Guy E.R. Collard
SCK•CEN, Mol, Belgium
Tel.:+32-14-33 34 32
e-mail: gcollard@sckcen.be

Belgium has always played an important role in developing nuclear energy, in Europe and across the world. Since 1991, SCK•CEN (the Belgian Nuclear Research Centre) has focused its core competencies on three main areas : waste management; reactor safety; and public health.

Sometimes, RD&D (Research Development & Demonstration) programs deal with two or three areas. It is the case for decommissioning and remediation of contaminated sites. The RD&D Waste and Disposal research unit at SCK•CEN aims mainly at investigating the feasibility of safely disposing conditioned high-level radioactive waste in the Boom clay layer, at 225 meters below ground level at the Mol-Dessel site. It covers all aspects of the problem, from the quality of the waste packages to the safety assessment of the proposed disposal, including the experimental measurement of the migration of radionuclides in the hosting clay, in-situ experiments in the underground laboratory, technological demonstration, etc...

The Site Restoration research unit enjoys a pioneering statute with the dismantling of its BR3 (Belgian Reactor 3) reactor, the first pressurized-water reactor (PWR) built outside the USA, and now a pilot dismantling project of the European Commission. The SCK•CEN's activities also focus on reducing the waste produced by decommissioning and on restoring former nuclear sites.

This paper presents the RD&D activities performed by SCK•CEN in these fields.

Since radioactive waste and radioactively contaminated infrastructures and settlements already exist in Belgium, as a result of past and current nuclear activities, our generation has to manage them to keep potential future impact at a level that is acceptable both ethically and in terms of safety. The SCK•CEN studies and develops strategies, techniques, and technologies to achieve intrageneration equity.

In the field of nuclear waste disposal, SCK•CEN studies the interaction of radioactive and toxic waste with the underground disposal environment and also uses the results of these studies to propose both more adequate conditioning techniques for this waste and better disposal concepts. Migration tests are carried out to study the diffusion of actinides, fission products, and non-retarded species in clay, and the mobility of the dissolved organic matter in the interstitial clay water. The values of the model parameters for the migration of radionuclides and gases generated in the repository are determined by these experiments.

The SCK•CEN experimentally assesses, in parallel with modeling works, the long-term performance of various waste forms with regard to geological disposal in clay. The project focuses on waste forms of particular relevance to Belgium, e.g., high-level waste (HLW) glass and medium-level waste (MLW) bitumen (as produced by Belgoprocess and Cogéma), cemented waste, cellulose-containing waste, and spent fuel. To allow new in-situ experiments and demonstrations at full scale , the existing 67 meter long underground laboratory is being extended by a new 80 meter long gallery.

Concerning the decommissioning of nuclear installations, the SCK•CEN compared different decommissioning strategies and demonstrated that the immediate decommissioning of the SCK•CEN BR3 reactor was the most ethical and acceptable alternative. The reactor vessel will be dismantled in 1998-99 however, the reactor was stopped in 1987. SCK•CEN also develops decontamination techniques to reduce the amount of radioactive waste produced by the decommissioning of nuclear installations and to deliver a concentrated fraction of radioactive materials that can be conditioned in the most adequate manner. RD&D related to waste management and to decommissioning are performed in close collaboration with NIRAS/ONDRAF the Belgian Federal Agency responsible for the management of Belgian radioactive waste.

Concerning the management of contaminated areas, the SCK•CEN evaluates, by means of laboratory and field experiments, the mechanisms and dynamics (fluxes) of radionuclide transfers in the biosphere, considering all circumstances affecting the transfer parameters and their variability. SCK•CEN suggests the most appropriate countermeasures to reduce the transfer of radionuclides through the human and animal food chain and tests experimentally the feasibility and effectiveness of these countermeasures. SCK•CEN provides the national and international authorities with adequate information, enabling reliable assessments of the consequences for populations of routine and potential accidental releases, and the most adequate choice of mitigating actions. SCK•CEN also tries to educate professionals, students, and the public on the different aspects of radioecology, through lectures, conferences, and pamphlets.

In all these fields of activity, SCK•CEN develops and implements the As Low As Reasonably Achievable (ALARA) principle and methodologies for radiological optimization techniques in a decision-aiding framework. SCK•CEN also develops and optimizes models for evaluating the impact assessment of radioactive contamination or releases of radioactive substances in the environment, as well as existing currently contaminated sites and areas and future repository of waste.

Because SCK•CEN's responsibility toward the safety of present and future generations regarding existing waste and radioactive-contaminated settlements and environments and their negative influence on the acceptance of nuclear energy is not geographically limited, SCK•CEN participates in international organizations and programs dealing with these problems.

Based on a total installed nuclear power of 5.5 GWe and a 40 year operational period for Belgian nuclear power plants, the volume of waste of low-, medium- and high-level activity to be produced is estimated at 150.000 m³, 25.000 m³ and 5000 m³ respectively. These volumes do not include decommissioning waste.

