PURPOSE: To form a natural circulating flow of coolant when a reactor is stopped, and increase the heat removing quantity by providing each passage for normal flow and back flow on a shielding assembly charged on the circumferential area of a core.
CONSTITUTION: At general operation of the reactor, a coolant having a small flow rate to a fuel assembly 16 flows in a &shielding assembly 21 from a low pressure plenum 10 to an upper plenum 4 through a low pressure passage and a not-mat flow passage. When the reactor is stopped, the coolant heated by the decay heat of a core 1 is raised from the assembly 16 inner part to the plenum 4 through a clearance part 35. The coolant partially gets into a heat exchanger 15 through a coolant inlet port 17 and flows out from a coolant outlet port 18, and partially descends 19 in the plenum 4. These coolants descend in the back flow passage of the assembly 21 and flow out to the core 1 peripheral part through the outlet. On the other hand, the coolant in the core 1 center part is heated and raised, and the outflown coolant is sucked into the core 1 center part this ascending flow, and raised in the clearance part 35. Thus, a natural circulating flow of coolant by way' of the assembly 21 is formed, and the decay heat removing quantity is increased.
KASAI SHIGEO
ONUKI KOJI
KUBOTA KENICHI
WAKAMATSU MITSUO
