Radiological safety assessment for transportation of reactor pressure vessel during decommissioning of a nuclear power plant in Korea.

In Korea, decommissioning of nuclear power plants and transportation of the decommissioning waste are expected to expand in the near future. It is necessary to confirm that radiological risks to the public and workers are not significant through radiological safety assessment. The objective of this study is to assess the radiological safety for transportation of RPV waste, which is a major decommissioning waste with relatively high level of radioactivity. It was assumed that the waste would be transported to the Gyeongju disposal facility by land transportation. First, the source term and transportation method of the RPV waste were determined, and the external dose rates from the waste were calculated using MCNP. Then, transportation scenarios were assumed under both normal and accident conditions. Under the scenarios, radiation doses were calculated using the RADTRAN. Under normal operation scenarios without a transportation accident, assuming 40 shipments per year, the average individual doses for the public ranged from 6.56×10-6to 2.18×10-2mSv yr-1. The maximum individual doses for only a single shipment ranged from 2.43×10-6to 3.14×10-1mSv. For cargo handlers and vehicle crew members, the average doses were 2.26×101mSv yr-1and 2.95 mSv yr-1, respectively. Under transportation accident scenarios, average individual radiological risks which are product of the radiation doses and the annual accident rates ranged from 1.14×10-11to 1.61×10-10mSv yr-1by transportation route segment when considering the transportation accident rate. Average individual doses assuming transportation accident occurrence ranged from 2.62×10-4to 1.42×10-3mSv. The maximum individual dose under accident conditions was 7.99×10-2mSv. The calculated doses were below the regulatory limits in Korea. However, relatively high doses were observed for cargo handlers and vehicle crew members because of conservative assumptions. This study results can be used as basic data for the radiological safety assessment for the decommissioning waste transportation in the future.

Derivation of dose constraint for the general public around nuclear power plants with operational data of radioactive effluent releases.

For radiation protection optimization, ICRP proposed dose constraint as quantitative value for planned exposure situation based on representative person concept. The objective of this study is to derive dose constraints for the general public around nuclear power plants in Korea by applying representative person concept. The dose constraints for the general public around NPPs were derived through a total of six steps. The steps consisted of setting source terms, setting exposure pathways and scenarios, setting candidate groups for a critical group decision, setting habit data, calculating radiation doses, and proposing dose constraints. Through these steps, the radiation dose distribution of the general public around the NPPs was obtained, and dose constraints were proposed using the dose distribution. Radiation doses to the general public around all the Korea NPP sites ranged 1.63 × 10-2 to 1.32 × 10-1 mSv/y. Using the dose distribution, 0.15 mSv/y, 0.10 mSv/y, and 0.08 mSv/y were proposed as dose constraints. The dose constraint values derived in this study are proposals. Therefore, it is judged that the dose constraints should need furthermore discussion with regulators, licensees, and radiation protection experts considering societal and economic factors for radiation protection. The proposal for dose constraints developed in this study can be used to optimize radiation protection for the general public around the NPPs.