Advances and innovations in nuclear decommissioning10 the end state of materials, buildings, and sites restricted or unrestricted release

Advances and innovations in nuclear decommissioning10 the end state of materials, buildings, and sites restricted or unrestricted release Advances and innovations in nuclear decommissioning10 the end state of materials, buildings, and sites restricted or unrestricted release Advances and innovations in nuclear decommissioning10 the end state of materials, buildings, and sites restricted or unrestricted release Advances and innovations in nuclear decommissioning10 the end state of materials, buildings, and sites restricted or unrestricted release Advances and innovations in nuclear decommissioning10 the end state of materials, buildings, and sites restricted or unrestricted release

Advances and Innovations in Nuclear Decommissioning http://dx.doi.org/10.1016/B978-0-08-101122-5.00010-7

10

The end state of materials,

buildings, and sites: Restricted

or unrestricted release?

T Hrncir * ,† , M Listjak * ,‡ , M Zachar * ,† , M Hornacek *

*Slovak University of Technology in Bratislava, Bratislava, Slovakia, †DECOM, Trnava, Slovakia, ‡VUJE, Trnava, Slovakia

10.1 Introduction

Peaceful utilization of nuclear energy inevitably leads to the generation of als containing radionuclides as a result of contamination or the activation process Concentration of these radionuclides in materials, building structures, or at sites is carefully monitored In order to protect the health of workers, people living near nu-clear facilities, as well as the environment, the fundamental safety principles are jointly issued by the international community These principles include the following [1]:

materi-l Optimization of protection Protection must be optimized to provide the highest level of safety that can reasonably be achieved.

l Limitation of risks to individuals Measures for controlling radiation risks must ensure that

no individual bears an unacceptable risk of harm.

l Protection of present and future generations People and the environment, present and ture, must be protected against radiation risks.

fu-Following the aforementioned principles, the Basic Safety Standards (BSS) were issued jointly by the International Atomic Energy Agency (IAEA), Nuclear Energy Agency/Organisation for Economic Co-operation and Development (NEA/OECD), European Commission (EC), World Health Organization (WHO), and other interna-tional organizations BSS covers all three possible situations [2]:

l planned exposure situations,

l emergency exposure situations,

l existing exposure situations.

The concept of the release of materials, buildings, and sites refers to planned sure situations This is in line with the definition of the scope of a planned exposure situation that covers, among other things, the generation of nuclear power, including any activities within the nuclear fuel cycle that involve or that could involve exposure

expo-to radiation or exposure expo-to radioactive material [2]

Dose limits for a planned exposure situation are stated [2]; more specifically, the dose limit relevant for the public represents the annual value of 1 mSv Following the principle of the optimization of radiation safety, dose constraints lower than the afore-mentioned limit are usually applied for a particular activity; for example, in the case

of clearance of materials, the effective dose incurred by any individual owing to the cleared material relevant to the reasonably expected scenarios is of the order of 10 μSv

or less in a year [2] This dose level is based on the concept of trivial radiation risk;

in other words, the dose is so low that risk related to potential detrimental impact on health is negligible

These dose constraints should be followed regardless of the planned end state narios for material clearance, release of buildings, or sites Nevertheless, the decision making process leading toward the selection of the end state represents the crucial point in the clearance scenario development and is essential for conducting the safety assessment, as well as deriving the release criteria and related clearance levels.BSS, as well as many national legislations, stipulate the clearance levels, in other words, concentrations of radionuclides contained in the material, building structure, or site, do not incur a higher effective dose to any individual than the defined dose con-straint value; the associated radiation risk is kept at a trivial or negligible level

sce-These clearance levels are derived according to robust safety assessments, taking into account various possible clearance scenarios There are available guides issued by the IAEA, EC, or the US Nuclear Regulatory Commission (US NRC) for derivation and justification of clearance levels However, clearance levels differ from country to country, and this lack of consistency presents a difficulty in this field

Two concepts are available:

l unrestricted release,

l restricted release.

