Human performance evaluation: The procedures of ultimate response guideline for nuclear power plants

• This study adopts SPAR-H to evaluate HEPs in the URG procedures.
• The involvement of URG procedures could reduce CDF significantly.
• Upgrading the training level of staff will enhance the reliability effectively.
• Aiding the plant manager in making URG decision will enhance the reliability.

In the nuclear accident which occurred in Japan on March 11, 2011, several units of Fukushima conventional BWR experienced a total loss of power and water supply triggered by a heavy earthquake and subsequent Tsunami which were outside design models. In the past, when an accident occurred, operators in nuclear power plants (NPP) followed emergency operating procedures (EOPs) or severe accident management guidance (SAMG). However, EOP and SAMG are symptom-based procedures to cope with severe transients and accidents, depending on real-time operational parameters. Ultimate response guidelines (URG), a plant specific interim remedy action plan, was developed to manage accidents caused by compound disasters which exceed design models. The URG guides the plant operators’ conduct of reactor depressurization, core cooling water injection, and containment venting. This study adopts NUREG/CR-6883 (Standardized Plant Analysis Risk Human Reliability Analysis, SPAR-H) to evaluate human error probabilities (HEPs) of action and diagnosis in the current URG procedures. We found the human reliability of URG procedures analyzed by SPAR-H is about 85% (depending on different decision makers). Upgrading the training level of staff or enhancing plant managers ability to decide whether to execute URG will enhance the human reliability of URG procedures.