ASN Report 2018

particle-emitting uranium isotopes. The radiation exposure risks are therefore largely linked to the risk of internal exposure. Nevertheless, the fact that uranium alone is present facilitates the characterisation of the state of the facility at the start of the decommissioning operations. 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. The industrial processes 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 is an important issue on these facilities. 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 Cycle 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 Gas-Cooled Reactors. This facility, BNI 33, called UP2-400, standing for “Production Unit No. 2 – 400 tonnes” (the first reprocessing plant was UP1 situated in the DBNI of Marcoule and is currently being decommissioned), was definitively shut down on 1 January 2004 along with its supporting plants, 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 “Oxide High Activity” 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, most of the waste generated by the first reprocessing plant was stored in bulk. Decommissioning is therefore carried out concomitantly with the legacy Waste Retrieval and Packaging (WRP) operations. 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 is also a challenge. 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.). At present about ten projects of this type are underway in the former storage facilities. They will span several decades and are a prerequisite to the decommissioning of these facilities, whereas the decommissioning of the plant’s process facilities is continuing with more conventional techniques. 2.5  ̶  The support facilities (storage, effluent and waste processing) The availability of the “support” facilities (for the storage of waste and materials, waste packaging, effluent treatment, etc.) governs the performance of the waste retrieval and packaging, decommissioning and clean-out operations. These facilities must not only be available at the right time, but also be appropriate for the quantities and types of waste or effluents they will be required to treat. Many of these facilities, most of which were commissioned in the 1960’s and whose standard of safety does not comply with current best practices, have been shut down. They have not always been replaced by new facilities. 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 include the Saint-Laurent-des-Eaux silos (BNI 74), the Orano Cycle plant silos in La Hague (silos 115 and 130 in BNI 38, the HAO silo in BNI 80), the pits and trenches of BNI 56 and the wells of BNI 72 and BNI 166. Retrieval of the waste from these facilities is complicated and will extend over several decades. The waste must then be packaged and stored under safe conditions. New packaging and storage facilities are thus planned or under construction. The packaging and storage must be carried out without adversely affecting the suitability of the waste for subsequent disposal in the planned facilities. It is therefore necessary for the licensees to undertake an ambitious development programme relative to the packaging of low and intermediate-level long-lived waste. Initially, almost every site had an Effluent Treatment Station (STE) which also packaged the resulting concentrates. The ageing of the facilities or the shutdown of the effluent- producing facilities led to the shutdown of these STEs. Examples include the FAR STED, BNI 37-B at Cadarache, STE2 at the La Hague plant and the Brennilis STE. The difficulties associated with the decommissioning of the STEs are closely dependent on their shutdown conditions, particularly the emptying and rinsing of the tanks. With respect to the needs to treat the effluents from facilities undergoing decommissioning and in operation, there are significant uncertainties regarding the required capacities due to the lack of forecasting of the production of intermediate and high-level liquid waste and to the decommissioning processes used (dry or wet processes). Historically, low-level and intermediate-level liquid effluents were packaged in a bituminous matrix. This organic matrix can be used to package a wide physical-chemical and radiological spectrum of waste, but it deteriorates over time due to the radiation and produces hydrogen. The new processes aim to package effluents in a mineral matrix by cementation. Due to the difficulty in guaranteeing the quality of the matrix under all conditions, they do not - at this stage of their development allow the packaging of such a wide range of waste. The major difficulties associated with the decommissioning of the support facilities are as follows: ∙ ∙ Poor knowledge of the operating history and the state of the facility to decommission, which necessitates prior characterisation of the old waste and the analysis of samples of the sludge or deposits in the STE tanks. This characterisation necessitates firstly the development of methods and the use of specific equipment to take the samples, and secondly the availability of analysis laboratories. 342  ASN report on the state of nuclear safety and radiation protection in France in 2018 13 – DECOMMISSIONING OF BASIC NUCLEAR INSTALLATIONS