Evaluation of eye lens dose to workers in the steam generator at the Korean optimized power reactor 1000

Abstract

Based on recent epidemiological studies of radiation-induced cataracts, ICRP (2011) revised the dose limit to the eye lens to 20mSv/y. Maintenance of steam generators at nuclear power plants is one of the highest radiation-inducing tasks, with a non-uniform radiation field. This study aims to evaluate eye lens doses in the steam generator at a Korean OPR1000. The source term was characterized based on CRUD-specific activity and both the eye lens dose and organ dose were simulated using MCNP6 combined with the ICRP voxel phantom and the Hanyang University tetrahedral mesh phantom. The eye lens dose was determined to be 5.39E-02 (±3.81E-03) ~ 9.43E-02 (±8.17E-03) Sv/h with a negligible effect of beta particles. The MCNP simulated skin doses and effective doses were found to be respectively 0.95~1.76 and 0.81~1.21 times the simulated lens doses depending on the phantom angle. These ratios of skin and effective dose to the lens dose were found to be similar to the results of Behrens' study of a gamma dominant radiation field. In order to prevent overestimation of the lens dose and implement the ALARA philosophy, 123% of the effective dose was proposed for radiation protection purposes as a substitute for the lens dose. In addition, skin equivalent dose may be used conservatively for estimation of the lens equivalent dose. This is one of a first in-depth study on dose to the lens of the eye at nuclear power plants. If the ICRP118 is codified in Korea, the study results will be effectively utilized to evaluate the lens dose for SG maintenance workers and enhance their radiation safety at nuclear power plants. In the future the flexibility of the phantom should be enhanced to mimic real postures of workers in the SG and to take into consideration the shielding effect of eye blinking and the mask worn by workers in addition to more detailed description of the geometry of the SG and measurements of its energy spectrum.