In Belgium, the two following types of waste are considered for underground disposal:

• alpha-contaminated waste (concrete or bitumen matrix) containing significant quantities of medium-lived radionuclides (half-life exceeding 30 years), resulting from specific fuel cycle operations, mainly during spent fuel reprocessing or fuel assembly manufacturing and does not generate heat.
• vitrified heat-emitting waste (glass matrix) containing a mixture of short- or medium-lived nuclides in high concentrations, and long-lived radionuclides that are usually alpha emitters. Mainly produced during spent fuel reprocessing, it generates significant heat, owing to the fission products content.

Because of the prevailing Belgian geology, deep geological disposal in clay is the primary choice for disposal of long-lived radioactive waste. It is assumed in the present reference scenario that the operation of a repository for underground waste disposal could start in 2035 and last,until 2070/2080 (closure phase). For vitrified waste this scenario corresponds to a temporary surface storage of about 50 years, allowing the heat output to be significantly reduced.

Safe disposal of radioactive waste is one of the key issues for the global safety and the acceptability of the nuclear industry. In particular, disposal of long-lived radioactive waste, specifically spent fuel and vitrified high-level radioactive wastes are important. Disposal in deep geological formations is at present the most promising option. The understanding of the phenomena and processes in and around a deep geological repository, and of the possible transfer of radioactive substances into the biosphere is a prerequisite for evaluating the efficiency of the multi-barrier concept and the safety of the disposal system as a whole.

The mission of the Waste Disposal Research Unit is to propose, develop,and assess solutions for the acceptance and safe isolation of radioactive waste This mission supposes the following objectives:

• to provide data on characteristics of the waste and the geological environment;
• to describe, interpret, and model the characteristics of the geosphere as well as the various phenomena which control the release and the movement of radionuclides from the repository into the biosphere;
• to demonstrate the feasibility of disposal concepts, i.e., in underground laboratories; and
• to develop a consensus on methods for safety evaluations.

The verification and validation of long-term predictive assessment models of the geological environment of repositories are an essential part of this work.

For deep geological disposal, phenomena relevant to repository performance are subdivided into those occurring in the near-field and those in the far-field (geosphere). Near-field, generally considers the excavated repository or structures (including the waste packages and engineered barriers) and those parts of the surrounding rock whose characteristics have been or could be altered by the repository (excavation, temperature, radiation). The multi-barrier concept is based on the design and performance of these components.

Most research performed at SCK•CEN is carried out under contracts on behalf of NIRAS/ONDRAF and through contracts with the European Commission (EC). However, both the extent of international partnerships and the broadening of collaborations with universities complement the contractual work with exploratory and more basic studies initiated at SCK•CEN.

The SCK•CEN initiated the Belgian waste disposal program in the early 70's. Clay is the potential host rock for geological disposal. The existence of the Boom clay formation under the Mol-Dessel nuclear site and its favorable properties led to select it as a reference for the Belgian RD&D program. Research covers basic phenomena, demonstration, and conceptual studies. At present, SCK•CEN owns the only underground laboratory for the study of disposal of radioactive waste in a deep clay formation, the Underground Research Facility (URF)

Since the Belgian RD&D program has been extensively described at the WM'97 symposium ^[1], this paper lists only the objectives and the main activities of the main R&DD topics the SCK•CEN is dealing with today.

The safety of a repository for radioactive waste is determined by the long-term behavior of the engineered and natural barriers. Research on the basic phenomena expected to take place in the disposal system are therefore essential in addition to the technical demonstration tests.

The objectives of the SCK•CEN are to better understand the phenomena which control the release of radionuclides from the waste packages and their migration through the various subsequent barriers up to the environment, to model these phenomena, and to validate the related models.

Some of the research on basic phenomena listed below are carried out in surface laboratories, others in the URF ^[2].

The main objective of this research is the characterization of the waste forms, matrices and packages (cement, spent fuel, glasses, bitumen) to be disposed of in deep repositories in clay, and the evaluation of their behaviour after disposal ^{[3, 4, 5]}.

The research focus mainly on the characterization of glass, cement and bitumen matrices as barrier materials, of cement as containment material and of candidates container materials.

The main objective of this project is to improve the development, application and standardization of quality checking for waste packages, to identify R&D requirements and to coordinate the development of new test methods.

This task is carried out in an international framework. Various waste forms are considered and the SCK•CEN participates in round robin tests for various checking methods.

The main objectives of this projects are: to collect information and data from specific laboratory and field experiments as well as observations of natural geomechanical and geochemical discontinuities and to understand and to model coupled processes of the thermo-hydro-mechanical and geochemical behavior of the buffer material and the near field host rock and their interface ^{[6, 7, 8]}.

Main activities are the geotechnical monitoring of the repository and the development of conceptual models. The models are submitted to Benchmark exercises.

Because the accumulation of large amounts of gas could disturb clay layers, studying and modelling the gas generation and its transport properties from waste packages through the Boom clay are important objectives. ^[9]

The topics covered by this research are: theoretical and experimental studies of gas generation and transport, verification and validation of conceptual and numerical models of gas generation and transport and verification of the integrity of the clay barrier after gas breakthrough.

The retention of radionuclides by the host rock is a key factor of the safety of a repository. Therefore, one main objective of the R&D is to obtain and validate reliable models and data for the calculation of the migration of radionuclides through the Boom clay ^[10] .

