The government had need of a guide to the methods

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1 5Protection and environmental synergies 5 2 The management of industrial sites potentially contaminated with radioactive materials A. OUDIZ (IRSN) B. CESSAC (IRSN) J. BRENOT (IRSN) J.-P. MAIGNE (IRSN) P. SANTUCCI (IRSN) The government had need of a guide to the methods of dealing with sites potentially contaminated with radioactive materials 1 and the production of such a guide was entrusted to the Institut de Radioprotection et de Sûreté Nucléaire (IRSN). In order to provide a framework of consistent methods applicable to all contaminated sites, it was stipulated that the new guide should adhere as closely as possible to the procedures specified for dealing with sites contaminated by chemical substances 2. The aim was to provide a reference document that could be used by all parties to enable a dialog to take place based on a common set of data. The guide is targeted at all organizations working on potentially contaminated sites, including national, regional and local government, consultants, insurance companies, manufacturers, and all types of associations involved in the design, construction and operational monitoring of the sites. The guide is available on IRSN website 3. Methodology A STRUCTURED APPROACH The guide describes a procedure consisting of six steps. 1. Removal of doubt. This consists of a short investigation based on measurements of radioactivity in the buildings and on the soil that may have been contaminated, including γ radiation and the associated dose, using specific α, β or γ sensors as appropriate. 2. Pre-diagnosis. The purpose of this stage is to identify and evaluate the actual or potential danger of radiological exposure of persons on and around the site in order to determine the initial protective actions needed in the short term. This normally involves an enquiry and preliminary site visit including the buildings and the immediate environment. 3. Initial diagnosis. This step consists of a survey of the condition of the site and its buildings in terms of past human activity (historical analysis), the vulnerability of the environment (soil, air, and underground and surface water), and a radiologi- Cover of the Guide méthodologique. 1 - These are sites on which industrial or research activities have been carried out in the past involving the use of radioactive materials. Sites of nuclear facilities, either in operation or undergoing decommissioning, are excluded from the scope of the guide. References 2 - DPPR, BRGM, Gestion des sites (potentiellement) pollués. Les outils de cette gestion: le prédiagnostic, le diagnostic initial (étude des sols), l évaluation simplifiée des risques, Issue 1, Oudiz A., Cessac B., Brenot J., Maigne J.-P., Santucci P, Gestion des sites industriels potentiellement contaminés par des substances radioactives, Guide méthodologique, 175

2 Even when all the steps appear to be indispensable, the effort devoted to each should be proportional to the risk. 1 - B. Cessac, CERISE, Code d évaluations radiologiques individuelles pour des scenarios en entreprise et dans l environnement. Technical appendices updated IRSN/DPRE/SERGD Report No. 96/10, ( cal characterization of the site (surface mapping and initial in-depth investigations, and measurements of the radioactivity of the water, vegetable and animal products used for human consumption). All this data is essential in order to carry out the simplified risk evaluation phase which is usually needed. 4 and 5. The simplified risk evaluation and the detailed risk evaluation. These are described in detail in the following section. 6. Selection of the rehabilitation strategy for a given use. This step is based on the optimization of the radiological protection. The optimization consists of a comparison of the various strategies using a number of dosimetric, economic and other criteria in order to identify the most appropriate solution. The restoration strategy depends on the intended use of the site. A change of use may make it easier to clean up the site, or may even make this unnecessary. In the majority of cases however, a number of restoration techniques will need to be applied. All applicable techniques, including soil removal, confinement in situ, and the screens, must be identified. These techniques must then be considered along with the associated storage or disposal facilities required in order to define the possible strategies. These must then be described from a number of points of view, including the reduction of the radiological impact (doses and contamination, and doses administered to the personnel cleaning the site), costs, nuisance associated with the process, lifetime of the restoration techniques, reversibility of these techniques, requirement for institutional surveillance and for maintenance of the site. The comparison of the strategies requires a summary of all the above characteristics, clearly showing the uncertainty in the evaluation. THE DECISIONAL FRAMEWORK ADOPTED The assessment work may take a long time and be very costly and the process should therefore be designed to include only those steps essential to the decision process. For example, it may become clear at the removal of doubt stage that the site is not, in fact, contaminated and the assessment may be halted at this stage. In other cases, it may be preferable to move directly from the initial diagnosis to the detailed risk assessment without carrying out a simplified risk evaluation, as this would not contribute usefully to the decisions regarding the rehabilitation of the site. Even when all the steps appear to be indispensable, the effort devoted to each should be proportional to the radiological risk and should take account of the economic, social and cultural context of the site. The risk evaluation procedure SIMPLIFIED RISK ASSESSMENT The simplified risk assessment is based on the calculation of dosimetric impact associated with the various usage scenarios for the site and its buildings, as determined by the results of the radioactivity measurements carried out on the soil and in the buildings on the site. In order to make the calculation easier, a number of generic scenarios (homes, primary school, offices, market gardening and car park) have been developed and evaluated using a calculation model providing the effective individual dose (in msv/year) associated with a given soil contamination expressed as the activity per unit mass (1 Bq/g of soil) 1 for the radionuclides likely to be found on the contaminated sites. These generic scenarios are based on simple assumptions tending to maximize the dosimetric impact in order to represent a worst case. Generic scenarios Buildings Two scenarios are considered: - buildings in commercial use. The reference group consists of the persons working in the building. - buildings in private use. The reference group consists of a parent at home and a five-year-old child. Soil A number of scenarios are considered: - home and childrens play area. A family spending most of their time in a detached house with a garden and vegetable plot located on the contaminated site. The members of the reference group whose behavior constitutes the worst case from the 176 INSTITUT DE RADIOPROTECTION ET DE SÛRETÉ NUCLÉAIRE

