Seasonal and contextual factors in level 3 PSA

There are several factors that - through their implications to nuclear accident consequences - may affect level 3 probabilistic safety assessment (PSA) results significantly. For example, now, ice cover and frost may affect the transport of radionuclides; an initiating event, such as tsunami or loss of external electric power, may cause the population to be evacuated before release or impede evacuation; extreme snow as an initiating event implies that the season inquestion is winter, and therefore winter weather should be used in atmospheric dispersion calculations. In this report, such factors are called seasonal and contextual factors (SCF). These factors are not systematically taken into account in level 3 modelling currently.Thisreport makes an overview of possible SCF’s and their potential impacts toaccident consequences and level 3 analysis. SCF’s are listed together withtheir implications. SCF’s affect many important level 3 phenomena such asaquatic dispersion, transport of radionuclides in the environment andbiosphere, population demography and behaviour, and attenuation of ionizingradiation. These, in turn, affect level 3 analyses concerning population dose,evacuation, sheltering and distribution of radionuclides in the environment.Waysof incorporating SCF’s in level 3 analyses are discussed. For example, theyaffect dose assessment parameters, use of weather data, and estimation ofcontaminated land area. Constructing a framework for incorporating SCF’s inlevel 3 analyses, in a manner similar to those widely used for external events, would make this incorporation easier.Systematic research is needed to find out which SCF’s are significantenough to merit incorporation in PSA, and how to incorporate them in areasonable manner. This will involvemultidisciplinary modelling, analysis and experimentation.