The topics covered by this activity are: complexation with natural organics, transport and retardation processes and geochemical modeling

The HADES underground research facility is presently the only underground laboratory construction in a clay layer. The facility offers important opportunities for participation of foreign organizations and allows the SCK•CEN to be the scientific leader for waste disposal in clay layers ^[11].

The underground laboratory is mainly used to investigate and demonstrate the feasibility of disposal concepts for vitrified high-level radioactive waste, long-lived radioactive waste and spent fuel and to provide reliable data on the performance of repository barrier components.

The research carried out in the underground laboratory is related to scientific and technical aspects which are typical for clay and includes: Testing and demonstration of disposal concepts ^[12], backfilling and sealing of repository ^[13], long term behavior of repository components, ground water flow analysis and radionuclide migration ^{[14, 15]}, monitoring of reconsolidation of the disturbed zone of the Boom clay ^[16].

The development an acceptable approach and methodology for evaluating the long-term safety of radioactive waste disposal in clay is one of the main objectives of the project. Radiological and non-radiological (chemical-toxic) consequences have to be evaluated ^{[17, 18, 19]}.

The activities in the field of the safety of waste disposal comprise: Assessment of the disposal of reprocessed waste, preliminary assessment of the disposal of spent fuel, evaluation of the non-radiological consequences, comparison with natural analogues; development of approaches taking into account climate changes and human intrusion and contribution at international level to the information of the public with a view in the public acceptance of nuclear waste disposal systems.

We are mainly considering the disposal of long-lived MLW, heat producing vitrified HLW and spent fuel (SF). As mentioned above, the disposal of radioactive waste in stable, deep geological formations is, therefore, a very attractive concept. To ensure the isolation of the radioactive waste from the biosphere for a very long time and to prevent easy access to the waste, a series of guidelines have been established. Only geological formations stable since several millions of years and for which stability is expected in the future are considered. We further propose a deep underground location for the repository in a formation with sufficient thickness. The formation considered must of course allow the construction of a repository and have promising properties for the isolation of the waste for sufficiently long time periods^[20]. The concept is rather independant of expectable changes of of fuel cycle or of fuel and waste management options, e.g. the application of "Partitioning and Transmutation" operations into the reprocessing process ^{[21, 22]}.

Since 1978, different repository concepts have been considered for the disposal of high-level and long-lived radioactive waste in the Boom clay layer at the Mol-Dessel site. The concept now considered by NIRAS/ONDRAF is based on a separation of the heat producing high-level radioactive waste and the long-lived medium level radioactive waste. Approximate dimensions (expressed in diameter) for the different components are 6m for the shafts, 4m for the primary galleries, 3.5m for the MLW disposal galleries, and 2m for the HLW disposal galleries. The length of the disposal galleries would be 800m and the distance between shafts about 400m. Mainly concrete would be used to line both shaft and galleries. The linings will be designed to ensure mechanical stability during the operational phase of the repository. According to the respective disposal concepts hereafter mentioned, we need a comparable length of galleries for the disposal of both waste categories. ^[23]

For the non-heat producing long-lived MLW, the canisters will be disposed in separate galleries. The whole section of the galleries will be filled with MLW canisters and the remaining voids will be backfilled, possibly with concrete. Few research has been done for this concept up to now.

The concept for the HLW disposal galleries has been studied much more in detail. The HLW canisters are assumed to be placed in long thin metallic tubes in the centre of the disposal galleries. These tubes are designed to remain intact during the thermal transient of the heat producing waste. Pre-compacted calcium bentonite blocks are considered for the filling of the void between the metallic tube and the concrete gallery lining

The sound management of nuclear facilities includes the existence and maintenance of a decommissioning plan for these infrastructures. This document involves the description of the legal framework, the safety, technical and environmental principles of the decommissioning as well as the evaluation of the decommissioning costs. According to the legal rules, an initial decommissioning plan has to be drawn up by the licensees of new nuclear facilities. Revisions are requested every five years and the final decommissioning plan must be available at least three years before the final shutdown.

In 1995, SCK•CEN has submitted the initial decommissioning plan to the Belgian Authorities covering all its nuclear facilities: the BR1 research reactor, the BR2 materials testing reactor, the VENUS zero-power reactor, the laboratories wherein the fabrication of MOX fuel has been developed, and several other laboratory complexes^[24]. Moreover, the SCK•CEN wrote down the final decommissioning plan of BR3, the first PWR (Pressurized Water Reactor) installed in Western Europe^[25].

The SCK•CEN has designed a multi-entry model computing the decommissioning costs. This model uses an interactive database covering all aspects of the physical and radiological inventory, available decommissioning and dismantling techniques, operational "unit costs" deduced from own experience and external projects, costs of further management of waste.... The model allows simulation of different decommissioning strategies, with a special attention to the waste produced and the costs of the operations.

The SCK•CEN has decommissioned three laboratory complexes: the former Physics building; the Metallurgy building; and Block 3 of the Chemistry building. In the past, uranium, thorium, cesium, strontium, americium, etc. have been handled or used in these laboratories. Decommissioning attests and acceptance statements were obtained respectively from the Safety Service of the SCK•CEN and the one of the present owner of the buildings. The laboratories have indeed been transferred for non-restricted use to a non-nuclear research institute.

