Kori 1, the first commercial reactor in Korea, was permanently shut down in 2017 and is preparing for decommissioning in the mid-2020s. Although Kori 1 is shut down, some radiation sources remain in the system; as such, the dismantling workers are exposed to radiation until decommissioning is completed. Unexpected radiation events have been reported in some decommissioning nuclear power plants (NPPs), which resulted in additional radiation exposure to workers and significant financial losses due to delays in the decommissioning schedule. Hence, an appropriate radiation protection program must be established to minimize radiation exposure as well as the economic burden. In this study, radiation doses from precedent decommissioning NPPs worldwide are compared with those estimated from Kori 1 to determine dose reduction measures that can achieve radiation exposure as low as reasonably achievable to decommissioning workers.
Following the permanent shutdown of Kori Unit 1 in June 2017, the Republic of Korea has been preparing for full-scale decommissioning work. In addition, the design life of 12 units will expire by 2030. If decommissioning begins without initially extending the lifespan of nuclear reactors, massive amounts of decommissioning wastes will be generated in a short period. The total amount of radioactive wastes generated during the dismantling of a pressurized water reactor is estimated as 6200 tons, and approximately 70% of the total radioactive wastes are classified as metal wastes. Self-disposal through the decontamination of contaminated metals can contribute to the economic feasibility of decommissioning nuclear power plants because it can reduce the disposal cost of medium-and low-level radioactive wastes. Therefore, this study evaluated the possibility of self-disposal of steam generators that may occur during future decommissioning. The radioactivity analysis data on transferring the replaced steam generator of Hanul Unit 1 were used as the source term. The decontamination factor was calculated by applying 200 units from 1200 to 2000, and the radiation dose was evaluated using the RESRAD-RECYCLE code. Consequently, the single-nuclide concentration and sum of the allowable concentration fraction for mixed radionuclides at a decontamination factor of 1400 were below the regulatory requirements; however, the dose evaluation results exceeded the allowable dose in some scenarios. The decontamination factor was 2000, when the dose evaluation results for all scenarios met the regulatory requirements.
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