Radwaste management: L/ILW
Disposal of short-lived waste in France20 April 2012
Although France has two operating low-level waste facilities it recognizes that these are rare resources.?New waste management options are therefore being investigated for recycling of metallic wastes and disposal of large components. By Gérald Ouzounian, Michel Dutzer and Patrice Torres
France’s experience in the management of radioactive waste is supported by 40 years of operational activities in the field of surface disposal of low-and intermediate-level short-lived waste (LILSLW) and of very low level waste (VLLW). The so-called Centre de la Manche started operation in 1969, and 527,000 cubic-meters of waste packages were disposed by the end of operation in 1994. After capping works, this facility has entered its institutional control period for 300 years. In 1992, the Centre de l’Aube disposal facility took over from Centre de la Manche. Its design benefited from Centre de la Manche experience. More recently, in 2003, the Morvilliers disposal facility opened to accept very low level waste, in particular to accommodate waste generated by decommissioning activities.
French government national radioactive waste management agency ANDRA is now responsible for three disposal facilities that are at very different stages of their lives: institutional control, mature operational phase, beginning of operational phase. The feedback of the experience of one facility to the others is an important way to ensure safe and exemplary operation. It is also important for the development of new disposal routes. Furthermore there can be changes in the operational conditions of the facilities: new needs for disposal may appear, increased requirements for sustainable development, new regulations. Moreover, some of the experience gained may be beneficial for the geological repository to dispose of high-level and intermediate-level long-lived wastes in France, now in its industrial preparation phase, and due to start up by 2025 in France. Therefore ANDRA continuously adapts its industrial tools to this changing environment. This includes of course the tools to take charge of the wastes, but it also includes the capacity to adapt its ongoing operations, as well as to re-assess the situation of the closed facilities.
Centre de la Manche
Located next the La Hague facility, Centre de la Manche was commissioned in 1969 and received low and intermediate-level short-lived waste packages until June 1994.
Operations at Centre de la Manche were authorised by an order signed in 1969. Disposal started in October 1969.
Pursuant to the new nuclear legislation implemented in 1973, a first safety report was prepared in 1975. The Atomic Energy Commission (CEA), owner of the facility at that time, entrusted it in 1979 to the new ANDRA organisation created within the CEA by a cabinet order. The December 1991 waste act transformed ANDRA into an independent organization.
Waste acceptance criteria have evolved considerably during the operational lifetime of the Centre de la Manche. The order of 1969 referred to concentrations using the volume as a reference (maximum permitted concentration in drinking water, or MPC) to define the disposal modes, water being the main contamination vector. Beyond 1000 MPC (5x10-5 Ci/m3 for Pu-239) waste contained in drums and products in bulk had to be disposed of in concrete cells before being grouted with concrete. The waste could also be disposed of directly in the ground provided it was packaged, in cement blocks or in cemented drums, against any risk of water leaching. Below 1000 MPC, bulk waste could be disposed in trenches. So when operations started at the facility, there was no activity limit for the waste, except to define the packaging and disposal modes.
Therefore the first types of disposal cells were simple trenches, concrete trenches or above-ground platforms (Figure 1). Due to water infiltration problems, three simple trenches were built but only two were used and waste from one was retrieved.
The first activity limitations for waste were proposed in the 1975 safety report. The conceptual design with regard to safety for a surface disposal facility was progressively established. Finally, in 1985, basic safety rule RFS I.2 formalised the incorporation of these acceptance criteria into long-term safety objectives. It prescribed that, following a post-institutional control phase lasting no more than 300 years, the intrinsic safety of the disposal facility relies on the limitation of activity in long-lived emitters of the disposed waste, and on site properties. Thus, the average specific activity in alpha emitters of the entire set of waste packages contained in the disposal facility at the end of the institutional control period should not exceed 0.01 Ci alpha per tonne (370 MBq alpha per tonne). The maximum specific activity in alpha emitters of each waste package had to remain under 0.1 Ci alpha per tonne (3.7 GBq alpha per tonne).
