When decommissioning nuclear installations, large quantities of metal components are produced as well as significant amounts of other radioactive materials, which mostly show low surface contamination. Having been used or having been brought for a while in a controlled area marks them as ‘suspected material’. In view of the very high costs for radioactive waste processing and disposal, alternatives have been considered, and much effort has gone to recycling through decontamination, melting and unconditional release of metals. In a broader context, recycling of materials can considered to be a first order ecological priority in order to limit the quantities of radioactive wastes for final disposal and to reduce the technical and economic problems involved with the management of radioactive wastes. It will help as well to make economic use of primary material and to conserve natural resources of basic material for future generations. In a demonstration programme, Belgoprocess has shown that it is economically interesting to decontaminate metal components to unconditional release levels using dry abrasive blasting techniques, the unit cost for decontamination being only 30% of the global cost for radioactive waste treatment, conditioning, storage and disposal. As a result, an industrial dry abrasive blasting unit was installed in the Belgoprocess central decontamination infrastructure. At the end of December 2006, more than 1,128 Mg of contaminated metal has been treated as well as 313 Mg of concrete blocks. The paper gives an overview of the experience relating to the decontamination of metal material and concrete blocks at the decommissioning of the Eurochemic reprocessing plant in Dessel, Belgium as well from the decontamination of concrete containers by abrasive blasting.
Belgoprocess started the industrial decommissioning of the main process building of the former EUROCHEMIC reprocessing plant in 1990, after completion of a pilot project in which two buildings were emptied and decontaminated to background levels. The remaining structures were demolished and the concrete debris was disposed of as industrial waste and green field conditions restored. The Eurochemic reprocessing plant operated from 1966 to 1974 to process fuel from power reactors and research reactors. The main building is a large concrete structure, comprising a surface area of 55,000 m2, concrete volume 12,500 m3, and 1,500 Mg of metal components. The building is divided into multiple cells. About 106 individual cell structures have to be dismantled, involving the removal and decontamination of equipment from each cell, the decontamination of the cell walls, ceilings and floors, the dismantling of the ventilation system. Most of the work involves hands-on operations under protective clothing tailored to each specific task. Tool automation and automatic positioning systems are successfully applied. In view of the final demolition of the main process building, the main process building is divided into three parts — each part is isolated from the others. In the middle of 2008, after the removal of the NDA-IPAN/GEA installation, the eastern part will be demolished. The paper presents a status overview of the decommissioning and decontamination activities at the main process building of the former Eurochemic reprocessing plant on the nuclear site of Dessel in Belgium. The specific BELGOPROCESS approach will be highlighted, in which the decommissioning activities are carried out on an industrial scale with special emphasis on cost minimisation, the use of technology on an industrial representative scale and the specific alpha contamination of equipment and building surfaces, requiring that the decommissioning work is done with adequate protective clothing. Also specific breathing and cooling air systems have been provided to allow the operators to carry out the decommissioning tasks in acceptable working conditions.
Belgoprocess started the industrial decommissioning of the main process building of the former Eurochemic reprocessing plant in 1990, after completion of a pilot project. Two small storage buildings for final products from reprocessing were dismantled to verify the assumptions made in a previous paper study on decommissioning, to demonstrate and develop dismantling techniques and to train personnel. Both buildings were emptied and decontaminated to background levels. They were demolished and the remaining concrete debris was disposed of as industrial waste and green field conditions restored. Currently, the decommissioning operations carried out at the main building have made substantial progress. They are executed on an industrial scale. In view of the final demolition of the building, foreseen to start in the middle of 2008, a clearance methodology for the concrete from the cells into the Eurochemic building has been developed. It considers at least one complete measurement of all concrete structures and the removal of all detected residual radionuclides. This monitoring sequence is followed by a controlled demolition of the concrete structures and crushing of the resulting concrete parts to smaller particles. During the crushing operations, metal parts are separated from the concrete and representative concrete samples are taken. The frequency of sampling meets the prevailing standards. In a further step, the concrete samples are milled, homogenised, and a smaller fraction is sent to the laboratory for analyses. The paper describes the developed concrete crushing and sampling methodology.
