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This paper provides a very simplified analysis of the risk arising from earthquake hazard on nuclear plant. The analysis captures the effect of the hazard being defined as an exceedance probability, rather than a point probability, per unit time. It also investigates the common cause nature of the hazard to multiple lines of protection and illustrates the dramatic effect this feature can exert on plant risk. One of the principal findings from the analysis is that the potential for plant failure due to earthquake hazard is most likely between the design basis value and twice this value, if the design basis represents a 1% conditional probability of plant failure. This highlights the importance of analysing the beyond design basis response of nuclear plant.

This analysis is presented as part of a discussion of the changes made recently to the Office for Nuclear Regulation’s (ONR’s) Safety Assessment Principles (SAPs). These changes were prompted by lessons arising from the Fukushima event in March 2011 and include an extended discussion of beyond design basis response.

Tags: Reliability  
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