Identification of Gas Accumulation Susceptibility in NPP’s Safety Related Systems and Operability Evaluation due to Gas Transportation

Instances of gas accumulation in the subject systems have occurred since the beginning of commercial nuclear power plant operation. NRC Generic Letter 2008-01, “requests that each licensee evaluate its ECCS, DHR system, and Containment Spray system licensing basis, design, testing and corrective actions to ensure that gas accumulation is maintained less than the amount that challenges operability of these systems, and that appropriate action is taken when conditions adverse to quality are identified.” All of the three NPPs have accomplished this evaluation and propose some corrective measures like revision of the operation procedures, installing the venting valves etc. Taipower also committed AEC to establish the acceptable quantity of the gas accumulation and continue to follow the development of gas transport methodologies in the industry. According to the NRC NRR Action Plan TAC.NO. ME3939 GAS MANAGEMENT (March 2011), other safety related systems, in additional to the systems covered by GL 2008-01, also have the gas accumulation issue and therefore must be concerned. This project will develop the numerical evaluation process with two phase flow software to simulate the gas accumulation and the transportation phenomena for the GL 2008-01 systems and validate the results by experimental analysis.