As a complement, the 1986 basic safety rule RFS III.2e imposed systematic waste packaging and established minimum characteristics, particularly with regard to containment, with which packages must comply depending on the nature and activity of the waste. Containment properties of waste packages and disposal structures had to be considered until the end of the institutional control period.
ANDRA incorporated all of these requirements in its technical specifications and notified the waste generators who intended to send their waste to the agency. Moreover, an acceptance process was set up to verify, first, that waste packages satisfied ANDRA’s technical requirements, and second that waste generators had identified and implemented the prescriptions ensuring the quality of the packages generated.
The design of the disposal structures continuously improved. In particular rainwater that may have been contaminated by waste packages was separated from rainwater that fell outside disposal structures: a dedicated water collection network was gradually implemented beginning in 1979. This system includes an underground gallery for sampling and monitoring. The traceability of waste packages benefitted from the availability of computerised systems. In 1984 a fully-computerised system was implemented to follow up waste packages, from generating facilities to disposal structures.
Handling techniques remained rather rustic during the whole operational time of Centre de la Manche. Generally workers were operating very near to waste packages.
The design of the final capping system to protect the disposal facility against rainwater is multilayer, including a bituminous membrane. The choice of bitumen instead of a mineral material was motivated by the possibility of subsidence of packages in the most ancient parts of the facility. Capping works began in 1991. The approach for the institutional control period was proposed by ANDRA and the order authorizing the launch of the institutional control period was issued in 2003.
Table 1 shows the efficiency of the capping system for the reduction of volume and activity collected in the underground monitoring galleries. Most of the volume of collected water comes from local defects that are not related to the quality of the membrane.
During these first years of institutional control period, the maintenance of the memory of the facility was organized. The documentation of the facility was duplicated on long-life paper. A copy of this documentation is presently stored at the French National Archives. A summary was also prepared for local administration and municipalities. These data will be useful to review periodically the situation of the disposal facility in the future.
Centre de l’Aube
The design of the Centre de l’Aube disposal facility fully takes into account French basic safety rules that were developed during the operation of Centre de la Manche. The facility makes use of an up-to-date technology that improves radiation protection for workers.
Its site, located in the Aube district, near the village of Soulaines-Dhuys, was selected based on its very simple geology that meets safety requirements: a layer of sand above a layer of impermeable clay protecting water resources. The outlet of underground water in the layer of sand is well-identified: a small river which flows along the facility.
The facility has a capacity of 1,000,000 m3 of waste packages. Disposal structures are designed to protect waste packages from rainwater during operations. A mobile roof that includes a crane and all control equipment and instrumentation is moved once a cell has been filled and covered with a watertight coating. A separative water collection system collects any water that may have seeped into the disposal system. Vaults are constructed above groundwater level.
ANDRA and waste generators are continuously improving the knowledge of the longer-lived radioactive content of disposed wastes. Some of the radionuclides are difficult to measure, and a scaling factors methodology is implemented. This content determines long-term safety. Some wastes (for example wastes that contain chloride-36) have to be diverted to a more appropriate disposal route under development. The maximum activity of waste allowed at the facility varies by radionuclide, from 2x105 TBq for caesium-137, to 750 TBq after 300 years for alpha emitters. Thus, to comply with the license, the facility must manage the activity of the different wastes in each of the waste packages, in each of the disposal cells, and for the facility as a whole.
At the end of 2010, 243,225 m3 of waste packages have been disposed of. Since site commissioning, every actor has been aware that a disposal facility should be considered a rare resource and should be spared as much as possible. Deliveries of low and intermediate level short-lived wastes have been indeed reduced by a factor of about three since 1989, from 35,000 to 12,000 m3 per year. Centre de l’Aube closure is therefore forecast for between 2040-2050.
