LOSS-OF-NORMAL-FEEDWATER SENSITIVITY STUDIES FOR AP600 BEHAVIOR CHARACTERIZATION

Activity concerning the development of a RELAP5/MOD3 model to simulate the Westinghouse Electric Corporation AP600 is summarized. The aim is to gain initial insight into the capability of RELAP5 to simulate the behavior of AP600 safety features. A-loss-of-normal-feedwater event i s studied. Of the transients that must be investigated, this transient has been chosen to be one of the most relevant because the response o f the AP600 to a loss-of-normal-feedwater event differs significantly from that of current pressurized water reactors in the extensive use o f passive safety features peculiar to the AP600. Also, strong interact ions among the AP600 safety systems, which should be further analyzed to permit full optimization of the system actuation logic and operatio n, are shown. Finally, a loss of normal feedwater without reactor scra m, performed to investigate short-term plant behavior, shows that the pressure peak is affected by critical discharge flow coefficients appl ied to the pressurizer safety valves, while a relatively small reducti on of the pressure peak is observed when both heat exchangers of the p assive heat removal system are operating as opposed to the case in whi ch only one is available. The data used for this study ard derived fro m the Standard Safety Analysis Report configuration of the Westinghous e AP600 as of 1992.