Assessment of occupational radiation exposure from gamma-emitting rad ionuclides in the bio-shield of Kori Unit 1 during decommissioning

Abstract

Abstract

The external dose to the workers of bio-shield of the Kori Unit 1 was evaluated by using the VISIPLAN 4.0 code to secure the radiation safety of its decommissioning work. In particular, radionuclide-specific activity concentration data, derived from prior MCNP simulations, were used to model three-dimensional radiation work scenarios. Each scenario was simulated with shielding and sampling configurations to calculate the external dose rates. Worker operation times were estimated based on the ICRP-recommendation and Nuclear Safety Act of annual average dose limit of 20 mSv. Variations in worker role, position, and task duration resulted in substantial disparities in individual cumulative doses. The maximum dose rate in scenario 1 under the 8-year cooling condition was 2.3 × 10 −1 mSv/h at 3 m height, decreasing to 9.3 × 10 −2 mSv/h under the 15-year condition (∼60 % reduction). A 20 mm lead shield reduced the dose rate by ∼86 %. The total dose rate in scenario 2 under the 8 year cooling condition was 1.33 × 10 1 mSv of workers 1 and 2, ∼22 times that of Worker 3. The minimum required shielding thickness was estimated at 14.8 mm. The allowable number of complete sampling operations was 32 and 80 for the 8 and 15 year cooling conditions, respectively.