3 5 radiological exposure point of view are the parent at home and, more particularly, the fiveyear-old child. Over a period of a year, the child is assumed to spend 800 hours in the garden and 6,300 hours inside the house. It is also assumed that half the vegetables consumed by the child come from the vegetable plot. - offices. The workforce is assumed to be employed on a regular basis in a service industry operating in offices built on the contaminated soil. Over a period of a year, the members of the reference group are assumed to spend 20 hours in the grounds or car park and 2,000 hours inside the offices. - market garden. It is assumed that all or part of the site is cultivated by a market gardener for the production of vegetables, mainly salads, cabbages, carrots and tomatoes. Over a period of a year, the market gardener is exposed for a total of 2,000 hours by the inhalation of contaminated dust in suspension in the air during cultivation work, and by external irradiation from the soil being cultivated. The market gardener is also exposed by the ingestion of contaminated vegetables produced on the site. It is assumed that all the vegetables consumed are produced on the site. However, it is also assumed that the market gardener does not actually live on the site. - primary school. A primary school catering for children between 5 and 10 years of age is built on the site. The school consists of a number of separate buildings (classrooms, dining hall, etc.) and a playground with a compacted clay surface. The children attending the school are the most sensitive group. Over a period of a year, they are assumed to spend 350 hours in the playground and 1,230 hours inside the buildings. - free public car park. The contaminated site, of limited size, is developed as an open-air, unmanned public car park. The members of the reference group are the drivers who park their cars in the car park. Over a period of a year, they are assumed to be exposed for a total of 200 hours by external irradiation from the soil attenuated by the car park surface made up of a 10 cm layer of gravel covered with 5 cm of concrete or similar material, and by inhalation of dust arising from the landscaped areas. Two additional scenarios are also considered in order to evaluate the radiological impact associated with two other situations: Former radium site. - incursions on wasteland. The site is left under surveillance, preventing any development such as the construction of houses. However, children may break into the site in order to play. The reference group consists of children 10 years of age. - building site. The site is in the course of being developed. Two possible cases are considered, depending on whether a car park or building is under construction. In both cases, the reference group consists of the workers on the building site. Calculation of doses The doses are calculated on the basis of measurements of the radioactivity in the soil and the buildings on the site taken during the preceding stages. Following earlier treatment, the remaining contamination in the buildings is limited to the surfaces of the walls and fittings. The associated measurements relate to the dose and activity per unit mass of the contaminated walls. In the case of the soil, the concentrations used are the highest activities per unit mass, bearing in mind that the maximum values may be found at some depth due to migration rather than at the surface. The results are given for each usage scenario in terms of the annual dose (in msv/year) per unit activity in the ground together with the associated dose rate (µsv/h). The inverse values, the activities per unit mass for each usage corresponding to a unit dose of 1 msv/year, are also given. The final stage in the simplified risk assessment consists of a comparison of the calculated doses with an effective individual dose known as the selection level. Protection and environmental synergies 177

