To improve economy by increasing coolant flow without leading to increased core height and providing a forced circulation equipment such as pumps.
A natural coolant circulation type reactor core 1 heated by fission energy is cooled by coolant 2, which is heated, ascends upward from the core 1 by convection and gives the heat to a steam generator 3 provided upper side of the core 1. The cooled coolant 2 descends from the steam generator 3 to the core 1 side by convection and contributes again to cooling of the core 1 by the natural circulation in the reactor vessel 4. The reactor vessel 4 is pressurized so that the heated coolant does not boil. Bubbles 17 are formed by supplying gas 16 in the coolant in the core 1 side so that bubbles 17 accompany the coolant ascending upward from the core 1 side and accelerate the up-flow velocity of the coolant 2.
KOGA ATSUSHI
SUZUTA TADAHIKO
YOSHIDA ZENICHI
