2.1.2 Nuclear power reactors other than Pressurised Water Reactors The nuclear power reactors that are not PWRs are all industrial prototypes. These comprise the first-generation Gas-Cooled Reactors (GCRs), as well as the EL4-D heavy water reactor on the Brennilis site, and the sodium-cooled fast breeder reactors Phénix and Superphénix. The decommissioning of these reactors is characterised by the lack of prior experience in France or elsewhere in the world, and the fact that when they were designed, the prospect of their future decommissioning was not as fundamental a concern as it may have been for the more recent reactor series. In view of their unique nature, specific and complex operations have to be devised and carried out to decommission them. Furthermore, some of these reactors have been shut down for several decades, which has led to loss of knowledge of the installation and its operation and loss of the associated skills. 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 for 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 OEF concerning the decommissioning techniques to be used, 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 in service and the reactor building decommissioning scenario has been established, decommissioning of the installation will resume in 2041, to achieve complete dismantling of the facility by the end of 2041, as regulated by Decree 2023-898 of 26 September 2023. 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. 2. 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. 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), waste without a disposal route (such as non-incinerable organic oils and liquids, or waste containing potentially water-soluble mercury compounds). 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. 2.2.2 Research reactors Eight experimental reactors are in final shutdown status at the end of 2023: Rapsodie (sodium-cooled fast neutron reactor), Masurca, Éole and Minerve (critical mock-ups), Phébus (test reactor), Osiris and Orphée (“pool” type reactors) and Isis (teaching reactor). The Ulysse training reactor 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 via an appropriate route. There is a considerable amount of OEF for the research reactors, given the decommissioning of numerous similar installations in France (Siloé, Siloette, Mélusine, Harmonie, Triton(2), the Strasbourg University Reactor – RUS, Ulysse) and abroad. Their decommissioning usually spans about ten years, but the large number of installations to be decommissioned simultaneously may lead to significantly longer prospective decommissioning durations for some of 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 (Georges Besse 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 protection issues are therefore to a large extent linked to the risk of internal contamination. ASN Report on the state of nuclear safety and radiation protection in France in 2023 351 • 14 • Decommissioning of Basic Nuclear Installations 14 05 15 08 11 04 06 07 13 AP 03 10 02 09 12 01
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