BWR type reactors

Purpose: To uniformly overflow the cooling water from the reactor core injection system nozzle upon loss of coolant accidents in a BWR type reactor, thereby reflooding the reactor core in a short period of time. Constitution: Closing plates are attached above the reactor cover bypasses to eliminate the shrouds covering the periphery of the reactor core portion, so that coolants passing through the reactor core bypasses flow radially in the reactor portion during normal reactor operation. The upper portion of the closing plates forms the coolant receiving portion, above which a injection system nozzle is situated at a position higher than the channel box, so that coolants can be injected selectively. Upon loss of coolant accidents, the coolants uniformly uprise in the receiving portion and overflow from the upper end of the channel box along the inner wall to the inside of the reactor core. Thus, the reactor core can be re-flooded at an early stage, by which the feed rate of water can be decreased to reduce the volume. (Kamimura, M.)