The decommissioning of the sodium-cooled reactors (Phénix and Superphénix) has met with no major technological obstacles. The specific challenges lie chiefly in the control of the fire risk due to the presence of sodium and the safety of its treatment processes. 2.2 Research facilities 2.2.1 Research laboratories Four research laboratories are currently undergoing decommissioning or preparation for decommissioning. These are the High Activity Laboratory (LHA –BNI 49) at Saclay, the Chemical Purification Laboratory (LPC –BNI 54) at Cadarache, the Irradiated Materials Plant (AMI –BNI 94) at Chinon and the “Procédé” laboratory (BNI 165) at Fontenay-aux-Roses. These laboratories, which began operating in the 1960s, were dedicated to research to support the development of the nuclear power industry in France. These very old facilities are all confronted with the issue of managing the “legacy” waste, stored on site at a time when the waste management routes had not been put in place, such as intermediate level, long-lived waste (ILW-LL) and waste without a disposal route (such as asbestos, mercury, etc.). Moreover, incidents occurred during their operation, contributing to the emission of radioactive substances inside and outside the containment enclosures and to the varying levels of pollution of the structures and soils, making the decommissioning operations long and difficult. One of the most important steps in the decommissioning of this type of facility, and which is sometimes rendered difficult due to incomplete archives, therefore consists in inventorying the waste and the radiological status of the facility as accurately as possible, in order to define the decommissioning steps and the waste management routes. 2.2.2 Research reactors Nine experimental reactors are in final shutdown status at the end of 2021: Rapsodie (sodium-cooled fast neutron reactor), Masurca, Éole and Minerve (critical mock-ups), Phébus (experimental reactor), Osiris and Orphée (“pool” type reactors), Ulysse and Isis (training reactors). These reactors are characterised by a lower power output (from 100 Watts thermal –Wth to 70 MWth) than the nuclear power reactors. When they were designed back in the 1960s to 1980s, the question of their decommissioning was not considered. Furthermore, one of the major decommissioning problems is the loss of memory of the design and operation of the installation. Therefore maintaining skills and the installation characterisation phase to determine its initial state (state of the installation at the start of decommissioning) are of vital importance. At the time of decommissioning, these installations usually present a low radiological source term, as one of the first operations after final shutdown consists in removing the spent fuel. One of the main challenges comes from the production and management of large volumes of VLL waste, which must be stored then disposed of via an appropriate route. There is a considerable amount of decommissioning experience feedback for the research reactors, given the decommissioning of numerous similar installations in France (Siloé, Siloette, Mélusine, Harmonie, Triton(4), the Strasbourg University Reactor –RUS) and abroad. Their dismantling time frames usually span about ten years. Most of these reactors have been demolished and the waste disposed of via conventional routes after clean-up of the activated or contaminated zones. 4. Triton was one of the first very compact and very flexible pool type research reactors called “MTR” (Material Test Reactor). Triton (6.5 MWth) was installed in Fontenay‑aux‑Roses in 1959. 2.3 The front-end “nuclear fuel cycle” facilities Two front-end “nuclear fuel cycle” facilities are undergoing decommissioning. They are situated on the Tricastin site, one specialising in uranium enrichment by gaseous diffusion (BNI 93), the other in uranium conversion (BNI 105). The only radioactive materials used in these plants were uraniumbearing substances. One of the particularities of these facilities therefore lies in the presence of radioactive contamination associated with the presence of “alpha” particle-emitting uranium isotopes. The radiation exposure risks are therefore largely linked to the risk of internal exposure. Furthermore, these are older facilities whose operating history is poorly known. Determining the initial state, particularly the pollution present in the soils beneath the structures, therefore remains an important issue. Moreover, the industrial processes implemented back then involved the use of large quantities of toxic chemical substances (uranium, chlorine trifluoride and hydrogen fluoride, for example), and the containment of these chemical substances therefore also represents a risk on these facilities and can necessitate the deployment of dedicated means (ventilation, containment air locks, respiratory protection masks, etc.). 2.4 The back-end “nuclear fuel cycle” facilities The back-end facilities of the “nuclear fuel cycle” are the spent fuel storage pools, the spent fuel reprocessing plants and the facilities for storing waste from the treatment process. These facilities are operated by Orano and situated on the La Hague site. The first processing facility at La Hague was commissioned in 1966, initially for reprocessing the fuel from the first-generation GCRs This facility called “UP2-400” (BNI 33) standing for “Production Unit No. 2-400 tonnes”, was definitively shut down on 1 January 2004 along with its support facilities: namely the effluent treatment station STE2 and the spent fuel reprocessing facility AT1 (BNI 38), the radioactive source fabrication facility ELAN IIB (BNI 47) and the “High Activity Oxide” facility (HAO), built for reprocessing the fuels from the “light water” reactors (BNI 80). Unlike the direct on-line packaging of the waste generated by the UP2-800 and UP3-A plants in operation, most of the waste generated by the first reprocessing plant was stored without treatment or packaging. Decommissioning is therefore carried out concomitantly with the legacy Waste Retrieval and Packaging (WRP) operations. Taking into account the quantities, the physical and chemical forms and the radiotoxicity of the waste contained in these facilities, the licensee must develop means and skills that involve complex engineering techniques (radiation protection, chemistry, mechanics, electrochemistry, robotics, artificial intelligence, etc.). In effect, this waste is highly irradiating and comprises structural elements from fuel reprocessing, technological waste, rubble, soils and sludge. Some of the waste has been stored in bulk with no prior sorting. The retrieval operations therefore require remotely operated pick-up means, conveyor systems, sorting systems, sludge pumping and waste packaging systems. The development of these means and carrying out the operations under conditions ensuring a satisfactory level of safety and radiation protection represent a major challenge for the licensee. Given that these operations can last several decades, the management of ageing of the facilities is also a challenge. ASN Report on the state of nuclear safety and radiation protection in France in 2021 333 13 – DECOMMISSIONING OF BASIC NUCLEAR INSTALLATIONS 08 07 13 04 10 06 12 14 03 09 05 11 02 AP 01
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