated water flowing out from turbine building was about 800 m3/day This quantity of con-taminated water then requires cleanup processing

Cesium-137 is a primary radionuclide of concern in the contaminated water Cesium

is removed by two systems: the KURION (backup system) and SARRY (used for mal operation) After that, the contaminated water is introduced into the desalinization equipment (Reverse Osmosis membrane) to remove the salt for reuse of 400 m3/day About 400 m3/day of surplus water is stored in medium- to low-level tanks on the site

nor-Stabilization activities Objective

Cooling of the fuel and fuel debris Cold shutdown with temperature below 100°C within

the reactor system and below 65°C in the spent fuel pools with the ability to maintain those conditions Monitoring of plant conditions The ability to detect increases in temperature,

pressure, and radiation are established with instruments

Criticality prevention Increases in reactor or fuel pool temperatures are

detected and means are in place for actions should the increase be attributed to neutron criticality Ventilation and hydrogen control Significant increases in concentration or

accumulation of hydrogen within building spaces and reactor systems are prevented

Airborne concentrations of radioactivity are controlled in spaces where humans are working Reactor building structural stability The reactor buildings' structures have been repaired

and reinforced to provide safe enclosure for future work to remove the fuel in the pools

Containment of scattered

radioactive materials

Radioactive materials on the site outside of buildings are prevented from windblown distribution off-site Site boundary monitoring is in place to indicate if there are increases being transported off-site

processed to reduce radioactivity and/or is being stored

Radioactive wastes Radioactive waste external to buildings has been

collected and is stored or covered

Table 9.2 Some Fukushima Daiichi stabilization objectives

The Advanced Liquid Processing System (ALPS) was then put into operation and can remove most nuclides to concentrations that are sufficiently low, except for tritium Three sets of ALPS are installed at the site; however, a more advanced system will

be installed to reinforce the processing capacity The contaminated water treatment system is shown in Fig. 9.1

Cesium-137 in the contaminated water of the reactor vessel reaches equilibrium

in approximately 1.5 years after an accident Future management of cesium will be primarily to continue removal of relatively small amounts that will be released while retrieving fuel debris

9.2.1.4 Management of tritium

Tritium is a naturally existing radionuclide, and the background levels in the ment are about 0.01 Bq/g Because the inflow of groundwater is extremely low, the content of tritium is in equilibrium with the leaching from the fuel debris The half-life

environ-is 12.3 years and the biological half-life environ-is 12 days

Tritium cannot be removed with the installed contaminated water processes When the leak points of the reactor pressure vessel are repaired and an inflow of groundwater and an outflow of contaminated water are prevented, a closed loop will be established for cooling the fuel debris If all tritium was accumulated in this loop, the radioactivity concentration of tritium is estimated to be less than 1 × 105 Bq/mL The remaining tritiated water will be stored in the tanks with the processed water [4]

Reactor cooling water:

Reuse

Advanced liquid processing system (ALPS)

Water storage tanks Test operation currently conducted

Desalinization equipment

Medium- to low-level

tanks

Cesium removal devices (1) Areva (France)

There are several methods to remove molecular tritium from water, but any of these methods are not realistically feasible in view of the very low concentrations and with current removal technologies If such separation were to be possible, it is thought that

a risk of the pollution by leaks would be big as for storing a large quantity of processed water containing highly concentrated tritium for a long-term

Tritium is a naturally existing nuclide If the concentrations at Fukushima become close to background levels, it will be low enough such that the environmental risk of releasing it may be acceptable However, before that can be considered, it is important for the stakeholders to understand this process

9.2.1.5 Preventing inflow of groundwater

Preventing the inflow of the groundwater into the site is a major challenge Three methods as described below are being put in place to prevent groundwater intrusion.Bypassing ground water flowing to the sea side from the mountainside is achieved

by pumping and diverting around buildings Changing the passage of the water duces the water level around the building To prevent contaminated water within the buildings from flowing out, reducing the flow volume of the water into the building

re-is increased step-by-step Thre-is method reduces the groundwater inflow from about

400 m3/day to about 100 m3/day

Subdrains existed prior to the accident to prevent of inflow of groundwater into the basement of the buildings and to prevent a buoyancy effect to act on the buildings This system performance before the accident pumped up about 850 m3/day of ground-water The subdrains were rendered unusable by the tsunami; however, a restoration plan is under consideration to control the inflow of the groundwater into the building Radioactive material released in the atmosphere can result in contaminated rainwater water that may flow in the subdrain pit Therefore, a judgment for processing the subdrain water to bypass the site depends on inspection of the system and characteri-zation of the collected water

Installation of a landside impermeable wall surrounding Units 1–4 can block water inflow A frozen soil method has been selected and is in the process of testing

ground-9.2.1.6 Characterizing the radioactive solid waste

The solid waste of Fukushima Daiichi NPS is different from solid waste from tional nuclear power plants Common characteristics of the Fukushima Daiichi solid radioactive waste are the following:

conven-● Failed fuel elements were scattered in the reactor vessel and/or relocated out of the reactor pressure vessel into the primary containment vessel.