Concepts vary in the possible further use of the cleared material, released ing, or site Unrestricted release allows any possible further use; in other words, even the reasonable worst-case scenario should be assessed On the other hand, a specific end state is defined in case of restricted release; in other words, just the selected end state scenario is taken into account Different exposure pathways and parameters are relevant for each specific scenario This may have a significant impact on the derived values of clearance levels

build-Recently, the release issue became a topic of high importance regarding incentives for waste management optimization and economical effectiveness Although there are some lessons learned from a few case studies, there is still a lack of experience with restricted release Similarly, there is a need for consistent guides for both unrestricted and restricted release concepts This issue was recognized by the IAEA as well as the NEA/OECD

The IAEA regularly organizes workshops for experts and prepares guides relevant

to this issue Moreover, one of the results of the most recent conference organized

by the IAEA in Madrid (May 2016) devoted to decommissioning and environmental remediation activities recommends the development of international standards and guidance for conditional clearance of materials from decommissioning [3]

NEA/OECD is running the projects devoted to the optimisation of the management

of (very) low radioactive materials and waste from decommissioning, which include works on the issue related to the management of slightly contaminated materials aris-ing from decommissioning

The following sections include up-to-date advancements in the process of releasing materials, buildings, and sites Related basic principles, international recommendations, and guides are gathered, and a brief summary is provided Available options, as well

as case studies relevant for a particular end state of materials, buildings, and sites, are discussed Moreover, lessons learned from case studies are summarized and benefits

or drawbacks connected to particular end state options are outlined A summary of the chapter includes key findings and ideas that may constitute the basis for wider expert discussion about rationales for using an unrestricted or restricted release approach on

a case-by-case basis

10.2 End state of materials

10.2.1 General principles

The decommissioning of nuclear installations represents a complex process resulting

in the generation of large amounts of various waste materials containing different els of radionuclide concentrations (e.g., very low-level, low-level, intermediate-level,

lev-or high-level waste)

The IAEA definition of the waste classes relevant for this chapter are: [4]:

l The very low-level waste classification includes the waste with levels of activity tion in the region of or slightly above the levels specified for the clearance of material from regulatory control.

concentra-l Low-level waste classification is relevant for the waste with activity concentrations higher than the very low level waste, which is suitable for a near surface repository Low-level waste may contain some level of long-lived radionuclides An activity concentration limit value

of 400 Bq/g on average (4000 Bq/g for a particular package) for long-lived alpha emitting radionuclides is adopted in some states (for long-lived beta and/or gamma emitting radionu- clides, the allowable average activity concentrations may be higher and may be specific to the site and disposal facility).

Very low-level waste and low-level waste represent the vast majority in volume of radioactive waste arising from decommissioning On the other hand, this waste contains only a small fraction of the radiological inventory of a nuclear facility The concentration

of particular radionuclides is so low that some of these materials can be, after application

of various techniques, released into the environment Therefore, selection of an optimal way to manage these materials, taking into account, for example, the concept of clear-ance, may be vital for a sustainable, safe, and cost-efficient decommissioning process.Based on BSS, the general criteria for clearance are [2]:

l Radiation risks arising from the cleared material should be sufficiently low as not to warrant regulatory control; there is no appreciable probability of occurrence of scenarios that may result in possible failure to meet the general clearance criteria.

l Continued regulatory control of material would not bring any net benefit; no reasonable control measures would achieve a worthwhile return; in other words, much effort in terms

of reduction of individual doses or reduction of health risks would be needed for minimal improvements of an already good situation.

Following the trivial risk principle (the expected dose is so low that the mental effect of ionizing radiation is considered negligible), the dose constraint for clearance of materials is defined Materials may be cleared if the aforementioned dose constraint is met in reasonably foreseeable circumstances of clearance sce-narios The dose constraint value for the clearance of materials is on the order of

detri-10 μSv or less in a year Addressing the low probability scenarios, a different dose constraint may be used In this case, the individual effected dose must not exceed

1 mSv in a year

To facilitate the clearance process, clearance levels valid for unrestricted lease of material into the environment were developed and provided in the BSS [2] Derivation of these clearance levels was performed based on the robust input parameter database and comprehensive analysis of possible scenarios and relevant exposure pathways In principle, if these clearance levels are met, it is expected that the clearance scenario (even in the case of a worst-case scenario) complies with the release criteria in the form of dose constraint as well, and no further proving or jus-tifying is necessary Moreover, aforementioned clearance level values were adopted

re-by EC and included in the Council directive 2013/59/EURATOM All member states must comply with this directive by February 2018 [5]; in other words, this directive represents the next step toward consistency in the field of material clearance in the European Union

However, an option for development of specific clearance levels is still available In this case, one must develop a specific clearance scenario, define the end state valid for the scenario, develop the comprehensive database of relevant input parameters, justify the specific input parameters and boundary conditions, conduct the safety assessment specific to the scenario, and prove that specific clearance levels are derived appropri-ately following the dose constraint principle

