Ultimate response guideline strategy evaluation for Maanshan power plant

Abstract

Abstract After Fukushima accident, Taiwan Power Company has developed the Ultimate Response Guideline (URG) against the similar accidents. Two stages provision is used to depressurize the steam generators, named controlled depressurization and emergency depressurization. The URG for the Maanshan power plant is evaluated in this study. It is found that, under the technical specification requirement for reactor coolant system temperature decrease rate 37.8 °C/h, the power operated relief valve flow capacity cannot depressurize SGs to 1.57 MPa in one hour after earthquake. Sensitivity study shows, the time difference between reducing steam generators' pressure from 1.57 and 3.53 MPa to 0.69 MPa is less than during emergency depressurization. So, the target pressure of controlled depressurization can be set as high as 3.53 MPa. In case the raw water cannot be ready in one hour, the emergency depressurization action will be delayed and so does water injection. The minimum required raw water flow rate varies with injection time. A method is proposed to estimate minimum required flow under such condition.