SCK•CEN has demonstrated that it has decommissioning and measurement techniques available to clear, according to the legal rules, old laboratories to the level of unrestricted re-use in such a way that they can be accepted by the non-nuclear world. ^[26]

Other buildings are still affected by decommissioning activities. Here, the purpose is to dismantle the aged equipment to make room for new nuclear R&D projects. The activities so far are mainly focusing on the dismantling of glove boxes and hot cells.

The BR3 reactor started in 1962 and definitely shut-down in 1987, after almost 86000 EFPH. In 1989, the BR3 was selected as one of the four pilot decommissioning projects by the EC in the framework of its five-year program for the decommissioning of nuclear installations. An "ALARA" approach, specific for dismantling operations, has been developed with the decommissioning of BR3 as test and demonstration case ^[27]. The main important aspects of the project are described in detail in an other paper ^[28].

The main issues are ^{[29 - 33]}:

• The pre-dismantling chemical decontamination of the primary loop is effective in saving doses and costs. Moreover, it leads to the decategorization of an important fraction of the waste originated by the reactor internals.
• The most important parameters influencing the choice of remote dismantling techniques are the production of the secondary waste and the dose uptake by workers. Moreover, for the underwater cutting strategy applied, it appeared that the cutting time itself covers only a small fraction of the total operational time therefore, the cutting speed is not the major parameter when estimating the costs and the dose uptake of a dismantling operation.
• Deferring the dismantling by 30 years does not significantly reduce dose uptakes to workers. The SCK•CEN was able to compare in-situ the direct dismantling with the 30 years deferred dismantling of highly active pieces. Indeed, the BR3 disposed of two sets of irradiated internals, one of which having been unloaded 30 years ago, and being stored in the plant during this period. The actual dismantling of both sets of internals showed that no real reductions for dose and waste can be expected from such a deferring period.
• An important fraction of the contaminated equipment and infrastructure can be fully decontaminated and "free released". For the treatment and management of waste generated by the dismantling of contaminated material, the main preferred option is to free release and recycle as much material as possible ^[34]. Therefore, a thorough decontamination workshop is installed to handle the waste stream coming from the dismantling of loops and contaminated equipment.

• Because research institutes as the SCK•CEN generates special wastes, specific RD&D programs are needed to solve these particular problems. Ongoing RD&D projects at the SCK•CEN include, among others:The conditioning of activated aluminum (originated by the BR2 reactor), the conditioning of aluminum raises the question of its compatibility with concrete;
• The recycling of chemical solutions used for decontamination of metals, the regeneration of Ce4+ to minimize the secondary waste produced by a semi-industrial decontamination unit ^[35];
• Treatment of contaminated sodium (originated by LMFBR programs),: a dedicated immobilization technique is being developed;
• Optimization of concrete dismantling, decontamination, and conditioning techniques to minimize the dismantling costs (concrete represents almost 20 % of the decommissioning costs);
• Modeling of activation in the power-plant infrastructure (reactor vessel and internals, concrete, ...);
• Sonochemistry applied to decontamination techniques; and
• Selective extraction of cobalt by means of immobilized ligands.

Site and environmental restoration issues are well known to SCK•CEN, which masters the tools and the methodology both for assessment and remediation. Our models and corresponding computer codes allow real-time assessments of accidental releases of radioactivity, assessments of the impact of former nuclear sites, probabilistic consequence assessments, and radiological protection. Furthermore, our measurement facilities have proved their performance on many occasions. In nuclear spectrometry, for example, we analyze thousands of samples each year. We are also well equipped for low-level measurements of environmental and biological samples. Finally, to remedy soil contamination problems, the SCK•CEN performs research in radioecology in our experimental farm: we study the mechanisms of plant and animal intake, and devise appropriate countermeasures to reduce the transfer of radionuclides through the food chain.

Projects dealing with radiological characterization of sites have been or are carried out for the federal government and for the private industry. Characterization activities include:

• Radiological characterization of the surroundings of a former Radium production plant;
• Radiological characterization of waste dumps of a Phosphate production plant;
• Radiological characterization of the Belgian territory after the Chernobyl accident ^[36];
• Radiological survey program of the Belgian territory; and
• Monitoring and clean-up of roads on a power plant site.

SCK•CEN developed the characterization strategy for these projects and developed or adapted the necessary instrumentation for the specific needs of each project.

Non-radiological characterization of sites is an important part of projects dealing with the safe disposal of waste and site remediation. The SCK•CEN performed the geological and hydrological characterization of the region around the underground laboratory. The underground has been fully characterized in order to estimate or determine the migration of radionuclide from the underground facility into the biosphere. The studies include the mechanical, geological, hydro-geological, and chemical, and other characterizations of the site.

The SCK•CEN participated in a study carried out on behalf of EC-Direction Générale XI ( to identify the important "non nuclear" parameters and site characteristics to be considered in the radiological assessment procedures for site restoration. .

In the RESTRAT project (REstoration STRATegies for radioactive-contaminated sites and their close surroundings), a new project in the new EC four-year programme, working packages are devoted to the characterization of example sites (Drigg repository, Neet-river, Ravenglass estuary, Ranstad) and the dependence of important physico-chemical parameters (mainly sorption coefficient (K_d)) on the composition and state (e.g., pH) of liquid and solid phases.

