Reactor cooling system in BWR type reactor

The present invention is suitable to removal of after-heat in a reactor core and core cooling upon accidents of a BWR type reactor. Namely, the cooling system comprises one static core spraying system having 100% capacity necessary for maintaining core flooding and two dynamic core spraying systems having 50% capacity necessary for maintaining core flooding. If the level in a reactor pressure vessel lowers, the two dynamic core spraying systems start operation. Then, water of a pressure suppression pool is injected into the reactor core pressure vessel. Subsequently, when the pressure in the reactor pressure vessel is reduced, the static core injection system operates. Then, water of the gravitational dropping type static core cooling injection system is injected gravitationally into the reactor pressure vessel. This cooling system enables maintenance for the dynamic core injection system during normal operation, so that multiple failures, if should occur, can be coped with by the operation of the static core injection system. Further, the static core injection system operates only when the dynamic core injection system fails to operate. (I.S.)