[1B06-09] Decommissioning Evaluation Methods

[1B08] Development of Risk Assessment Methodology for Nuclear Power Plants in Decommissioning Phase

(1) Overview of Risk Assessment and Selection of Initiating Events

*Taro Shimada¹, Tsuyoshi Sasagawa¹, Kazuji Miwa¹, Shizuka Takai¹, Seiji Takeda¹ (1. JAEA)

Keywords:decommissioning, risk assessment, radiation exposure risk, dismantling activity, initiating event, event tree

It is necessary to develop the methodology for risk assessment during decommissioning so as to select the components or tasks based on the risk-informed at the nuclear regulation inspection. The characteristic is that the radioactive contamination that may be released in the event of an accident fluctuates spatially and temporally as the dismantling work progresses. We have started to construct a methodology for the risk assessment in decommissioning phase. And an outline of risk assessment based on the characteristics of the dismantling work was created. The risk is defined as the product of exposure dose and frequency in this study. As a result of investigating cases of decommissioning and similar trouble events during periodic inspection work, many cases related to fire during cutting work at dismantling were found. Based on the results, quality engineering methods such as FMEA (Failure Mode and Effects Analysis) were used to select the initiating events due to human error. In addition, event trees were created assuming that the events progress due to the failure of mitigation measures for those initiating events.