Fast reactor decay heat removal: approach to the safety system design in Japan and Europe

In the framework of the cooperation on fast reactor between the European and Japanese electrical utilities, the design companies responsible for the demonstration fast breeder reactor (DFBR) in Japan and the European fast reactor (EFR) have performed a comparative evaluation of the safety qualified decay heat removal systems of the two reactor designs. At the level of overall safety and concept design there is an obvious similarity between the two DHR systems. In both cases heat is removed directly from the reactor vessel primary sodium by systems designed according to a similar deterministic methodology, with a probabilistic assessment performed to demonstrate achievement of the required reliability. Nevertheless, the evaluation revealed a number of differences resulting from different national practices. These include the application of diversity and redundancy philosophy, the extent of passivity taken into account, the consequences of postulated maintenance outage on the design and the decay heat curve.