An Investigation of FLEX Implementation in Maanshan NPP by Using MAAP 5

Abstract

In the CASE of Fukushima Accident, the extended loss of AC power (ELAP) caused by a heavy earthquake and the following tsunami led to loss of core cooling and loss of normal access to the ultimate heat sink (LUHS); hence, Nuclear Energy Institute released, NEI-1206 [1], considering additional diverse and flexible mitigation strategies—FLEX—that will enhance defense-in-depth for beyond-design-basis events external events (BDBEEs). In light of WCAP-17601-P [2], it was evaluated plant Nuclear Steam Supply System (NSSS) response by using MAAP5 to investigate tolerated ability of core under ELAP condition to determine what strategies and equipment must be taken and to alleviate those conditions which inhibit the ability to successfully survive in such an event. In this study, MAAP5.0.3 was used to simulate BASE CASE and PLANT-SPECIFIC scenarios to investigate RCS tolerated ability under seal leakage and emergency core cooling system (ECCS) is not available under ELAP condition. The BASE CASE is using installed equipment, and the PLANT-SPECIFIC scenarios are adding external portable equipment in the primary and secondary side. Once implement the FLEX strategies and add the external portable equipment, the coping capability increases the level of safety under ELAP and LUHS accident.