As with the PWRs, decommissioning begins with the removal of the nuclear fuel, which removes 99% of the radioactivity present in the installation. As the reactors have relatively high thermal power (all greater than 250 Megawatts thermal – MWth), their decommissioning requires the use of remotely operated means in certain highly irradiating zones, particularly in the vicinity of the reactor core. The GCRs have the particularity of being extremely massive and large-sized reactors, necessitating innovative cutting and access techniques under highly irradiating conditions. The decommissioning of these reactors will oblige EDF to manage significant volumes of waste. The final disposal route for some of this waste is currently being determined, such as the graphite bricks, representing some 15,000 tonnes of waste that will be produced, for which disposal appropriate for low-level long-lived nuclear waste (LLW-LL) is envisaged. Decommissioning of the prototype heavy water reactor (EL4-D) on the Brennilis site has been slowed down, firstly due to the lack of prior experience in the decommissioning techniques to use, and secondly due to difficulties concerning the Conditioning and Storage Facility for Activated Waste (Iceda, see the “Regional Overview” in the introduction to this report) which must take in some of this decommissioning waste. Given that Iceda is now up and running and the reactor building decommissioning scenario is established, decommissioning of the installation should start again in the coming years. 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) at Saclay (BNI 49), the Chemical Purification Laboratory (LPC) at Cadarache (BNI 54), the Irradiated Materials Plant (AMI) at Chinon (BNI 94) and the “Procédé” (Process) laboratory at Fontenay-aux-Roses (BNI 165). 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 intermediated-level, long-lived waste (ILW-LL) and waste without a management route (such as non-incinerable oils and organic liquids, or waste containing potentially water-soluble mercury). 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, which makes the decommissioning and clean-out operations longer and more complex. 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. 3. 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. 2.2.2 Research reactors Eight experimental reactors are in final shutdown status at the end of 2022: Rapsodie (sodium-cooled fast neutron reactor), Masurca, Éole and Minerve (critical mock-ups), Phébus (experimental reactor), Osiris and Orphée (“pool” type reactors) and Isis (training reactors). The training reactor Ulysse was delicensed in 2022. 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. 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 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(3), the Strasbourg University Reactor – RUS, Ulysse) and abroad. Their decommissioning usually spans about ten years, but the large number of installations to decommission simultaneously may lead to significantly longer prospective decommissioning durations for some of the CEA’s reactors. After clean-out of the activated or contaminated areas and subsequent removal of all the radioactive waste to appropriate disposal routes, the majority of these reactors were demolished and the waste sent to conventional waste disposal routes. 2.3 The front-end “nuclear fuel cycle” facilities Two front-end “nuclear fuel cycle” facilities are undergoing decommissioning. They are located on the Tricastin site, one specialising in uranium enrichment by gaseous diffusion (GeorgeBesse I plant – BNI 93), the other in uranium conversion (former Comurhex plant – 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 contamination. 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 (such as chlorine trifluoride and hydrogen fluoride, and uranium itself): 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.). ASN Report on the state of nuclear safety and radiation protection in France in 2022 341 • 13 • Decommissioning of Basic Nuclear Installations 13 01 07 08 AP 04 10 06 12 14 03 09 05 11 02
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