A New Approach to Selection of Inspection Items using Risk Insight of Probabilistic Safety Assessment for Nuclear Power Plants

Abstract

The regulatory periodic inspection program (PSI) conducted at every overhaul period is the most important process for confirming the safety of nuclear power plants. The PSI for operating nuclear power plants in Korea mainly consist of component level performance check that had been developed based on deterministic approach putting the same degree of importance to all the inspection items. This inspection methodology is likely to be effective for preoperational inspection. However, once the plant is put into service, the PSI must be focused on whether to minimize the risk of accident using defense-in-depth concept and risk insight. The incorporation of defense-in-depth concept and risk insight into the deterministic based safety inspection has not been well studied so far. In this study, two track approaches are proposed to make sure that core damage be avoided: one is to secure success path and the other to block the failure path in a specific event tree of PSA. The investigation shows how to select safety important components and how to set up inspection group to ensure that core damage would not occur for a given initiating event, which results in strengthening defense-in-depth level 3.

Fig. 1 Flow chart for defense in depth(3)

Fig. 2 Framework of reactor oversight program(4)

Fig. 3 Relationship between PSA and DID(7)

Fig. 4 Relationship between level 1-3 PSA and DID level 1-5

Fig. 5 Evaluation of the event tree for station blackout initiating event

Fig. 6 Determination of success criteria for AFT heading

Fig. 7 Inspection items selected for AFT heading

Fig. 8 Basic event list obtained from PSA cut set evaluation

Fig. 9 Inspection items obtained from minimal cut set evaluation for AFT

Table 1 Items subject to regulatory inspection of domestic nuclear power plants