Development of the implementation standard for internal fire probabilistic risk assessment of nuclear power plants

Simultaneous multiple components failures (SMCF) of many safety significant components can lead to severe accidents, such as core damage and containment failure, and one of the most important factors causing SMCF is fire. Fire PRA is an analysis method which can quantitatively evaluate plant damage states, including core damage frequency. Because Fire PRA results can be used for identifying the causes of end states, such as SMCF of safety significant components induced by the effect of fire, by analyzing the results systematically, it is utilized worldwide. Considering the circumstances, the Atomic Energy Society of Japan (AESJ) has been working on the development of the "Implementation Standard for Internal Fire Probabilistic Risk Assessment of Nuclear Power Plants" since fiscal year 2012. This standard prescribes the requirements and specific methods to implement Level 1 PRA for accidents initiated by internal fire at NPPs during power operation, and focuses on the fire induced by internal causes, such as failure of components (ex. fire of electrical panels) and human errors during maintenance activities at NPPs while excluding external causes, such as earthquake and tsunami. This standard is being discussed at the Fire PRA subcommittee under the Risk Technical Committee for the Standards Committee of AESJ, and is expected to be published in fiscal year 2014. This standard will give great support to PRA engineers for performing the internal fire PRA with adequate quality, identifying vulnerability concerning internal fire moreover will contribute to further improvement of the NPPs' safety.