● Most forms of contamination are surface contamination except for activated materials and are captured internally by melting during the accident.

● Data for the locations and quantities of the radionuclides, particularly data of long-life nuclides, are limited.

The waste contains relatively large amounts of fission product radionuclides from the nuclear fuel, activation radionuclides from the reactor core components, salt from

the emergency use of seawater, and other hazardous materials resulting from the nami flooding Radioactive solid waste including such materials has various technical issues to be solved for packaging and disposal.

tsu-Characterization of the radioactive solid waste is very important for future mantling of the plant It is expected that the nuclide composition of each waste and features of contamination level can be estimated to some extent by the end of Mar

dis-2017 Techniques to analyze nuclides difficult to measure and inventory evaluation techniques will be developed Even at this point, however, data on the characteristics

of the waste is still limited; therefore, characterization will be continued Based on this information, the applicability of processing and disposal techniques will be eval-uated In addition, the operation of new nuclide analysis facilities will begin in 2018

to accelerate waste analysis Because the schedule has been delayed It will start the operation in this year

Based on the information gathered by the end of Mar 2017, a report on the sic concept on processing/disposal of wastes” will be compiled in Mar 2018 and be used to begin a regulatory study Continuing beyond Mar 2018, a future radioactive material analysis and research facility will be used to characterize wastes, accumulate analysis data using development technologies, and improve the accuracy of inventory evaluation As a result, a processing facility will be installed in the site around after Apr 2021, when production-level packaging of waste is expected to begin

“ba-9.2.1.7 Managing the radioactive solid waste

The amount of the radioactive solid waste generated directly during the accident is shown in Table 9.3 This is the amount currently being kept and managed on-site.Estimating the precise volumes for future waste management planning is very diffi-cult because in addition to current knowledge, the amounts of various waste types will depend on the decommissioning methods and efficiencies during fuel debris removal

Category Storage method Quantity (m 3 ) Storage capacity

Debris less than

0.1 mSv/h

Debris 1–30 mSv/h Temporary storage

facility/tent and containers

Tree branches and

leaves

Temporary storage for trimmed trees

Table 9.3 Summary of the waste storage and their capacities (as of the end of 2015)

and, ultimately, the demolition of facilities and site cleanup This will only be known

as the scenario evolves and the many current uncertainties are resolved

In addition, during future operations of ALPS, a large amount of secondary tive solid waste will be generated [5] Large amounts of iron oxide sludge and carbon-ate sludge are especially generated as a secondary radioactive solid waste; however, it

radioac-is currently difficult to take samples to analyze the radionuclides for structural lems These radioactive wastes should be analyzed to know the contained nuclides for future processing/treatment It is necessary to reduce the volume of radioactive solid waste by incineration of burnable waste etc because about 3/4 of the storage area has already been occupied by radioactive solid waste For processing/treatment and dis-posal of the radioactive solid waste, radionuclide analysis should be accelerated The new analysis facilities are going to be installed in Fukushima, but the analysis method

prob-is developed by JAEA Analysprob-is time prob-is shortened by 1/3, compared with a tional analysis system [6] Based on these results, the mid- and long-term roadmap in-dicates that it is possible to set up a general plan of processing/treatment and disposal

conven-of radioactive solid waste by the end conven-of Mar 2018 The roadmap also indicates that it

is possible to get the technical prospect for safety measures for treatment and disposal

of the radioactive solid waste by 2021

Various options not only in terms of technical perspectives but also in terms of social perspectives are possible for treatment and disposal of radioactive waste As for the end date of the decommissioning, international expert cooperation is necessary, and relevant information should be shared among stakeholders In radioactive waste disposal, the assessment of disposal system barrier performance is necessary with radiotoxicity and chemical form; and the physical and chemical properties of solidi-fication need to be considered As well as conventional disposal forms, new disposal forms should also be considered

