Design extension condition on PHWR accident scenario

This paper presents a combined accident scenario for a CANDU 600 Pressurized Heavy Water Reactor (PHWR) consisting of a design basis accident (DBA) and a sudden generator disconnection from the power grid. The scenario is considered in the hypothesis of a major earthquake, beyond the design basis (BDBA), which leads to the co-occurrence of both events. The analyzed DBA is the main steam header break. This event imposes a specific behavior from the power plant cooling systems, otherwise it causes the beginning of a severe accident progression which might evolve to a partially/fully damaged reactor core. The second event is a class IV main component failure analysis of one of the equipment. The class IV equipment failure already has a Guaranteed Shutdown State (GSS) condition which can't be achieved during a DBA. The analysis of design extension condition scenarios is suggested by the International Atomic Energy Agency (IAEA), following the Fukushima Daiichi Nuclear Power Plant accident in 2011 [1].