BWR type reactor

Purpose: To provide the subject reactor, wherein the power density is decreased, the reactor is operated at high void quality, the average energy of neutron is increased to improve the conversion ratio and also increase fuel economy, and, at the same time, simplification of the core operating method and improvement in the plant utilization factor are achieved. Constitution: The reactor is operated at more than 17% of the core outlet quality. The core outlet quality of 17% can be materialized by making the coolant flow rate per fuel assembly 45.8 t/h, that is, about 72% of the conventional coolant flow rate of 63.6 t/h in the case where the power per fuel assembly is made 3.9 MW. When the core quality is made more than 17%, the coolant quality in the upper half resion of the core is at least 8.5% or above, and the coolant void coefficient becomes 66% or more at the upper half of the core. (Yoshihara, H.)