Proceedings of the

The 33rd European Safety and Reliability Conference (ESREL 2023)
3 – 8 September 2023, Southampton, UK

Estimating the Performance Time of FLEX Implementation Based on Staffing Level Considering Multi-Unit Accidents

Yochan Kima, Jaewhan Kimb, Jinkyun Parkc, Sung Min Shind and Jong Woo Parke

Risk Assessment Research Team, Korea Atomic Energy Research Institute, Republic of Korea.


After the Fukushima Daiichi accident, many nuclear power plants have been developing plans for Diverse and Flexible Coping Strategies (FLEX) and preparing portable FLEX equipment to enhance defence-in-depth against beyond-design-basis events. To understand the feasibility and usefulness of the actions related to the use of the portable equipment, attempts have been made to apply human reliability analysis (HRA) methods to the estimation of the failure probabilities of the FLEX implementation actions. In this study, based on the characteristics of multi-unit accidents requiring FLEX actions, we propose to analyse the failure probability due to time insufficiency based on the association between human performance time and staffing level in a given scenario. A mathematical formula is developed for estimating the human performance time for portable equipment use based on staffing levels. Empirical data obtained from a firefighting experiment are then analysed for estimating a key parameter in the equation. Regarding the time-based failure probability, some important issues such as the expected distribution of FLEX actions, key values for calculating the time required, and the initial time of FLEX implementation are also discussed.

Keywords: Human reliability analysis, Diverse and Flexible Coping Strategies (FLEX), Multi-unit accident, Human performance time, Nuclear power plant, Firefighter response time.

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