A New Method to Human Reliability Analysis for Seismic Events

There is increasing interest in advancing the state of art of conducting a probabilistic safety assessment (PSA) for seismic events especially in the wake of the Fukushima accident. One of the most dominant factors affecting the operational risk of nuclear power plants is human errors among other things. The new method discussed in this paper is concomitant with the EPRI's 2016 approach. The new method discussed above was applied to an operator action for early feed and bleed operation. The HEP evaluated in the internal events PSA for this operator action is 2.13E-2. This HEP was obtained by K-HRA using the time margin of 46 min, which was calculated as follows: (a) system time window=50min; (b) time delay=1min; (c) cognition time=1min; (d) execution time=2min; and (e) time margin=50-1-1- 2=46min. As mentioned earlier, this time margin evaluated in the internal events HRA is used in the seismic HRA screening tree. The operator action for early feed and bleed is applied to general transients (GTRN) initiating event in the internal events PSA, and so, will be applied to seismic induced GTRN initiating event. The GTRN initiating event frequency assessed in the internal event PSA is 4.30E-4/yr. The GTRN initiating event frequency for each bin was evaluated in this study using PRASSE code as follows: (1) 2.88E-4/yr for Bin 1; (2) 1.34E-4/yr for Bin 2; (3) 6.88E-6/yr for Bin 3; and (4) 7.74E-9/yr for Bin 4. Table 2 shows the example quantification results of the seismic HEPs and the bin CDFs for the feed and bleed operator operation. The original CDF for the GTRN initiating event with the HEP of 2.13E-2 and the GTRN frequency of 4.30E-4/yr was 5.31E-9/yr. However, the new CDF for the GTRN initiating event with the four HEPs shown in Table 2 is assessed to be 1.07E-9/yr.