Access Time and Safety Benefit Analysis of Additional Temporary Water Injection Measures on Primary After the Fukushima

After the Fukushima nuclear accident, National Nuclear Safety Administration carried out plant inspection nuclear safety on the nuclear plant in operation and under construction, and put forward improvement requirements for each nuclear power plant according to the inspection results. One of the improvement actions was to add temporary water injection measures on the primary side. At present, all power plants have plant requested to add mobile pumps and related water supply pipelines and operating procedures. By summarizing the calculation cases of plant, which selected representative accident sequences for deterministic analysis in the past, this paper determines the effect of implementing temporary water injection measures in primary circuit on accident mitigation at different times, and the results can provide time suggestions for the preparation of mobile equipment in plant. At the same time, the safety benefits after implementing temporary water injection measures in primary circuit in plant are analyzed by using probability analysis method. Based on the analysis of deterministic and probability theory, and considering the preparation time of accessing mobile equipments, it is considered that 4 hours is a reasonable access time for mobile equipments under SBO accident conditions. In the actual access process, this time can ensure that operators have a more suitable time to complete the preparation work of mobile equipments in operation, and at the same time contribute to the reduction of large release frequency. At the same time, it should be noted that at present, the contribution of implementing temporary water injection measures on the primary side under SBO accident is mainly analyzed. In fact, some accident situations with slow development except SBO accident also have great access possibility, so the actual safety benefits of temporary water injection measures on the primary circuit may be more.