Starting in 2003, Belgoprocess will proceed with the treatment and conditioning of some 200 m3 of widely varying high- and medium-level waste from earlier research and development work, to meet standard acceptance criteria for later disposal. The gross volume of primary and secondary packages amounts to 2,600 m3. The waste has been kept in decay storage for up to 30 years. The project was started in 1997. Operation of the various processing facilities will take 7–8 years. The overall volume of conditioned waste will be of the order of 800 m3. All conditioned waste will be stored in appropriate storage facilities onsite. In November 2002, a new processing facility has been constructed, the functional tests of the equipment have been performed and the start-up phase has been started. Several cells of the Pamela vitrification facility onsite will be adapted for the treatment of high-level and highly α-contaminated waste; low-level β/γ waste will be treated in the existing facility for super compaction and conditioning by embedding into cement (CILVA). The bulk of these waste, of which 95% are solids, the remainder consisting of mainly solidified liquids, have been produced between 1967 and 1988. They originate from various research programmes and reactor operation at the Belgian nuclear energy research centre SCK-CEN, isotope production, decontamination and dismantling operations. The waste is stored in 4800 primary packages, of which 700 contain 120 g (5.1012 Bq) radium. Half the radium inventory is present in 25 containers. The presence of radium in waste packages, resulting in the emission of radon gas, requires particular measurements. The total activity at the moment of production amounted to 18,811 TBq β/γ and 34.4 TBq α, with individual packages emitting up to 555 TBq β/γ and 2.2 TBq α. According to calculations, the β/γ activity has decreased to some 2,000 TBq, with individual packages up to 112 TBq. The extreme diversity of the waste is not only expressed in their radiological characteristics, but also in their chemical composition, physical state, the nature and condition of the packages. Radioactivity ranges between 0.01 mCi to 1,000 Ci per package. Some packages contain resins, Na, NaK and Al containing waste, poison rods, residues of fuel elements. Although most of the liquid waste are solidified, a small fraction — both aqueous and organic — still remains liquid. Primary packages may be plastic bags, metal boxes, wire gauze, La Cale`ne boxes; secondary packages may be steel drums and concrete containers. Solid waste may be sources, counters, nuclear fuel residues, filters, synthetic materials, metals, resins, granulates, rock, sludges, cables, glass, etc. Some 1000 primary packages are stored in a dry storage vault comprising 20 concrete cells, while 3800 primary packages are stored in some 2,000 concrete containers, on a concrete floor, surrounded by an earth bank to the height of the waste stacking and covered by a metal construction. At present, the annual production of similar waste amounts to 2 m3 divided over some 30 containers. Generally, the primary waste packages will be loaded in 80-1 drums (an average of 2 packages per drum), and compacted in a 150 ton hydraulic press. The pellets will be collected in 100 1 drums (an average of 3 pellets per drum). Low-level β/γ waste is transferred to the CILVA facility for further treatment, while the other 100-1 drums are filled up with sand and, in the case of radium-contaminated waste, tight-welded. Subsequently, the 100-1 drums are loaded into 400-1 drums and embedded into cement. Certain packages, for example solidified radium-contaminated liquids in welded metal containers, are conditioned as such in overpacks. Specific procedures will be established for the various non-standard waste, such as sources, control and poison rods, resins and filters, fuel residues. Highly active and/or heavily α-contaminated waste are transferred to the existing Pamela facility for treatment and conditioning. Ideally, gamma spectrometry measurements are carried out on the primary packages, but due to the extreme diversity of these packages, ranging from plastic bags containing cardboard to highly active steel valves, preference was given to measurements on the conditioned waste, or at least on already pre-compacted waste in the case of treatment in the 2,000 ton press of the CILVA facility. Thus tremendous problems of calibration can be largely avoided. All operations are remotely controlled. Transfers between buildings are carried out within appropriately shielded containers and secondary waste will be treated in existing facilities onsite. The new processing facility is being built partly over the dry storage vaults, in the immediate vicinity of the already covered storage area.
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