In other words, one must create a robust database and conduct the sive safety assessment relevant for a specific clearance scenario similar to those performed for derivation of clearance levels in BSS Because different exposure pathways and parameters are relevant for specific scenarios, derived clearance levels for this specific clearance scenario may differ from the clearance levels valid for unrestricted use (specific clearance levels may be less restrictive)

comprehen-10.2.2 International guides and recommendations

Several recommendations and guides relevant to the clearance of materials are able The basic documents dealing with the concepts of clearance of materials were issued by the IAEA and EC

avail-In 2004, the IAEA issued a safety guide devoted to the application of the concepts of exclusion, exemption, and clearance [6] The basic principles and recommendations were provided The guide also prescribed values of activity concentration for radionuclides

of natural origin as well as for radionuclides of artificial origin in bulk (i.e., clearance levels) Various aspects of applying these values were addressed The scientific basis and detailed information on derivation of mentioned clearance levels were provided in

another document [7] Clearance levels recommended by the IAEA for unconditional clearance (unrestricted use of materials) were updated via the new BSS [2] in 2014.The EC issued several documents within the “Radiation Protection Series” devoted

to the clearance concept Two types of materials were considered: metals and crete rubble Recommended radiological protection criteria for the recycling of metals from the dismantling of nuclear installations, along with the methodology and models used, are stated in [8,9] Similarly, two other documents [10,11] were devoted to the clearance of buildings and building rubble, providing related methodology and scien-tific bases Specific clearance levels were derived for particular scenarios (restricted use) for metals and building rubble (e.g., clearance values for conditional clearance

con-of metals after application con-of melting were provided) Council directive 2013/59/EURATOM includes the clearance levels for unrestricted use of materials However, this directive encourages the Member States to use the specific values and results from analysis done in documents from the Radiation Protection Series

Besides these guides, robust work was done by the US NRC on radiological ments for clearance of materials from nuclear facilities [12] Dose assessments for various scenarios of recycling and disposal of steel, copper, and aluminum scrap, as well as con-crete rubble, were done; the rationale for selecting input parameters was also provided.Moreover, NEA/OECD issued a publication describing advances in the field of release of radioactive materials and buildings from regulatory control in 2008 [13].Generally, IAEA and EC guidelines recommend the following procedures to de-velop and justify the clearance scenario and derive relevant clearance levels for con-sidered materials:

assess-1 definition of the end state of particular material—either unrestricted reuse or a particular

scenario of restricted reuse;

2 development of the clearance scenario—gathering all necessary input parameters for the

scenario (e.g., source term, exposure time, physical parameters, etc.); defining the boundary conditions and particular activities in the scenario;

3 dose assessment—identifying the relevant exposure pathways for particular activities and

calculation of effective dose incurred to the critical individual because of the clearance of material and its reuse according to the defined end state;

4 derivation of clearance levels for radionuclides of concern using the results of dose

assess-ment and defined dose constraints.

Although these aforementioned recommendations are available, the regulatory framework for clearance of materials still differs from country to country

10.2.3 Case studies

The applications of the concepts of clearance depend strongly on the economic, nical, and nontechnical aspects in each country, as well as on the legislative frame-work Thus, a general overview providing the status of the application of the clearance concept in selected countries is given in Table 10.1

tech-Further information of the relevant examples regarding clearance of materials is given in the following sections

10.2.3.1 Belgium

Practical experiences in clearance of materials is from the decommissioning process

of a small pressurized water reactor BR3 (electrical output 10.5 MW, operation in 1962–87) and open pool research reactor Thetis (power of 150 kW, operation in 1967–2003) In the case of both reactors, more than 90% of the materials are clearable (92% from Thetis and 91% from BR3) [14]

Another example is decommissioning of a former reprocessing plant Eurochemic (site BP1), which was in operation from 1966 to 1974 From the start of decommis-sioning in 1989–2014, 1239 tons of metallic materials were released into the environ-ment for unrestricted use (about 70% of the entire metal inventory) This involved segmentation, blasting, and melting of the metals [15]

State Clearance concept in the national legislative framework

Table 10.1 Clearance of materials in the countries—general

overview

10.2.3.2 Czech Republic

An example of clearance of materials is from the activities connected with tion of environmental liabilities in ÚJV Řež, a.s., where all RAW stored at the storage area Červená skála was removed In total, 4377 kg of waste material has been cleared; another 16,250 kg of this material has already been monitored for compliance with clearance levels and is ready for unconditional clearance [16]

10.2.3.4 Germany

Because of the current lack of final disposal options for radioactive waste, Germany has

a well-developed concept of clearance of materials To meet the requirements for release

of the materials from regulatory control, the following operations can be carried out [18]:

l Storage (e.g., in Interim Storage North at Greifswald site)—decay storage However, this approach is very sensitive to possible change of the clearance limits.

l Decontamination (e.g., in a central active workshop located in a separate building at the Greifswald site).

