BWR type reactor

In a BWR type reactor, a pressure suppression chamber is disposed above a reactor pressure vessel, as well as water flooding pipelines are disposed on the side of pipelines connecting the pressure suppression pool and a reactor core and a pressure vessel in an emergency reactor core cooling system, and check valves are disposed, respectively, in the midway of the pipelines. A plurality of heat transfer pipes having a heat exchanger in a dry well are disposed in a reactor container cooling system. The heat transfer pipe is connected at the inlet to a pool for supplying cooling water, and connected at the exit to the pool at the outside of the reactor container disposed above the heat exchanger. The size of the reactor container can be decreased by combining the emergency reactor core cooling system and the reactor container cooling system. After heat generated in the reactor core can be released to the outside of the reactor container by natural convection caused by the pressure suppression pool also having an effect of gravitationally dropping type emergency reactor core cooling system and by natural convection in the heat transfer pipes inserted to the lower pool. (N.H.)