PWR type reactor and operation method therefor

In a PWR type reactor, a low temperature pipeline is connected to a coolant inlet nozzle and a high temperature pipeline is connected to an exit nozzle of coolants of a reactor container, and the low temperature pipeline and the high temperature pipeline are connected by way of a bypass pipe. In the former half of the operation cycle, an opening/closing valve is opened to bypass the coolants, and in the latter half of the operation cycle, the opening/closing valve is closed to elevate the pressure in primary coolants. In the former half of the fuel cycle, the reactor core flow rate is reduced to cause boiling in the reactor core, and a neutron spectrum is shifted to the high energy side to promote generation of plutonium. In the latter half of the cycle, the reactor core flow rate is increased to form a single phase flow, and the neutron spectrum is shifted to the low energy side thereby effectively burning plutonium generated in the former half of the cycle. The former half of a primary system pressure is kept at such a level as capable of maintaining subcooling upon joining with bypass flow, in the former half, while the primary system pressure is elevated to keep subcooling also in the reactor core in the latter-half cycle. (N.H.)