The first years of operation showed that the standard types of waste packages that are accepted could meet most of waste generators’ needs. However it has emerged that occasionally large component disposal is needed. The option of removing some dismantled material whole instead of in pieces can reduce dose exposure for workers involved in decommissioning operations. ANDRA proposed accommodating some large components in standard vaults or in dedicated vaults; 41 reactor vessel heads are presently received in vaults with specific handling equipment. But the value of this disposal mode should be assessed not only with regards to decommissioning works but also to transportation and disposal. It might not be appropriate to dispose of such items if their capacity consumption would be much higher than standard packages. A general doctrine, involving decommissioning operators, transporters, disposal operators and regulators, has to be established to assess the relevance of large component disposal.
Centre de Morvilliers
The development of a very low level waste disposal facility is a consequence of French radwaste regulation (see also NEI February 2009 p22-24). Pursuant to the regulation, every French nuclear facility must separate any sector where waste is actually or likely to be contaminated or activated (a nuclear waste zone) from all other sectors where there is no waste-contamination or activation risk (a conventional waste zone). The need for a safe and cost-effective disposal facility increased with the development of decommissioning programmes for the three main French waste generators: EDF, CEA and Areva. One basic principle of repository design was to comply with regulations governing disposal facilities for non-radioactive hazardous waste. By applying such a principle, it is possible to accommodate both radiotoxic waste and toxic chemicals. Containment therefore relies on the properties of a low-permeability surface clay layer in which the repository is built.
Within the clay layer, trenches are excavated. Sides and bottom are protected by a watertight membrane. The waste is piled over the membrane, while a mobile roof protects operations throughout loading. Trenches are backfilled and sealed with the same membrane. The repository is ultimately covered with clay. After operations, a post-closure monitoring phase of approximately 30 years is planned.
ANDRA selected a suitable site in the village of Morvilliers, Aube District, close to the Centre de l’Aube disposal facility, to allowing for synergies between both facilities. A clay layer varying between 15 and 25 m in thickness was identified. The licensed capacity of the facility is 650,000 m3, or 750,000 tons. Although the maximum activity permitted varies by radionuclide as at Centre de l’Aube, the maximum mean activity cannot be higher than 10 Bq per gram.
The annual disposed volume of waste is presently 31,000 m3. About a quarter of the disposal capacity is already used, with 174,384 m3 disposed of by the end of 2010. The facility can also accommodate large components.
The principle of waste zoning implies that a large part of the waste has a very low activity and, as a matter of fact, there is sometimes only a presumption of contamination. Therefore the rationale for the disposal of significant quantities of metallic wastes can be questionable, as these pieces may not be contaminated, or be easily decontaminated. Recycling of metals within the nuclear industry, for instance in disposal structures, would be a more appropriate option. This approach is under study.
For 40 years the disposal of the major part of the volume of radioactive waste that is generated in France has become a common practice. The conceptual design of surface disposal facilities with regard to safety has progressed since 1969. One important milestone was the issue of basic safety rules. These safety rules are still the foundations for the design of the present facilities. The Centre de la Manche disposal system was continuously improved. The improvement was not only related to the design of the disposal vaults but also to the acceptance process, with the development of waste packages specifications. The Centre de l’Aube disposal facility superseded Centre de la Manche in 1992 and benefited from Centre de la Manche experience. The handling tools and conditioning equipment were updated according to the technologies available at the time of construction. Due to new regulations on waste zoning in 1999, and to deal with waste generation by decommissioning programmes, a new disposal route was implemented for very low radioactive waste.
Gérald Ouzounian, Michel Dutzer and Patrice Torres, ANDRA, Agence Nationale pour la Gestion des Déchets Radioactifs, 1-7 rue Jean Monnet 92298 Chatenay-Malabry, FranceRelated ArticlesDisposal plans (part 4: low- and intermediate-level waste) Areva regains contract for operation of French repositoryTablesTable 1: Water collected in the Centre de la Manche underground gallery