To respond to seismic and other natural hazard events, designers of the Japan Sodium-cooled Fast Reactor (JSFR), an advanced loop-type reactor, are planning to adopt a steel-plate reinforced concrete structure reactor building and an advanced seismic isolation system to strengthen this building. The design changes have been initiated by lessons learned from the Fukushima Daiichi nuclear power plant (Fukushima I NPP) accident. These enhancements to the design are to ensure that the JSFR structure can withstand external hazards and a severe accident. This evaluation and countermeasure study of external hazards and severe accident response by JSFR are based on the JSFR design before the Fukushima I NPP accident (2010 JSFR design).

The method to evaluate the influence of external hazards on the JSFR design has applied Japanese codes and standards to show that the 2010 JSFR design of the building can withstand external hazards without additional countermeasures. And, for extreme conditions, few countermeasures are needed; however, the countermeasures considered have limited impact on the JSFR design because they do not significantly change the reactor building design.

This paper gives a detailed evaluation of the countermeasures for the external hazards and severe accidents that could impact the JSFR building.