Since 1982, SCK•CEN has been performing safety assessments for the waste repository in the Boom clay layer situated under its own Mol-Dessel site. These assessments include the definition of needed parameters, elaboration and execution of the experimental program leading to these parameters, elaboration of tests, validation and application of models allowing the mandated authorities to decide. These activities constitute an important part of the involvement of the SCK•CEN in the Belgian and European programs on geological disposal of waste.

The SCK•CEN develops methodologies for radiological optimization techniques in decision-aiding frameworks. It also participates in the implementation and the practical application of such methodologies ^{[37 - 39]}.

The SCK•CEN also participates in international and national programs dealing with site restoration, including:

• Status of the restoration of contaminated sites in Europe ^[40];
• Development of a general guideline for the radiological optimization of the restoration of former nuclear sites;
• Restoration of the environmental contamination from the former radium plant of Sint-Jozef-Olen;
• RESTRAT: development of a generic methodology for ranking restoration techniques as a function of sites characteristics.

For more than forty years, the SCK•CEN has promoted and studied major wide environmental themes that relate to remediation efforts and associated innovative technology research. The themes include radioactive and mixed waste reduction, treatment and conditioning, waste disposal, characterization and monitoring sensors, decontamination of structures, decommissioning, ecological use of contaminated sites, etc....

The SCK•CEN decontaminated four former nuclear laboratory complexes and transferred them to a non nuclear research institute for unrestricted use. In the past, uranium, thorium, caesium, strontium, americium, etc. have been handled or used in these laboratories. Decommissioning attests and acceptance statements were obtained respectively from the Safety Services of the SCK•CEN and of the new owner. They are now, after renovation work, again used for non- nuclear R&D projects.

The SCK•CEN is called by external clients when needed to supervise the decontamination of buildings.

The SCK•CEN is involved in several international collaborative programs supported by EC contracts. These programs deal with the transfer of radionuclides in agricultural ecosystems and aim ultimately to define the most effective countermeasures ^{[41 - 51]}.

The European RESSAC-EUROSOIL ("REhabilitation des Sols et des Surfaces après un ACcident") program studies the environmental consequences of an accidental release from PWR as well as the efficacy of possible remedial actions. Simulated radioactive aerosols are generated and deposited on soils and plants in lysimeters. The behavior of the radionuclides associated with the particles and their availability for plant uptake is quantified under different scenarios.

The FARM (Factors Affecting Radionuclides Metabolism) program investigates the influence of various factors, both animal-dependent (breed, age, physiological status,etc.) and animal-independent (soil-particles ingestion, nature of the feed, etc.), on the absorption and metabolism of radionuclides by ruminants. The SCK•CEN studies the mechanism of plant and animal intake, and devise appropriate counter measures to reduce the transfer of radionuclides (with a special attention to ¹³¹Iodine) through the food chain.

The EC-CHERNOBYL PROGRAM ECP-2 (Transfer of radionuclides through the terrestrial environment to agricultural products and livestock, including the evaluation of agrochemical practices) focuses on the problems caused by the radioactive contamination in the former Soviet Union and evaluates the efficiency of the best suited countermeasures. The SCK•CEN studies the environmental consequences of an accidental release from PWR as well as the efficacy of possible remedial actions. Simulated radioactive aerosols are generated and deposited on soils and plants in lysimeters; the behavior of the radionuclides associated with the particles and their availability for plant uptake is quantified under different scenarios. Agrochemical countermeasures (application of fertilizers, organic and aluminosilicates amendments, and Ammonium-Ferric-Hexacyano-Ferrate (AFCF) as a cesium-binding agent and the use of physical barriers (straw mulching) to prevent plant contamination by rain splash and soil resuspension are presently investigated. They were tested on various agricultural crop species grown at sites selected on the basis of their different soil properties and deposit characteristics. Some of these countermeasures were used in combination.

The SCK•CEN is still developing decontamination and treatment processes to separate the radioactive fraction from the bulk of radioactively contaminated materials. Chemical processes are generally used, but some of the techniques could also use biological reactants.

On going studies covers removal of traces of Pu from traces, decontamination of low level liquid wastes, detritiation of liquids, solids and sludges, destruction of organics, ....

SCK•CEN (the Belgian Nuclear Research Centre) has always played an important role in developing nuclear energy, in Europe and across the world. Since 1991, SCK•CEN has focused its core competencies according to its new mission, which includes:waste management, reactor safety, and public health. Broadly speaking, these are the three main areas along which the research divisions articulate themselves. To-day's SCK•CEN , more than ever, benefits health, safety and the environment. We contribute to the protection of the environment by tackling the radioactive waste issue and we heal the environment by helping remediate contaminated sites and environments.

