Containment decompression-filtering system in French PWRs

As part of the plan to improve the safety of French PWRs, Electricite de France (EDF) has had to take additional steps to deal with situations beyond the design basis accident. The situations which are considered to be within the limit of a design basis accident are covered by what are called ''H'' procedures, which aim to prevent any risk of serious fuel degradation. These procedures have made it possible to reduce considerably the residual risk. Nevertheless, the authors study extreme case procedures intended to facilitate the implementation of emergency plans and to ensure better control of the containment of radioactive substances during highly improbable situations following major damage to the reactor core. In response to requests made by the French safety authorities, EDF has studied the possibility of installing an additional decompression-filtering device which was not planned at the design stage. The device selected makes use of a penetration already existing in the containment. It includes isolating valves and control elements designed for the situations envisaged, a filtering tank and removal of gases filtered at the common control point for gaseous effluent from the facility. Its installation, which is designed to facilitate the implementation of emergency plans and to limit any release of radioactive substances during serious accidents, therefore complements the traditional safety procedures in France. (author)