Abstracts ASN Report 2021

LEGACY WASTE RETRIEVAL AND PACKAGING OPERATIONS Unlike the direct on-line packaging of waste, as is done with the waste produced in the new UP2-800 and UP3-A plants at La Hague, the majority of the waste produced by the first UP2-400 plant was stored in bulk without final packaging. The operations to retrieve this waste are complex and necessitate the deployment of substantial means. They present major safety and radiation exposure risks, which ASNmonitors with particular attention. The retrieval of the waste contained in the old storage facilities of the La Hague site is also a prerequisite for the decommissioning and clean-out of these storage facilities. Retrieval and packaging of the STE2 sludges The STE2 station of UP2‑400 was used to collect the effluents from the UP2‑400 plant, treat them and store the precipitation sludge resulting from the treatment. The STE2 sludges are thus precipitates that f ix the radiological activity contained in the effluents and they are stored in seven silos. A portion of the sludges has been encapsulated in bitumen and packaged in stainless steel drums in the STE3 facility. Following ASN’s banning of bituminisation in 2008, Orano studied other packaging methods for the non-packaged or stored sludges. The scenario for the retrieval and packaging of the STE2 sludges presented in 2010 was broken down into three steps: • retrieval of the sludges stored in the silos of STE2 (BNI 38); • transfer and treatment, initially envisaged by drying and compaction, in STE3 (BNI 118); • packaging of the resulting pellets into C5 packages for deep geological disposal. ASN authorised the f irst phase of the work to retrieve the sludges from STE2 in 2015. The Creation Authorisation Decree for the STE3 effluents treatment station was modified by the Decree of 29 January 2016 to allow the installation of the STE2 sludges treatment process. At the end of 2017 however, Orano Recyclage informed ASN that the process chosen for treating the sludges in STE3 could lead to difficulties in equipment operation and maintenance. Orano proposed an alternative scenario using centrifugation and in August 2019 it submitted a Safety Options Dossier (DOS), which is however based on as yet insufficiently substantiated hypotheses. An inspection conducted at the end of 2019 confirmed that the project was not sufficiently mature for ASN to be able to give an opinion on this DOS. Orano submitted an update of the DOS to ASN in July 2020. This file is currently being examined. At present, the technical discussions with Orano highlight the need to further the studies of the sludge treatment and packaging processes, and the possibility of interim storage of the retrieved sludge under suitably safe conditions so that this step can be separated from their final packaging. Silo 130 Silo 130 is a reinforced concrete underground storage facility, with a carbon steel liner, used for dry storage of solid waste from the reprocessing of Gas-Cooled Reactor (GCR) fuels, and the storage of technological waste and contaminated soils and rubble. The silo received waste of this type as from 1973, until the 1981 fire which forced the licensee to flood the waste. The leak-tightness of the water-f illed silo is only ensured at present by a single containment barrier consisting of a steel “skin”. Today, the civil engineering structure of Silo 130 is weakened by ageing and by a f ire that occurred in 1981. The water is therefore in direct contact with the waste and can contribute to corrosion of the carbon steel liner, which at present is the only containment barrier. One of the major risks for this facility concerns the dispersion of radioactive substances into the environment (infiltration of contaminated water into the water table). The leak-tightness of Silo 130 is monitored by a network of piezometers situated nearby. Another factor that can compromise the safety of Silo 130 is linked to the nature of the substances present in the waste, such as magnesium, which is pyrophoric. Hydrogen, a highly inflammable gas, can also be produced by phenomena of radiolysis or corrosion (presence of water). These elements contribute to the risks of fire and explosion. The waste retrieval and packaging scenario comprises four steps: • retrieval and packaging of the solid GCR waste; • retrieval of the liquid effluents; • retrieval and packaging of the residual GCR waste and the sludges from the bottom of the silo; • retrieval and packaging of the soils and rubble. Orano has built a retrieval unit above the pit containing the waste and a new building dedicated to the storing and packaging operations. The works carried out on Silo 130 in 2021 allowed the retrieval of about twenty waste drums. These operations were initially carried out manually, then in semi-automatic mode. In view of the various technical problems encountered, the industrial commissioning step with waste retrieval in automatic mode could not be accomplished in 2021. Orano envisages carrying out this step in early 2022. HAO silo and Organised Storage of Hulls The Oxide High Activity Facility –HAO (BNI 80) ensured the first steps of the spent nuclear fuel reprocessing process: reception, storage, then shearing and dissolution. The dissolution solutions produced in BNI 80 were then transferred to the UP2-400 industrial plant in which the subsequent reprocessing operations took place. BNI 80 comprises: • HAO North, spent fuel unloading and storage site; • HAO South, where the shearing and dissolution operations were carried out; • the “filtration” building, which accommodates the filtration system for the HAO South pool; ABSTRACTS – ASN Report on the state of nuclear safety and radiation protection in France in 2021 79 REGIONAL OVERVIEW OF NUCLEAR SAFETY AND RADIATION PROTECTION NORMANDIE