THE EFFECT OF THE PRESSURISER HEATERS ON SPURIOUS MAIN SPRAY INITIATION, MSO36, SCENARIO IN A REFERENCE PLANT FIRE PRA

摘要

In this paper, a plant-specific analysis was performedusing MAAP 4.0.8 Code to evaluate the applicability ofgeneric MSO 36 scenario to a reference plant. Accordingto NEI 00-01 Revision 3, MSO 36 scenario is defined as(Spurious opening of pressurizer spray valves) AND(Inability to trip, or spurious operation of RCP) AND(Failure of Pressurizer heaters). The focus of the plantspecificMAAP analyses was to evaluate the effectivenessof the pressurizer heaters in preventing spurious safetyinjection signal due to low pressurizer pressure caused byspurious main pressurizer spray initiation. The simulationresults showed that even if all the proportional heaters andback up heaters were quickly turned on and stayed on, itcould not prevent the safety injection signal from beinggenerated on low pressurizer pressure when thepressurizer main spray was spuriously turned on with100%, 50 %, or 25% of the full spray flow rate. Thepressurizer heaters could prevent the safety signalgeneration if the spurious main spray flow is 12.5 % of thefull spray flow rate. For MSO 36 scenario, (Spuriousopening of pressurizer main spray valve (one or bothvalves)) AND (Inability to trip, or spurious operation ofReactor Coolant Pumps (RCPs) will generate safetyinjection signal regardless of the success or failure of thepressurizer heaters, which should be treated as spurioussafety injection signal initiating event. Based on thisconclusion, the credit for the pressurizer heaters in MSO36 scenario was taken out in the reference plant fire PRA.