Exploring site risk for a Multi Unit SMR Site

The need to adequately account of unit interactions when conducting safety analysis of nuclear reactors was highlighted by the Fukushima disaster of 2011. Traditional PRA techniques considered each unit in isolation, which can lead to underestimation of risk when units can impact the safety of other units in accident scenarios. The need to implement multi-unit PRA will increase when SMRs become commercially operative, as it is expected that reactor units per site will exceed what is common today. This study developed a method for scaling site risk as the number of units per site increases, with particular focus on SMRs. A number of input parameters were selected depending on the nature of the site under investigation; an algorithm then projects from an input risk of unit in an m unit site, to the site risk of an n unit site, where n>m. It was found that even in the least conservative risk estimates, the site risk far exceeded linearly scaled risk metrics used by traditional analysis techniques. In addition, positive unit interactions were modelled whereby units were able to provide support to other units in accident scenarios.