A feasibility study on feed and bleed for pressurized water reactors

By injecting coolant with a high pressure emergency core cooling system, and removing the heated/ vaporized fluid by way of the pressurizer power operated relief valve, primary feed and bleed cooling denotes an operation whereby reactor core cooling is maintained. This paper presents the results from an experimental and analytical study that includes a simplified analysis of mass and energy balances associated with the feed and bleed, examination of test data from the Semiscale system, RELAP5 code analyses of both Semiscale and a four-loop Westinghouse plant, and the primary coolant system behavior for a transient that leads to the need for feed and bleed. Examination of the parameters that govern a stable feed and bleed operation identifies four key parameters such as: core decay heat, cooling water injection capacity, power operated relief valve (PORV) energy removal rate, and PORV mass removal rate. A simplified analytical approach to determining if stable feed and bleed is feasible, has been developed and corroborated by experimental data and computer code calculations. The Semiscale tests have not only provided test data for code assessment, but also have identified the factors influencing the PORV discharge, which is the most variable of the boundary conditions influencing feedmore » and bleed. The RELAP5 computer code has demonstrated the capability of predicting the Semiscale experiments, and when applied to a four-loop Westinghouse plant has indicated that primary feed and bleed is a viable cooling mechanism. This has also been shown by using the simplified analytical method.« less