1. B. NEERDAEL, G. VOLCKAERT, A. SNEYERS , "Past and Current R&D Programme for Waste Disposal in Belgium", Proc. WM'97, session 7, paper 07-08, March 2-6, 1997, Tucson, Arizona (1990).
2. BONNE, G. COLLARD, J. MARIVOET, B. NEERDAEL, P. VAN ISEGHEM, "SCK•CEN 's Integrated R&D and DT&E Programme on Final Nuclear Waste Disposal in Argillaceous Formations", Conf. Waste Management '92,Tucson, March, 1-5, 1992.
3. P. VAN ISEGHEM, K. BERGHMAN, K. LEMMENS, W. TIMMERMANS, W. LIAN, "Laboratory and In Situ Interaction between Simulated Waste Glasses and Clay", Final Report CEC contract FI1W-0100/179, 1985-1989, Ed. CEC, EUR 13607 (1992).
4. P. VAN ISEGHEM, T. AMAYE, Y. SUZUKI, H. YAMAMOTO, "The Role of Al₂O₃ in the Long-Term Corrosion Stability of Nuclear Waste Glasses", Journal of Nuclear Materials, 190, 1992, pp. 269-276, Elsevier Science Publishers B.V.
5. P. VAN ISEGHEM, K. LEMMENS, M. AERTSENS, M. PUT, "Interaction between HLW Glass and Clay: Experiments versus Model", Conf. GEOVAL'94, Paris, 11-14 October 1994.
6. L. NOYNAERT, R. BEAUFAYS, et al., "Cerberus. A Demonstration Test to Study the Near-Field Effects of an HLW Canister in an Argillaceous Formation", Activity Report 1990-92, contract FI2W-0003, ONDRAF/NIRAS, Ed. CEC, EUR 15718 EN (1994).
7. F. BERNIER, "ModJlisation du Comportement Thermo-Hydro-MJcanique de l'Argile de Boom dans le But de la Quantification des InterfJrences entre Excavations et ExpJriences Voisines", Ed. SCK$CEN, BLG 666 (1994).
8. K. HART, B. ROBINSON, T. PAYNE, P. VAN ISEGHEM, K. LEMMENS, "Interaction between Np-doped Synroc and Boom clay", Kyoto, Japan, 23-27 October 1994., Proc. Scientific Basis for Nuclear Waste Management XVIII, Mat. Res. Soc. Symp. Vol. 353 (1995).
9. G. VOLCKAERT, L. ORTIZ, M. PUT, "In-Situ Water and Gas Injection Experiments Performed in the HADES Underground Research Facility", Proc. Of the A5th International Conference on Radioactive Waste Management and Environmental Remediation@, Berlin, 3-7 September 1995, pp. 743-750, Ed. S. Slate, The American Society of Mechanical Engineers, 1995, ISBN 07918 1219 7.
10. M. PUT, J. MARIVOET, G. VOLCKAERT AND B. NEERDAEL , "How Performance Assessment of a Geological Waste Disposal in Clay has Contributed to Focus the Radionuclide Migration Research", WM'98, March 1-5, Tucson, Arizona.
11. G. COLLARD, R. ANDRE-JEHAN, A. BONNE, R. MAIR, "The HADES Project: an Underground Demonstration Facility for the Disposal of High-Level Waste in Plastic Clay", Proc. Third European Community Conf. on Radioactive Waste Management and Disposal, Luxemburg, 17-21 Sept. 1990, pp. 418-436, Ed. Elsevier applied Science, (1991), ISBN 1-85166-657-5.
12. F. BERNIER, B. NEERDAEL, "Overview of In-Situ Thermomechanical Experiments in Clay: Concept, Results and Interpretation", International Workshop on "Thermo-Mechanics of Clays and Clay-Barriers", Bergamo, 20-22 October, 1993.
13. H.R. THOMAS, A. GENS, G. VOLCKAERT, M.V. VILLAR, C. IMBERT, "Testing and Modelling the Behaviour of Unsaturated Argillaceous Backfill and Sealing Materials", 4th Conf. of the EC on "The management and disposal of radioactive waste", Luxemburg, 25 - 29 March 1996.
14. G. VOLCKAERT, "Water Drainance Through the Boom Clay: an Overview of the Research at the SCK$CEN Site at Mol", Proc. OECD/NEA-SEDE Workshop on "Waterflow through Argillaceous Media", Baden (Ch), March 15-16, 1991.
15. M. PUT, "Three Dimensional In-Situ Migration Experiment in the Boom Clay Formation at the Mol Site in Belgium", INTRAVAL Conf., Seattle, 22-26 April 1991.
16. NEERDAEL, D. DE BRUYN, G. VOLCKAERT, "Current Status and Future Plan of Research on the Rock Deformation and Disturbed Zone within the HADES-Project", International Workshop on "Research and Development of Geological Disposal", Abstracts of Technical Sessions, PNC Tokai, Japan, 15-18 November 1993.
17. WEMAERE, J. WALRAEVENS, G. VOLCKAERT, J. MARIVOET, "Evolution of the Influence of Glacial and Periglacial Effects on the Hydrological System in the Frame of a Performance Assessment of the Geological Disposal of Radioactive Waste in a Clay Layer", Poster, Workshop on "Glaciation and Hydrogeology" organized by Nordic Nuclear Safety Research (NKS), Hässelby, Sweden, 17 - 19 April 1996.
