Disposal of Creys Malville sodium

This document describes the fate decided for the sodium wastes from Superphenix and succinctly describes the method adopted for treating reactor sodium. After the declaration to the French National Assembly on June 19, 1997, of the decision to finally shut down the Creys power plant, the first structured strategic reflection for definitive shutdown began in February 1998. One of the main aims of this reflection was to prove the technical feasibility of this dismantling based on the assumption of reasonable costs and time limits. In this context of 'technical doubt', a very determined attitude had to be adopted. At the beginning of 1998, it was decided to make a total commitment to this project (fast studies and execution of sodium treatment and dismantling) while at the same time observing the safety and regulatory aspects. This option also met a keen requirement of the Department of the Environment for a technically irreversible operation so that reactor restart would no longer be an option. The decree of 31/12/98 finalized the immediate and definitive shutdown of Creys nuclear power station and authorized unloading of the fuel. It also covers sodium removal and storage operations and the dismantling of the non-nuclear installations within the framework of a safety report and general rules for monitoring and maintenance approved by the DSIN (French Nuclear Installations Safety Authority). At the EDF-CIDEN, a so-called reference scenario based on the discharge of sodium sulphate salts to the Rhone river (reflecting the Scottish approach used in the sodium disposal process, which is economically less expensive but 'sensitive' in terms of its acceptance by the media and the environmental lobby) has been developed and alternative solutions put forward. This scenario requires the installation of a primary sodium draining system as well as the treatment of certain significant retentions in the vessel, and the construction of a 'reactor' to transform the sodium into caustic soda. This would be of the same type as on the Sodium Disposal Process for PFR on Dounreay site, based on the principle developed by the CEA for the Rapsodie programme (NOAH process). An early commitment to sodium draining before the very specific competence for this complex operation are lost was another strong additional incentive drawn from the experience feedback from other sites. Faced with the risk relating to the discharge into the Rhone which this scenario involves, a fallback scenario for treatment involving caustic soda cementation and long-term storage was chosen (with several possible technical options). The possibility of intermediate storage of all sodium products, which would release the reactor from the monitoring requirements related to the liquid sodium, was not retained since the cost of this solution would cancel out the indirect gains made on the operating costs. In 2001, the scenario of sodium sulphate discharge into the Rhone was abandoned in favour of the scenario known as treatment by cementation. In spite of a significant difference in the cost, due to the climate surrounding the Public Inquiry File, it is no longer certain that a new application to discharge to water in this first solution would be looked at favourably or that it would be authorized within reasonable delays. This decision is consolidated by the desire on the part of EDF General Management to proceed to 'immediate' dismantling of the nine definitively shutdown nuclear sites, thereby reducing the programming for Creys Malville to a total duration of 25 years. The risk involved in an uncontrollable administrative delay therefore became unacceptable. To conclude this first part, the choice of the sodium treatment solution for Creys Malville is based on a so-called on-line drainage system (no buffer storage) using tools fabricated for this operation, followed in real time by treatment at 6 metric tonnes/day in two caustic soda transformation reactors (NOAH process) nearly identical to the SDP ones. A total of 13 860 m3 of caustic soda from primary sodium will be mixed with cement to make packages (26,400 cubes of 1m3) that will be stored on the surface since they are only very slightly radioactive (< 100 Bq/g), and this in less than 2 years