FEED WATER CONTROL SYSTEM FOR BOILING WATER NUCLEAR REACTOR

PURPOSE:To diminish occasions of scrams, by providing a first function which supposes a mass flow rate of a two phases flow pouring into a nuclear reactor dome from an upper plenum of the nuclear reactor and by providing the second function which supposes a steam quality of the two phases flow. CONSTITUTION:An overall flow rate WLP is expressed by an equation I. As a portion theta (usually around 10%) of WLP becomes a leak flow, a channel flow rate WC and the leak flow rate WB are expressed as equations II and III, respectively. Subsequently, with receiving heat from a thermal nuclear reaction at a reactor core, WC and WB turn into a two phases flow with an average quality XUP, a void ratio alphaUP and a pressure PCORE, at an upper plenum. The quality X is determined by the equation IV and the void ratio alpha is determined by the equation V. Therefore, a steam flow rate is expressed as (quality) X total flow, and the remains are given as a saturated water flow rate. In this way, through supposing the physical quantities of state (a separator inlet flow rate WUP and the quality XUP), occasions of scrams caused by a reactor water level 'high' or 'low', can be diminished.