18. BONNE, "Long Term Safety and Performance Aspects of High Level Waste Disposal in Clay", Seminar on "Safe Disposal of Radioactive Waste: the Path to Achievement", Brussel, 22-23 march 1990.
19. J. MARIVOET, T. ZEEVAERT, "PACOMA: Performance assessment of the geological disposal of medium-level and alpha waste in a clay formation in Belgium", SCK$CEN BLG 629, EUR 13042 EN (1991).
20. DE BRUYN, A. FONTEYNE, J. MARIVOET, M. MONSECOUR, L. NOYNAERT, M. PUT, G. VOLCKAERT, "Near Field Concepts for Disposal of Radioactive Waste in a Clay Formation", Ed. CEC, EUR 13844 EN, 1992, ISSN 1018-5593.
21. NEERDAEL, G. COLLARD, C. DERAEDT, L. BAETSLE, P. DEJONGHE, J. MARIVOET, "Projects CAPRA et SPIN", Ed. SCK· CEN, BLG-676 (april 1995).
22. G. COLLARD, L. BAETSLE, J. MARIVOET, P. DE REGGE, C. DERAEDT, "Mogelijke Ontwikkelingen van de Splijtstofcyclus in België", Ed. SCK•CEN, BLG-675 (april 1995).
23. J. VERSTRICHT, B. NEERDAEL, L. VAN CAUTEREN, "Field Measurements for the Demonstration of the Concept for Radioactive Waste Disposal", 4th International Symposium on AField Measurements in Geomechanics@, Bergamo, Italy, 10-12 April 1995.
24. L. NOYNAERT, V. VAN ALSENOY, R. CORNELISSEN, S. HARNIE, "Decommissioning Plan of a Nuclear Research Centre: Lessons Learned by the SCK•CEN, WM'97, Tucson, 1997.
25. L. NOYNAERT, V. MASSAUT, R. CORNELISSEN, M. KLEIN, "Decommissioning Costs of the BR3 Reactor", Annual Meeting on Nuclear Technology '96, Mannheim, Germany, 21-23 May 1996, ISSN0720-9207, p543-546.
26. L. NOYNAERT, J. MARIEN, R. CORNELISSEN, S. HARNIE, "Unrestricted Reuse of Decommissioned Buildings," European Nuclear Society (ENS), Topseal'96, Stockholm, Sweden, June 9-12, 1996. ISBN 3-9520691-2-4.
27. V. MASSAUT, P. DEBOODT, F. VERMEERSCH, A. LEFÈBVRE, M. KLEIN, "Optimization and Decommissioning: Challenge and Limits", 1st European ALARA Network Workshop, December 1-3, INSTN Saclay, France.
28. Y. DEMEULEMEESTER, V. MASSAUT, M. KLEIN, A. LEFEBVRE, "The BR3-PWR Decommissioning Project : Present Status and Lessons Learned", WM'98, March 1-5, Tucson, Arizona.
29. V.MASSAUT, M. KLEIN, L. NOYNAERT, J. DADOUMONT, A. LEFÈBVRE, "The BR3 Decommissioning Project--Lessons for the Future of Nuclear Energy", European Nuclear Society (ENS) Class 1 topical meeting on Research Facilities for the Future of Nuclear Energy, Brussels, Belgium, June 4-6, 1996, Proc. 105-112.
30. V. MASSAUT, M. KLEIN, J. DADOUMONT, P. ROBERTS, A. LEFÈBVRE, "The Design, Construction and Deployment of a Large Underwater Bandsaw for Decommissioned LWR Internals Dismantling," British Nuclear Energy Society (BNES) Int. Conf. on Remote Techniques for Hazardous Environments, Leicester, United Kingdom, April 29-30, 1996.
31. V. MASSAUT, M. KLEIN, A. LEFÈBVRE, "The BR3 PWR Pilot Decommissioning Project, First PWR Decommissioning in Europe," American Nuclear Society (ANS) Topical Meeting--Best of D&D, Chicago, Illinois, USA, April 14-17, 1996.
32. V. MASSAUT, H. STEINER, H. STERNER, "Waste Minimization during Decommissioning: Practical Experience from the EU Pilot Decommissioning Projects BR3 Mol and KRB-A Gundremmingen and from the EWN Plant Decommissioning", European Nuclear Society (ENS) Topseal'96, Stockholm, Sweden, June 9-12, 1996, ISBN 3-9520691-2-4.
33. J. DADOUMONT, V. MASSAUT, M. KLEIN, "Pilot Dismantling of the BR3 Pressurized-Water Reactor", Fifth Asian Symp. on Research Reactor (ASRR-V), Taejon, Korea, May 29-31, 1996, Proc. Vol. 1-2, 652-659.
34. H. WILLE, M. KLEIN, "Assessment of Decontamination Procedures for VVER-PWR's" for Waste Minimization", Decommissioning of Nuclear Installations, Published by the EC, 389-396 (1995).
35. M. KLEIN, A. RAHIER, ``Thorough Decontamination of Metallic Pieces with the Cerium Process,'' Spectrum 1996, Seattle, Washington, USA, August 18-23, 1996.
36. J. UYTTENHOVE, S. POMMÉ, B. VAN WAEYENBERGE, F. HARDEMAN, J. BUYSSE, J.-P. CULOT, "Follow-Up of the Chernobyl Cs-137 Concentration in Belgium by Means of In Situ Gamma Spectroscopy," Annalen van de Belgische Vereniging voor Stralingsbescherming 21:4, 329-338 (1996).