9.2.1.8 Fukushima’s path forward

Current activities toward decommissioning are steadily progressing Radioactive waste processing/treatment and disposal and decommissioning of Fukushima Daiichi NPS are long-term and wide ranging works and should be performed while keeping

in mind stakeholder involvement Optimizing the entire process through appropriate management and flexibility per the situation are very important in future activities.Before dismantling the facilities, the fuel debris should be removed from the reac-tor systems The removal method of the fuel debris will be decided upon investigation

of the status of the pedestal, fuel debris, and the result of various R&Ds

9.2.2 Chernobyl NPP decommissioning and Shelter Object

transformation into an environmentally safe system

The Chernobyl Nuclear Power Plant (Fig. 9.2) was commissioned in 1977 with four water-cooled, graphite moderated RBMK-1000 reactors Unit 4 was destroyed in the

1986 accident The reactor core of Unit 4, safety systems, and physical barriers were destroyed (Fig. 9.2, left) After 6 months, the large steel and concrete structure Shelter

Object (SO) covering the nuclear reactor No 4 building was constructed (Fig. 9.2, right) The current status and consequences of the Chernobyl accident can be reviewed

in Refs [7] and [8]

Following the accident, Units 1, 2, and 3 operated until they were shut down tween 1991 and 2000 Shutdown was in accordance with the arrangements between G7 governments, the Commission of the European Communities, and the Government

be-of Ukraine

The Chernobyl NPP is located within an exclusion zone area contaminated with long-lived radioactive contaminants from the 1986 accident Considering there are no prospects for constructing new energy and other national economy facilities on-site, it has been judged to be unreasonable to perform decommissioning to a greenfield end state The plan for long-term storage is described later in this chapter

9.2.2.1 Stabilization and recovery activities

In the years since the accident, several important stabilization activities have been completed or are in progress Some of these are as follows:

● All the spent nuclear fuel, including damaged fuel, has been removed from Units 1, 2, and 3

It is stored underwater in a pool within a storage facility.

● Preparations were completed and the authorization to perform the final shutdown and vation stage was obtained in 2015 The main objective of this stage is to establish the condi- tion at Units 1, 2, and 3 for their long-term safe enclosure under surveillance with minimum resource consumption.

preser-● Activities on dismantling of structures external to the nuclear reactor systems and ponents not affecting the safety and not needed for work at a later stage of decommis- sioning are in progress Equipment totaling 9200 tons were dismantled, for which 90%

com-of the metal was decontaminated and released from regulatory control The remainder was disposed as radioactive waste Activities associated with the dismantling of Turbine Hall-2 equipment that began in 2016 are expected to dismantle another 20,000 tons of metal through 2020.

● The ChNPP cooling pond decommissioning is underway The ChNPP cooling pond is an artificially created water body with an area of 22.9 km 2 The operational water level was

7 m higher than the water level in the Prypiat River It was contaminated with radioactive contaminants from the accident The cooling pond is decommissioned by terminating water input and allowing the water level to lower naturally Radiation and environmental monitor- ing of the cooling pond decommissioning are being performed.

Fig. 9.2 View of the Chernobyl nuclear power plant today.

9.2.2.2 Recovery infrastructure

A significant part of the infrastructure for the ChNPP decommissioning is conducted within the framework of material and technical assistance to Ukraine from the interna-tional community These include the following:

● Industrial Complex for Solid Radioactive Waste Management (ICSRM)—activities to pare for commissioning are in progress (scheduled commissioning:2017).

pre-● Liquid Radioactive Waste Treatment Plant (LRTP)—construction was completed In 2014, a separate permission for LRTP operation was obtained.

● A Complex for Manufacturing Steel Drums and Reinforced Concrete Containers for active waste storage and disposal (CMD and C RAW); the facility began operation in 2012.

radio-● The Interim Dry Storage Facility for Spent Nuclear Fuel (ISF-2) has a scheduled sioning for 2017 This will eliminate the need for the current wet storage.

commis-● Facility for Release of Materials from Regulatory Control—a contract for its construction is planned for 2017.

