Probabilistic Risk Analysis of Falsification Cases in the Japanese Nuclear Industry

Report Date: August 2002
Appendices: No

Abstract

Major falsification cases in the Japanese nuclear industry are analyzed using probabilistic risk analysis (PRA) methods. The mechanism through which falsification affects total system failure is modeled, the frequency of each basic event is evaluated including uncertainties and then fault trees are constructed in order to calculate the risk significance of each event. We also analyze how additions to existing regulations could contribute to risk mitigation or risk reduction, and we suggest methods for reduction of falsification-associated risks.

Consequently, the risk importance of basic events calculated for each case indicates that individual falsification has a large effect on each top event. Based upon the calculation results, we confirm that Japanese nuclear regulations, which were recently modified to strengthen the checking system of organization’s management and of the QA systems, can be valuable in reducing risk contributions from the failure of QA systems and faulty organizational behavior. We also suggest that Japanese regulatory bodies should encourage organizations to take measures, which would include the reviewing and improving of human resource allocation, the working environment, internal communications and education programs, in order to mitigate the risk of individual falsification.

Program:     NSP Nuclear Systems Enhanced Performance

Type:     TR 

RPT. No.: 13