NATURAL CIRCULATION BOILING WATER REACTOR

PROBLEM TO BE SOLVED: To provide a natural circulation boiling water reactor to which a thermal margin evaluation method for a core proven in a forced circulation boiling water reactor and having a high accuracy can be applied. SOLUTION: The natural circulation boiling water reactor 1 comprises a core 7 loaded with a plurality of fuel assemblies 21 and a chimney 11 installed above the core 7 and having channel bulkheads 11b guiding a two-phase (gas-liquid) flow ascending from the core 7 to a plurality of vertical lattice channels 11a, and an equalizing space 35 not having the channel bulkhead 11b is provided below the chimney 11. Therefore, the distribution of the flow to the individual fuel assemblies 21 can be calculated by the calculation of the difference in pressure between the tip end and the bottom end of the core 7 without need of the void ratios of the individual lattice channels 11a. COPYRIGHT: (C)2007,JPO&INPIT