[en] Purpose: To remove a non-condensable gas before vapor of high temperature and high pressure, which flows out at a failure of primary piping in a reactor, compresses the noncondensable gas sealed within the reactor container. Constitution: This pressure suppression device is arranged below a Dharma-shaped reactor container accomodating therein a reactor pressure vessel, and the vessel is usually connected with the pressure suppression device through more than ten bent pipes. A pool water immersion portion of a downcomer connected to the bent pipes is formed with a number of holes. The bent pipes and downcomer are provided with gas discharge valves. By the action of the thus formed holes and gas dicharge valves, the vapor of high temperature and high pressure is injected into the pool water. At the same time, the pool water may be sufficiently agitated to thereby avoid disturbances of the pool water due to uneven temperature distribution. (Yoshihara, Y.)