Examples of clearance of materials are listed as follows [19,20]:

l Nuclear Power Plant (NPP) Greifswald—a total amount of cleared material of about 94,000 tons (about 26,000 tons of concrete and 68,000 tons of plant components).

l NPP Stade—from 132,000 tons of materials from nuclear area:

l 97.3% (128,500 t) controlled release;

l 0.4% (500 t) controlled reuse and recycling;

l remaining 2.3% (3000 t)—radioactive waste.

Besides the chemical and mechanical decontamination techniques, the ination of the metals can be realized by melting technology as well In Germany, this

decontam-is carried out in the CARLA melting facility From 1989 to 2009, 25,000 tons of metal were processed, 9000 tons could be cleared, and 14,500 tons were recycled within the nuclear industry (e.g., for production of shielding) [21]

In the German legislative framework, eight clearance options are defined; four tions are available for the unconditional clearance [18]:

op-l unconditional clearance of (solid or liquid) substances that may later be reused, recycled, or disposed of;

l unconditional clearance of rubble and excavated soil of more than 1000 Mg per year that after clearance may be used for any chosen purpose, for example, for the backfilling of ex- cavations, such as road bedding, etc.;

l unconditional clearance of buildings that afterwards may be demolished or also be reused;

l unconditional clearance of soil areas that may subsequently be used for any purposes, for example, for the construction of houses and apartment buildings, industrial buildings, etc.

In the case of clearance for a specific purpose, in other words, conditional clearance (in which the first step is exactly specified) has four clearance options [18]:

l clearance of solid substances for disposal in a (conventional) landfill with masses of up to

100 Mg/a and up to 1000 Mg/a, respectively;

l clearance of (solid or liquid) substances for removal in an incinerator with masses of up to

100 Mg/a and up to 1000 Mg/a, respectively;

l clearance of buildings for demolition, with any conventional use of the buildings prior to their demolition being impermissible;

l clearance of scrap metal for recycling by smelting in a conventional melting facility, for example, foundry, steel works, etc.

10.2.3.5 Slovakia

Slovakia has several projects where the clearance of materials is carried out An ple is the clearance of underground tanks at A1 NPP in Jaslovske Bohunice (former tanks for CO2) In this case, about 735 tons of metals can be released to the environ-ment [22] Another example is unrestricted release of concrete underground tanks at A1 NPP site, which were then filled with clean soil [23] During the decommission-ing process of underground tanks, bulk volumes of slightly contaminated soil were excavated Based on the measurement conducted at a special facility (as shown in

be disposed of at repository for very low-level radioactive waste

Fig. 10.1 Facility for measurement of contaminated loose materials.

Similarly, the significant amount of cleared materials can be expected during ing decommissioning of V1 NPP in Jaslovske Bohunice.

ongo-10.2.3.6 Sweden

The metallic radioactive waste can be treated in the melting facility of Studsvik erated from 1987) Until 2014, about 27,700 tons of scrap metal (carbon and stainless steel), 800 tons of aluminum, and 400 tons of lead were treated [24] Examples of the quantities of cleared materials [24,25] were provided, as follows:

(op-l 600 tons in 2004 cleared for disposal at municipal landfills;

l 764 tons of melted metal cleared for recycling in 2010;

l approximately 10,000 tons of ingots cleared for restricted use produced from 2005 to 2012.

10.2.3.7 France

According to French legislation, the recycling or reuse of materials, even if very slightly radioactive, is allowed exclusively in the nuclear industry (waste containers, biological shielding in waste packages, etc.) This law means large quantities of ma-terials that cannot be cleared are generated and must be disposed of as radioactive Therefore, the concept of disposal of very low-level waste has been developed, and the repository in Morvilliers is used for this operation

French legislation prescribes the zoning approach; that is to say, waste zoning is implemented within nuclear installations in order to segregate areas where waste can-not a priori be contaminated or activated and areas where waste contains or may con-tain added radionuclide concentrations This approach has several benefits, but it also has a major drawbacks

l practical way to dispose of very low-level waste that does not meet clearance levels.

The main drawback of the concept is that it makes it difficult to clearly define whether the materials are radioactive or conventional (nonradioactive) Moreover, this concept may not be suitable for countries with small or developing nuclear sectors Although only few nuclear installations are located in these countries and lower quantities of very low-level waste are expected, the requirement to have suf-ficient disposal capacity (often significant volumes are necessary) for very low-level waste represents a challenging issue

10.2.4 Discussion

As it was mentioned earlier, recommended clearance values enabling the unrestricted reuse of materials are available Moreover, thanks to the Council directive, the next

step toward consistency in the field of unconditional clearance of materials already exists at least in the European Community.

