Assessment of Safety Effect Due to the Change of the Assumptions Related to ECCS for Safety Analysis of Wolsong Unit 1

In recent safety analysis of wolsong unit 1, the thermalhydraulic analysis was performed using the CATHENA code and some parts of assumptions and initial conditions applied in this thermalhydraulic analysis were set as limiting conditions for operation (LCOs) of wolsong unit 1. The temperature condition of high pressure-emergency core cooling water (HP ECC) among these LCOs is limited to 27.8℃ due to the assumption (30.0℃) applied in safety analysis, therefore the water temperature in the tank of HP ECC may exceed this limit condition in summer season as a result of the global warming phenomena. The assessment of safety effect due to the change of the assumptions for safety analysis of wolsong unit 1 as described in Table 1 was performed. As result, since the effect is very small and the all acceptance criteria for each accident are satisfied, the increase of the temperature limiting condition of HP ECC and the modification of the system response times related to ECCS is considered to be possible.