Dose assessment in level 3 PRA: A review of recently used methods

The assessment of ionizing radiation dose to the general public resulting from a nuclear accident is a central part of level 3 probabilistic risk analysis. This report reviews dose assessment methods used recently either in major studies (the SOARCA study by the Nuclear Regulatory Council, and the Fukushima accident study by the United Nations Scientific Committee on the Effects of Atomic Radiation), or in modern level 3 PRA analysis codes (VALMA, SILAM, RODOS). After a brief introduction to dose assessment, the methods are introduced by study/code. The methods of the Finnish VALMA code relies on work done at VTT previously, and on international standards and guidelines. It takes into account cloudshine, groundshine, inhalation and ingestion. The dose assessment of SILAM handles the same pathways as VALMA, and also rests on guidelines of IAEA and others. The dose assessment of RODOS relies on simple methods, but is quite versatile. The dose assessment used in the SOARCA study is the one implemented in MACCS2, and reflects the American way of dose assessment analysis. The dose assessment used in the UNSCEAR study originates from Russia, considers cloudshine, grounshine and inhalation, and contains submodels for finding radiation intensity in free air, the effects of the locations of exposed people, the whereabouts of people as a function of time, and conversion of radiation intensity to absorbed doses. It turns out that there has been relatively little progress in dose assessment methods in the last 20 years. Some suggestions on future research on improving the accuracy and plausibility of dose assessments are made. These rely on utilizing developments in modelling, simulation and computation in the last decades.