Research on skin dose assessment methods after severe accidents in nuclear power plants

In the event of a severe accident at the nuclear power plant, the radioactive plume can cause external immersion exposure and deposition exposure to the skin. The predominant code utilized for estimating the emergency planning zone of the plume, namely the MELCOR Accident Consequence Code System (MACCS), employs excessively conservative assumptions regarding skin deposition dose. As a result, skin dose is hard to meet relevant regulatory requirements. This paper introduces a novel set of conversion factors for the calculation of skin deposition dose and also assesses the immersion skin dose. Furthermore, the analysis encompasses the contributions of various nuclide groups and the impact of meteorological conditions on skin dose levels. The findings reveal that the skin deposition dose is markedly greater than the immersion dose. Specifically, at a distance of 10 km downwind, the immersion external exposure dose is calculated to be 0.01 Sv, whereas the deposition doses calculated from the new conversion factors and MACCS are 0.97 Sv and 1.27 Sv, respectively. This also indicates that deposition dose derived from the new conversion factors is lower than that produced by MACCS. Among six representative release categories, the categories of CI, BP, and CFE exert a more substantial impact on skin dose. For immersion external exposure, it is crucial to consider the contributions from inert gases and iodine, while for deposition external exposure, the primary contributors are rare metals, iodine, and cerium isotopes. The study further indicates that under conditions of constant atmospheric stability, the skin dose initially decreases rapidly with increasing wind speed, followed by a gradual decline.