9.2.2.3 Project for transforming the SO to an environmentally

safe system

Currently, works on turning the SO into an environmentally safe system are an sential part of activities being implemented at the ChNPP site A State Specialized Enterprise, “Chernobyl NPP” was established for comprehensive solution of problems with the Chernobyl NPP Unit’s decommissioning and the SO transformation The strategy for the transformation of the SO into an ecologically safe system is achieved through the implementation of three main stages of progression shown in Fig 9.3 Stage 1, the project for the stabilization of shelter building structures, was completed

es-in 2008 This ensures sufficient safety through 2023

Stage 2 is underway It involves creating additional protective barriers and tion for retrieval of fuel containing materials (FCM) and high-level waste (HLW) The New Safe Confinement (NSC) (Fig. 9.4) is a protective structure with a complex of tech-nological equipment for the removal of FCM from the destroyed Unit 4 of the Chernobyl NPP, radioactive waste management, and other systems These will transform this unit into an environmentally safe system and ensure the safety of personnel, the population, and the environment The main building consists of the arch structure with a 257-m span from north to south, a height of 108 m, and a length of 150 m The NSC structure is being

prepara-Stage 1

Stabilization

Stage 2

Construction of the confinement and preparation for retrieval of FCM and HLW

Stage 3

Retrieval of FCM and HLW from SO SO decommissioning

Fig. 9.3 Transformation of the Shelter Object into ecologically safe system.

constructed near the SO Upon completion, the NSC structure was moved in November

2016 to its final location above the SO where outfitting of the internals equipment will

be conducted and commissioned

The completion of the second stage is scheduled for 2023 after dismantlement of the SO’s unstable structures (Fig. 9.5) This will provide conditions for further activities related

to SO transformation The greatest hazard from the SO for the environment and the people

is represented by the FCMs generated during the accident Today, it is considered that the removal of the FCM stored inside the SO and its transfer into a controlled state are the main conditions for ensuring the SO’s safe status This task must be solved at the third stage of the strategy within the NSC’s lifetime (100 years) A tentative overall schedule (Fig. 9.6) shows the key objectives for transforming the SO into an Environmentally Safe System

9.2.2.4 Construction of the NSC

Preparation for NSC construction included cleaning-up and leveling of the area, ration of trenches for constructing the foundations of the NSC erection, transport and service areas, as well as an erection area for preassembling the arch structures

prepa-To ensure clearance for the arch sliding into position, it was necessary to construct

a new ventilation stack of ChNPP Generation 2 and to dismantle the existing lation stack The new stack was completed in 2012, including works associated with

venti-Fig. 9.5 A view of the postaccident Unit before and after construction of the Shelter Object Fig. 9.4 Perspective of the new safe confinement.

installation of external equipment (fire protection, radiation monitoring systems, etc.) Removal of the existing stack was carried out under severe radiation conditions; it was completed in Nov 2013.

Assembling of the main arch structure began in Apr 2012 (Fig. 9.7) The west and east halves of the Arch were fully connected on Jul 24, 2015

29 November, 2016 the NSC slid into place thus the successful enclosure of the heavily damaged Unit 4 at Chernobyl was completed A system of hydraulics was employed to move the arch that weighs 36,000 metric tons and now the New Safe Confinement is the largest man made object ever built for movement on land (Fig. 9.8) Installation of techno-logical equipment is being performed The NSC commissioning is planned for Nov 2017

9.2.2.5 Importance of the NSC

The importance of the NSC is stressed by the event that occurred on Feb 12, 2013 Partial failure of the wall slabs and light roof of the Unit 4 Turbine Hall occurred at the

structure of the SO and there was no violation of limits and conditions of the SO’s safe

Geological repository construction FCM removing and disposal NSC operation

2116

Fig. 9.6 Tentative schedule for implementing the SO transformation strategy.

Fig. 9.7 Beginning and near completion of one half of the main arch structure.

Fig. 9.8 Installation of process equipment.

Fig. 9.9 Collapse of structures at the Shelter Object (area of collapse is shown in the white circles).

operation No changes occurred in radiation at the ChNPP industrial site and within the exclusion zone There were no injuries However, this indicates the process of the

in 1956 and the nuclear plant began construction 2 years later (see Fig. 9.10) The KS

150 reactor was designed in the Soviet Union and built entirely in Czechoslovakia The heavy water moderated reactor used carbon dioxide for coolant; the plant’s elec-trical output was rated at 150 MW Postaccident management of A1 can be reviewed

in Refs [9] and [10]

The discussion of A1 in this section is based on the timeline shown in Fig. 9.11 that illustrates operations and shutdown through 1995, preparation for decommissioning through 1999, decommissioning activities to the present (2017), and plans through

2033 The following discusses the decisions related to the timeline and planning for the future

Fig. 9.10 The A1 NPP during the construction.