Modeling of Human Error for a Seismic PSA

Abstract

This paper describes a model for human error probability (HEP) for seismic probabilistic safety assessments (PSAs) of nuclear power plants and its application. Considering the factors unique to seismic events such as level of seismic motion and stress to the operators, the authors adopted a model called a limited ramp model (LRM), where HEP is assumed to be the same as that for internal event PSAs for zero level of seismic motion, and then increases linearly with seismic level to a constant at a certain seismic level. This model was applied to estimate the effect of human error on core damage frequency (CDF). Here, operator actions in the accident sequences initiated by loss of offsite power were categorized into two groups, short term actions and medium/long term actions, and parameters of the LRM for the HEP for each action were determined from available information on shaking table tests and an existing human reliability analysis method. The results showed that the effect of human error on the CDF was not significant for this case and indicated that, the modeling approach presented here is useful for examining the importance of various operator actions in seismic events.

Estimating the response times of human operators working in the main control room of nuclear power plants based on the context of a seismic event – A case study

“…For example, Yokobayashi et al (2002) suggested that the HEP of a certain HFE to be accomplished within a short time period after the occurrence of an earthquake (i.e., a short-term HEP) is defined by 15 times of its HEP quantified without considering a seismic effect. In addition, they offered a hypothetical ramp model for a long-term HFE, which expresses the effect of a seismic intensity on the increase of an HEP (refer to Fig.…”

Experimental Study on Nuclear Power Plant Operators’ Performance during a Major Earthquake with Aftershocks

“…When major earthquakes occur, nuclear reactors generally shut down automatically. However, operators must possess steady judgment to handle the malfunctions and defects resulting from earthquakes and to safely bring the reactor to cold shutdown (Shibata and Takada 1995;Yokobayashi et al 2002). To prevent erroneous judgments that aggravate disaster situations, as happened previously at Three Mile Island (Jang et al 2016) and Chernobyl (Salge and Milling 2006), operators regularly train using training simulators to respond steadily and appropriately during major earthquakes.…”

“…Several studies have investigated the impact of earthquakes on operator performance by setting up a simple simulated operation panel on a shaking table (Shibata 1987; Kitada et al 1994;Park et al 2018; Kim et al 2019;Yokobayashi et al 2002). Shibata (1987) set up a cathode ray tube (CRT) and keyboard on a shaking table and conducted an experiment in which subjects typed in the letters appearing on the CRT during vibration.…”

“…Only a few studies have experimentally examined aftershocks' effects on operator performance. Contrastingly, a number of literatures highlight the effects of aftershocks (Human-Machine Systems Research Subcommittee in Atomic Energy Society of Japan et al 2015; IAEA 2015; Liu and Hwang 2014; Shibata and Takada 1995; The National Diet of Japan 2012; Yokobayashi et al 2002;Yamaguchi 2021). In addition, every accident investigation report on the Fukushima accident described the adverse effects of aftershocks and accompanying interruption of operations, as follows: "Recovery tasks were further interrupted as workers reacted to the intermittent and signi cant aftershocks and tsunami" (The National Diet of Japan 2012, p. 14); "Aftershock was still continuing, prompting evacuation each time, and preventing the preparation from progressing" (Yamaguchi 2021, p. 110); "Until 15:25, before the second tsunami wave hit, six aftershocks with a seismic intensity of 4 or more were recorded in succession.…”

Seismic Robustness Analysis of Nuclear Power Plants

“…In the ramp model presented by Yokobayashi et al (1998), the operator performance is modeled by a linear relationship between the seismic-induced HEP and the PGA until a maximum ground acceleration level L is reached.…”