The Chemistry

Abstract

The sodium specific chemical properties lead, on a fast reactor, to significant specificities, which were already discussed in the Chaps. 13 “The Sodium/Water Reactions”, 14 “Sodium Leaks and Fires”, 17 “The Materials”, etc. In this chapter, it is essentially dealt with monitoring and keeping the sodium quality during the reactor life. The reactor sodium contains initial impurities related to fabrication specifications. Pollution sources do exist during reactor operations:

• air and moisture ingresses during some handling operations,

• diffusion of the hydrogen produced by the aqueous corrosion of steam generator walls and the partial decomposition of the hydrazine used to treat the steam generator water,

• diffusion of the tritium produced by the neutron activity.

Moreover, incidental situations may occur, leading to additional pollutions:

• fuel clad failures, introducing fission products and fuel particles,

• air ingress,

• sodium-water reaction in the steam generators,

• rotating plug sealing fluid ingress (liquid metal seal),

• pump packing-box oil ingress, or lubrication greases, etc.

The sodium quality deterioration may have consequences in terms of material corrosion, of sodium and structure radio-contamination and of local plugging risks. During Superphenix operations, there were neither clad failures nor sodium-water reaction. The only observed major sodium pollution was related to air ingress, in June 1990. This incident is analysed with the related experience feedback. Cold traps and plugging indicator operations, at Superphenix, enable to keep good the sodium purity and bring an experience feedback on these equipment and their use.