[2G09-13] PRA Application

[2G13] Study on reliability evaluation of confinement function under the decommissioning of accident-damaged nuclear reactor

*Takayuki Aoki¹, Takuma Nozaki², Atsuo Ikeda², Takayuki Negishi², Takeshi Morita² (1. Tohoku University, 2. Nuclear Engineering and Services Company)

Keywords:accident-damaged reactor, nuclear decommissioning, safety function, confinement function, PRA

When decommissioning a nuclear power plant, even if it is an accident-damaged one, it is necessary to maintain the three basic safety functions of shutting down the reactor, cooling the reactor, and confining radioactive materials, just as in a normal one. In other words, even in accident-damaged ones such as Fukushima Daiichi Unit 1-3, it is necessary to prevent or control the additional release of radioactive materials to the outside by maintaining the three basic safety functions.
Due to the high radiation dose rate, it is extremely difficult to access inside the reactor building for investigation and repair, and a lot of time and effort would be required to complete the decommissioning safely. To mitigate this situation as much as possible, it is extremely important to adopt a strategic, efficient, and effective method using risk information.
In this paper, we focus on a confinement function of the negative pressure control system of the reactor building and PCV during fuel debris retrieval, evaluate its reliability using PRA, and discuss the safety management of nuclear decommissioning based on the evaluation results.