37. N. PAUWELS, F. HARDEMAN, K. SOUDAN, "Assessing the Economic Impact of the Decision to Evacuate an Industrial Area. Do the Existing Models Apply?," Seminar on the Consequences of a Nuclear Accident: An Economic and Radiological Approach, Belgian Association for Radiation Protection (BVS/ABR), Brussels, Belgium, June 14, 1996.
38. N. PAUWELS, B. VAN DE WALLE, A. SOHIER, F. HARDEMAN, K. SOUDAN, "Nuclear Incident Response in Industrial Areas: Assessing the Economic Impact of the Decision to Evacuate," Third Regional Meeting on Nuclear Energy in Central Europe and Third COSYMA and Int. MACCS Users Groups Meeting, Portoroz, Slovenia, September 16-19, 1996.
39. N. PAUWELS, B. VAN DE WALLE, F. HARDEMAN, K. SOUDAN, "The Options Approach to Irreversible Decisions Affecting the Environment. The Nuclear Case, "Int. Workshop on ``How Do Economists Cope with Environmental Uncertainty and Complexity?", Fondation Universitaire Luxembourgeoise (FUL), Arlon, Belgium, October 15-17, 1996.
40. TH. ZEEVAERT, H. VANMARCKE, P. GOVAERTS, "Status of the Restoration of Contaminated Sites in Europe,'' EC DG XI Contract 94-PR-014, Final Report (September 1996).
41. H. VANDENHOVE, M. VAN HEES, S. DE BROUWER, C. M. VANDECASTEELE, "Transfer of Radiocaesium from Podzol to Ryegrass as Affected by AFCF Concentration," Sci. Tot. Environ. 187, 237-245 (1996).
42. Y. THIRY, "How Short-Rotation Forest Crops Can Be Used for Sustainable Remediation of Contaminated Areas," Topical day on Site Restoration, SCK•CEN, Mol, Belgium, September 18, 1996, BLG 721, 42-46.
43. N. LEWYCKYJ, C. M. VANDECASTEELE, A. CREMERS, "Laboratory Study of the Caesium Migration in a Podsolic Sandy Soil as a Function of the Ionic Composition of the Soil Solution", Int. Symp. on Radioecology, Vienna, Austria, April 22-24, 1996, Proc., Mitt. D. Österr. Bodenkundl. Ges. 53, 51-59 (1996).
44. VALCKE, C. M. VANDECASTEELE, M. VIDAL, A. CREMERS, "The Use of Mineral and Organic Adsorbents as Countermeasures in Contaminated Soils: A Soil Chemical Approach", Int. Symp. on Radioecology, Vienna, Austria, April 22-24, 1996, Proc., Mitt. D. Österr. Bodenkundl. Ges. 53, 85-92 (1996).
45. Y. THIRY, C. M. VANDECASTEELE, B. DELVAUX, "Ability of Specimen Vermiculitic Minerals to Fix Radiocaesium: Effect of the Chemical Environment," Int. Symp. on Radioecology, Vienna, Austria, April 22-24, 1996, Proc. Mitt. D. Österr. Bodenkundl. Ges. 53, 93-100 (1996).
46. H. VANDENHOVE, M. VAN HEES, S. DE BROUWER, C. M. VANDECASTEELE, "Effect of AFCF on the Soil-Plant Transfer of Cs-134," Int. Symp. on Radioecology, Vienna, Austria, April 22-24, 1996, Proc. Mitt. D. Österr. Bodenkundl. Ges. 53, 145-153 (1996).
47. C.M. VANDECASTEELE, P. J. COUGHTREY, R. KIRCHMANN, "Impact of the Chernobyl Accident on the Environment and Management of Contaminated Areas," Workshop on Chernobyl, Ecological and Health Impact, 10 Years of Observation, Brussels, Belgium, April 23, 1996. To be published in Annales de l'Association Belge de Radioprotection.
48. C.M. VANDECASTEELE, P. J. COUGHTREY, R. KIRCHMANN, "Impact of the Chernobyl Accident on the Environment and Management of Contaminated Areas," Seminar on Chernobyl, Ecological and Health Impact, Doel, Belgium, June 7, 1996.
49. C.M. VANDECASTEELE, E. VALCKE, M. VAN HEES, H. VANDENHOVE, Y. THIRY, "Amendments as Agricultural Countermeasures," Int. Academic Conf. on Ten Years After the Chernobyl Catastrophe, Minsk, Bielorussia, CIS, October 7-12, 1996, to be published as UNESCO document.
50. C.M. VANDECASTEELE, P. J. COUGHTREY, R. KIRCHMANN, "Environmental Consequences of the Chernobyl Accident," Int. Academic Conf. on Ten Years After the Chernobyl Catastrophe, Minsk, Bielorussia, CIS, October 7-12, 1996, to be published as UNESCO document.
51. N. LEWYCKYJ, Y. IVANOV, "Transfer of Radionuclides through the Terrestrial Environment to Agricultural Products, Including the Evaluation of Agro-Chemical Practices, Sub-Chapter C2 "Vertical Migration of Cs-137, Sr-90 and Other Radionuclides"," EC, Final Report of the Experimental Collaboration Project no. 2 (ECP-2), 95-106 (1996), EUR 16528 EN.

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