ASN Report 2020

2. Situation of nuclear facilities undergoing decommissioning – specific challenges At the end of 2020, 36 nuclear facilities in France are definitively shut down or undergoing decommissioning. It is planned to shut down some ten more facilities in the coming years (see map page 349). These facilities are varied (nuclear power reactors, research reactors, fuel cycle facilities, support facilities, etc.) and the decommissioning challenges can differ greatly from one facility to the next. These challenges are, however, all linked to the large quantity of waste to be managed during decommissioning. The risks for safety and radiation protection are all the higher if the facilities contain legacy waste; this is the case with the Orano former spent fuel reprocessing plants or the CEA’s old storage facilities. 2.1  Nuclear power reactors 2.1.1 Pressurised water nuclear power reactors The first Pressurised Water Reactor (PWR) undergoing decom­ missioning in France is the Chooz A reactor (BNI 163). This is a small model compared with the 56 nuclear power reactors in operation. Decommissioning of Chooz A has been authorised by Decree since 2007 and presents some specific technical difficulties due to its construction inside a cavern. This makes some operations more complex, such as the removal of large components like the steam generators. Decommissioning of the Chooz A reactor vessel and its internal components is in progress and should continue in the time frames specified in the Decree. Decommissioning of the PWRs is detailed in the box below. 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), the EL4-D heavy water reactor on the Brennilis site, and the sodium-cooled fast breeder reactors Phénix and Superphénix. 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 skills associated with these reactors. The decommissioning of these reactors is characterized by the lack of prior national or international experience. 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 thermal power of these reactors is relatively high – all greater than 250 Megawatts thermal (MWth) – their decommissioning necessitates the cutting away and removal of the activated parts of the reactor core. Remotely-operated means are therefore used in these highly irradiating zones. In view of their unique nature, specific and complex operations have to be devised and carried out to decommission them. 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, for which disposal appropriate for low-level long-lived nuclear waste (LLW-LL) is envisaged. Decommissioning of the EL4-D reactor (prototype heavy water reactor) has been slowed, firstly due to the lack of prior experience in the decommissioning techniques to use, and secondly due to unforeseen setbacks concerning the Conditioning and Storage Facility for Activated Waste (Iceda, see the Regional Overview in the introduction to this report and chapter 14). 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 decom­ missioning 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 “Process” laboratory at Fontenay-aux-Roses (BNI 165). These laboratories, which began operating in the 1960s, were dedicated to Research & Development to support the development of the nuclear power industry in France. Research laboratory decommissioning operations prior to delicensing are typically carried out in several steps: ∙ removal of the legacy or old waste; ∙ disassembly of the electromechanical equipment and the reactor containments; ∙ cleaning out of the structures and remediation of the soils polluted by the activities of the BNI, if necessary. Dismantling of the structures and civil engineering work, if applicable, can be carried out in the conventional manner after their complete clean-out. Nevertheless, in certain cases of highly contaminated structures, dismantling must be carried out during the decommissioning steps as their stability cannot be guaranteed once they have been cleaned out. In such cases, dismantling, which is carried out using techniques specific to the nuclear industry, is a step necessary for delicensing. 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 (e.g. 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, 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. This is because incomplete understanding of the initial situations and insufficient characterisation of the waste make it necessary to revise the planned steps and lead to difficulties in packaging the waste, which is counterproductive to decommissioning progress. When the waste is removed, very often to interim storage areas, and the main equipment remotely dismantled using the existing handling means, continuation of the decommissioning work usually necessitates opening the radioactive substance contain­ ment barriers in order to remove the last process or research equipment and the pipes using, among other things, more substantial cutting and handling equipment. The latter present ASN Report on the state of nuclear safety and radiation protection in France in 2020 343 13 – DECOMMISSIONING OF BASIC NUCLEAR INSTALLATIONS 13