A study on the external dose-rate conversion factors for radionuclides in the infinite environmental media based on the ICRP 103 dosimetric setting

Abstract

The dose-rate conversion factors (DCFs) prescribed in FGR 12 and FGR13 of USEPA have been widely used for assessing public members and radiation workers’ doses due to radionuclides released to the environment from nuclear facilities under their normal operations or accidental conditions. Recently, the dosimetric models and parameters which include use of the Reference Male and Female Phantoms (ICRP 110, 2009), the revised tissue weighting factors and radiation weighting factors (ICRP 103, 2007), as well as the updated decay data of radionuclides (ICRP 107, 2008) have been significantly changed. All of these changes should affect the values of DCFs. Therefore, the data set of DCFs should be revised to reflect such recent changes. In this study, the DCFs for effective and equivalent doses were calculated for three exposure settings: air submersion (skyshine), ground surface contamination (groundshine) and water immersion. Doses to the Reference Phantoms were calculated by Monte Carlo simulations with the MCNPX 2.7.0 radiation transport code and DOSFACTOR-DOE. It is evident that radiations produced extremely far from the receptor phantoms do not contribute to the resulting dose, while they increase computation time and relative errors significantly. To avoid this inefficacy, appropriate converging of distances (CODs) is employed for this computation. In order to determine the CODs for photons having different energies, trial calculations were made with a simplified receptor model which is the tissue equivalent sphere of 1 m in diameter centered at 1.5 m above the ground surface or deep in water. The CODs were 2.5 ~ 6 MFPs depending on the photon energies in the cases of skyshine and groundshine, and about 7 MFPs in the case of water immersion, respectively. The MCNP transport calculations were tried out for the source volume and area within the converging of distances (CODs) practically contributing to the dose-rates, which had been determined by a simplified c...