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, in addition to the 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.). 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 operated by Orano, are 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, BNI 33, called “UP2-400” standing for “Production Unit No. 2 – 400 tonnes”, was definitively shut down on 1 January 2004 along with its support facilities: Effluent Treatment Station No. 2 (STE2) and the Spent fuel reprocessing unit (AT1 – BNI 38), the Radioactive sources fabrication unit (ELAN IIB – BNI 47) and the “High Activity Oxide” (HAO) unit, created for reprocessing fuels from the “light water” reactors (BNI 80). Some of these facilities experienced accidents which contaminated the premises and their near environment, such as the fire in silo 130 belonging to BNI 38, in 1981. Unlike the direct on-line packaging of the waste generated by the plants in operation (plants treating irradiated fuel elements from light water nuclear reactors – UP2-800 and UP3-A), most of the waste generated by the first reprocessing plant was stored without treatment or conditioning. Decommissioning is therefore carried out concomitantly with the legacy WRC operations. About ten projects of this type are currently in progress in the old facilities (silos STE2, 115 and 130 in BNI 38 and the HAO silo in BNI 80). They will span several decades and are a prerequisite to the complete decommissioning of these facilities, whereas the decommissioning of the process parts of the plant is continuing with more conventional techniques. 2.5 THE SUPPORT FACILITIES (STORAGE AND PROCESSING OF RADIOACTIVE EFFLUENT AND WASTE) Many of these facilities, most of which were commissioned in the 1960’s and whose level of safety did not comply with current best practices, have been shut down. Old storage facilities were not initially designed to allow the removal of the waste, and in some cases they were seen as being the definitive waste disposal site. Examples are the silos at SaintLaurent-des-Eaux (BNI 74), the pits, trenches and hangars of the radioactive waste storage area (BNI 56), the pits of the ZGDS (BNI 72) and the Support facility (BNI 166). Retrieval of the waste from these facilities is complex and will span several decades. The waste must then be packaged and stored again in safe conditions. New packaging and storage facilities are thus either planned or actually under construction. The STEs for their part have been shut down due to their ageing or because the facilities producing the effluents treated in these units have stopped functioning. Examples include BNI 37-B at Cadarache and STE2 at the La Hague plant (BNI 38). The difficulties associated with decommissioning of the effluent treatment stations are closely linked to their shutdown conditions, particularly the emptying and rinsing of their tanks. The decommissioning of these support facilities raises many issues. Firstly, poor knowledge of the operating history and the state of the facility to be decommissioned (taking account of the corrosion of waste drums or pollution of soils resulting from significant events that occurred when in service, for example) necessitates prior characterisation of the stored legacy waste and of the sludges or deposits present in certain tanks. Moreover, 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 heterogeneous, as it 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. 3 ASN actions related to facilities being decommissioned: a graded approach 3.1 THE GRADED APPROACH ACCORDING TO THE RISKS OF THE FACILITIES ASN ensures the oversight of facilities undergoing decommissioning, as it does for facilities in operation. More specifically, the BNI System also applies to definitively shut down facilities. ASN implements an approach that is proportional to the extent of the risks or drawbacks inherent in the facility. The risks with facilities undergoing decommissioning differ from those for facilities in operation. For example, the risks of significant off-site discharges decrease as decommissioning progresses because the quantity of radioactive substances decreases. Consequently, the requirements relating to the control of risks and impacts are proportionate to the risks inherent in the facilities. ASN thus considers that it is generally inappropriate to start significant reinforcement work on a facility undergoing decommissioning, on condition that the decommissioning operations reduce the sources of danger in the short term. ASN Report on the state of nuclear safety and radiation protection in France in 2023 359 • 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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