United States Nuclear Regulatory Commission - Protecting People and the Environment

Review of Findings for Human Performance Contribution to Risk in Operating Events (NUREG/CR-6753, INEEL/EXT-01-01166)

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Publication Information

Manuscript completed: August 2001
Date Published: March 2002

Prepared by:
David I. Gertman (Principal Investigator), Bruce P. Hallbert (Program Manager),
Mark W. Parrish, Martin B Sattision, Doug Brownson, James P. Tortorelli
Idaho National Engineering and Environmental Laboratory
P.O. Box 1625
Idaho Falls, Idaho 83415-3129

Eugene A. Trager, NRC Project Manager

Prepared for:
Division of Systems Analysis and Regulatory Effectiveness
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code E8238

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This report documents results of analyses of human performance and investigations into its contribution to risk in operating events at commercial nuclear power plants. The Oak Ridge National Laboratory (ORNL) Accident Sequence Precursor (ASP) Program and the U.S. Nuclear Regulatory Commission (NRC) Human Performance Events Database (HPED) were used to identify safety-significant events in which human performance significantly contributed to risk. Standardized Plant Analysis Risk (SPAR) plant models developed under NRC sponsorship at the Idaho National Engineering and Environmental Laboratory (INEEL) were run using the Systems Analysis Programs for Hands-on Integrated Reliability Evaluation (SAPHIRE) software to calculate the conditional core damage probabilities (CCDPs) for these events.

Forty-eight events described in licensee event reports and augmented inspection team reports were reviewed. Human performance did not play a role in 11 of the events, so they were excluded from the sample. The remaining 37 events were qualitatively analyzed. Twenty-three of these 37 events were also analyzed using Rev. 2QA or Rev. 3i SPAR models and methods. The other 14 events were excluded from the SPAR analyses because they involved operating modes or conditions outside the scope of the SPAR models.

The results showed that human performance contributed significantly to analyzed events. Two hundred and seventy human errors were identified in the events reviewed and multiple human errors were involved in every event. Latent errors (i.e., errors committed prior to the event whose effects are not discovered until an event occurs) were present four times more often than were active errors (i.e., those occurring during event response). The latent errors included failures to correct known problems and errors committed during design, maintenance, and operations activities. The results of this study indicate that multiple errors in events contribute to the probabilistic risk assessment (PRA) basic events present in SPAR models and that the underlying models of dependency in HRA may warrant further attention.

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