4 Figure 1 Possible decisions at the conclusion of the simplified risk assessment of the soil. Figure 2 Possible decisions at the conclusion of the detailed risk assessment. The selection level is set by the authority This selection level is expressed in msv/year and its value will be set by the government in the light of experience (to give some idea, this value should be of the order of a fraction of a msv/year). The use of a selection level enables the subsequent stages, including the detailed risk assessment and the study of restoration techniques, their cost and their effectiveness, to be omitted in certain cases when the data that they would provide would not add significantly to the knowledge on which choices were made at the simplified risk assessment stage. Assisting the choice of rehabilitation strategy The simplified risk assessment is intended to provide an initial evaluation of the radiological impact of the contaminated site in the light of the various uses to which it may be put (continuing the current usage or choice of future usage). The simplified risk assessment may be used to classify the site as one of two types (figure 1): sites which may be re-used in non-sensitive applications (as a car park, for example) without the necessity of cleaning up the site. This is normally the case when the doses associated with the measured contamination on the site and in its buildings are below the selection level. A restriction on any future change of use may be imposed. Regular monitoring of any changes in the contamination of the site and its surroundings may be required. The authorities may decide to reduce the doses if restoration methods are available at an economically acceptable cost. sites where the dose D in the reference group exceeds the selection level for the proposed usage, or where the dose D does not necessarily exceed the selection level, but where the proposed usage is considered to be more sensitive. In these situations, a detailed risk assessment should be carried out before arriving at any decision concerning the site. In the case of small sites, the topsoil may be removed completely if this will reduce the doses well below the selection level, and if such a procedure can be carried out without posing serious administrative and financial difficulties. After the site has been cleaned, it may be used without restriction. DETAILED RISK ASSESSMENT (DRA) This stage relates to the soil only, as any cleanup of the buildings will have been carried out during the preceding steps (figure 2). This stage consists initially of a detailed sampling of the site, making in-depth use of the mapping that was deliberately simplified during the initial diagnosis stage. The detailed risk is therefore based on the identification of the hydrological and geological characteristics of the site and its surroundings. The usage scenario to be considered must be specified, with a full site survey if necessary in order to choose the most realistic model for the future 178 INSTITUT DE RADIOPROTECTION ET DE SÛRETÉ NUCLÉAIRE

5 5 use of the site. The radiological impact is assessed by means of a number of indicators depending on the specific situation under consideration: the individual dose received by members of the reference group (the most exposed) and the relevant effective dose. the mean dose on the site and the relevant effective dose. the mean dose in the contaminated areas around the site and the relevant effective dose. the activity per unit mass in the ground, consumable agricultural and forestry production, meat production, milk, etc. Assisting the decision The detailed risk assessment is used to refine the initial assumptions and to choose data that is realistic in terms of the proposed usage of the site. It may therefore contribute to a reduction in the margins adopted during the simplified risk assessment and may often lead the authorities to conclude, in the case of a non-sensitive usage, that the site may be used without rehabilitation, subject to a restriction on future change of use and periodic monitoring of any changes in the contamination of the site and its surroundings. If this is not the case, an additional stage will be needed to choose an appropriate rehabilitation strategy. Management of sites and the involvement of stakeholders In simple cases small sites that can be restored without posing significant administrative and financial difficulties - the management of the site depends primarily on the resources of the technical survey. This consists of an assessment of the doses and the contamination of the soil and buildings, followed by the selection of a suitable restoration technique capable of reducing the radiological impact at an acceptable economic cost. However, in some cases, the management of contaminated sites is altogether more complex, mainly because of the large extent of the site, making any restoration difficult and costly. The management of these complex sites is governed by many considerations, among which the radiological risk, though considerable, may not play a central role. The solution preferred by the stakeholders is then the result of a compromise taking account of a number of factors dependent on the specific context of the site. However, these factors cannot be taken into account in a credible manner without the involvement of the authorities in an appropriate joint process. Whether or not choice of a suitable rehabilitation strategy is accompanied by a discussion on the future usage of the site, it should be made in the light of close cooperation between all the parties involved. The extent of this cooperation obviously depends on the context of the site, but its aim should be to review and discuss a number of possible strategies in order to arrive at a compromise that seems reasonable to all the stakeholders. The outcome of this consultation process should be the selection of a strategy corresponding as closely as possible to the following characteristics: the strategy should provide a level of health protection that is considered acceptable by both the population directly affected and the authorities; the strategy and agreed usage of the site should take account of the preferences of the local population in relation to economic and social development, and should take account of the specific cultural characteristics of the community concerned; the strategy should be compatible with the efficient allocation of the financial public resources of the country when these are deployed (as in the case of orphan sites, for example); any constraints and restrictions imposed on the strategy and agreed usage should be acceptable to the local population in the light of their future aspirations; any inconvenience caused during the implementation of the strategy should be acceptable to the affected population. Protection and environmental synergies 179