ASN Report 2020

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 f rom the treatment. The sludge in STE2 is therefore composed of the precipitates which f ix the radiological activity, and is 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 in “C5” packages for sub- sequent disposal in a deep geological repository. ASN authorised the first phase of the work to retrieve the STE2 sludges in 2015 and the Decree authorising the creation of the effluent treatment station STE3 was modified by the Decree of 29 January 2016, to allow the implementation of the STE2 sludge treatment process. At the end of 2017 however, Orano Cycle informed ASN that the process chosen for treating the sludges in STE3 could lead to diff iculties in equipment operation and maintenance. Orano Cycle proposed an alternative scenario using centrifugation and in August 2019 it submitted a Safety Options Dossier (DOS), which is however based on 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. The DOS was to be revised, particularly in the fundamental options of the project concerning effluent treatment, discharges into the environment and control of the fire risk. In 2020, ASN began examining the new DOS submitted by Orano in July 2020 and providing additional information, particularly on the subjects relating to reactivity of the sludge and treatment of the effluents. ASN also continued examining the application for authorisation to install recovery equipment on the roofs of the STE2 facility silos, focusing particular attention on the f ire risk, the control of which is not fully demonstrated. ASN is still waiting for additional information on this latter subject. Silo 130 Silo 130 is a reinforced concrete underground storage facility, with 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 f ire which forced the licensee to flood the waste. The leak-tightness of the water-filled silo is only ensured at present by a single containment barrier consisting of a steel “skin”. Silo 130 is monitored by a network of piezometers situated nearby. The scenario for retrieving and packaging this waste comprises four stages: • 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 Cycle has built a retrieval unit above the pit containing the waste and a new building dedicated to the storing and packaging operations. In 2020, preparation of the waste retrieval operations continued and the milestone of f illing the f irst drum of waste retrieved from silo 130 was crossed. After a prolonged shutdown of the facilities due to the lockdown imposed for management of the health crisis, and the integration of material modif ications before resuming operations, including replacement of the rake cables, Orano resumed operation in October 2020 after having sent the first shipment of drums to the solid waste storage/removal from storage facility (E/D EDS) on the La Hague site. The safety issues associated with silo 130 Silo 130 was designed and built in accordance with the safety requirements in effect in the 1960’s. Today, the civil engineering structure of silo 130 is weakened by ageing and by a fire that occurred in 1981. Furthermore, part of the waste that was initially stored dry is now submerged in a large volume of water that served to extinguish the 1981 fire. 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 therefore concerns the dispersion of radioactive substances into the environment (infiltration of contaminated water into the water table). 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. ASN Report on the state of nuclear safety and radiation protection in France in 2020 81 REGIONAL OVERVIEWOF NUCLEAR SAFETY AND RADIATION PROTECTION NORMANDIE