However, there is still a lack of consistency in the clearance concept, and the islative framework for clearance differs from country to country Moreover, there are only a few examples of utilization of the conditional clearance concept (e.g., appli-cation of metals clearance after melting in Germany) Conditional clearance seems to

leg-be interesting from the economic point of view and may lead to optimization of the use of disposal capacities Although principles for derivation of specific clearance values are well known, and procedures for derivation are available in the guides, it would be useful to update these guides (many of them were issued more than 10 years ago) Furthermore, guides focused particularly on conditional clearance may be ben-eficial, especially for countries with limited budgets and with a lack of waste disposal capacities

Following the waste management hierarchy, disposal as radioactive waste should

be the last option The application of different approaches leading to optimization of waste management is highly desirable from a sustainability and economic point of view The clearance of materials, both for restricted (conditional clearance) and unre-stricted (unconditional clearance) use, along with recycling of materials or equipment, represents a promising option, keeping in mind the required level of safety

Because a particular scenario is assessed in the case of conditional clearance, higher specific clearance levels may be achieved However, much effort is required

to develop the safety case for a particular scenario, derive the specific clearance levels, and analyze the impact on the waste management system, including the optimization of the use of disposal capacities Moreover, the overall assessment

of a particular conditional clearance scenario should address the economic aspects

in order to prove that scenario is feasible and that would provide a worthwhile return

Another option is recycling and reuse of the materials and equipment within the nuclear sector Application of this process may save significant financial resources In the United Kingdom, the Nuclear Decommissioning Authority cre-ated an asset transfer scheme in order to advertise unwanted items or seek re-dundant equipment from other nuclear sites Reusing and recycling across the Nuclear Decommissioning Authority's estate is expected to save £15 million over 8 years [26]

Guides covering the economic aspects and other nontechnical aspects (e.g., holder involvement) of the conditional clearance or recycling of materials within the nuclear sector would be useful as well

stake-Alternatively, disposal of slightly contaminated materials at the repository for very low-level waste is preferred in some countries in order to avoid complex clearance procedures and verification of compliance with clearance criteria

Therefore, a detailed study addressing the safety, technical, and economic aspects

of particular options is crucial for the selection of the optimal option for the ment of materials containing very low concentration of radionuclides

manage-10.3 End state of buildings

10.3.1 General principles

The selection of a particular end state of buildings has a significant impact on their release criteria Possible principal end state options are the following:

l demolition of buildings;

l release of buildings for unrestricted purposes;

l release of buildings for restricted purposes.

In the case of planned building demolition, it is necessary to bear in mind that generated building rubble is movable material, and thus the rubble should comply with the criteria valid for material clearance In other words, the effective dose for an individual valid for reasonably foreseeable circumstances of clearance scenarios is of the order of 10 μSv or less in a year (see general principles for materials clearance for further details)

However, if it is planned that building structures remain standing at the end of decommissioning, it is possible to treat these buildings as a part of the site to be released This means that it is possible to apply the site release criteria and include the residual radioactivity contained in the building structures to the site source term Based on the IAEA recommendations, the dose constraint valid for release of the site is up to 300 μSv in a year (for further details, see general principles for site release) [27]

10.3.2 International guides and recommendations

There are a few guides addressing the steps in the release of buildings, as well as the derivation of clearance levels EC issued several documents within the radiation protection series Two documents [10,11] were devoted to the clearance of buildings and building rubble and related methodology and scientific bases Specific clearance levels were derived for three scenarios relevant for building release [10,11]:

l Reuse of buildings After the clearance process, the buildings can be used for nonnuclear purposes or be demolished; the clearance level was expressed as the total activity in the structure per unit surface area (the typical process of the final radiological survey along with the measurement mesh is depicted in Fig. 10.2 ).

l Demolition of buildings Buildings are demolished resulting in the generation of rubble; the clearance level was expressed as total activity in the structure per unit surface area;

l Specific clearance criteria for building rubble The clearance level was expressed as mass-specific activity.

Another useful guide is the Multi-Agency Radiation Survey and Assessment

of Materials and Equipment manual (MARSAME) [28] MARSAME is a plement to the Multi-Agency Radiation Survey and Site Investigation Manual (MARSSIM) [29] and provides a detailed approach for planning, performing,