Kori Unit 1, the first commercial nuclear power plant (NPP) in Korea, was permanently shut down in 2017 and was scheduled for decommissioning. Various programs must be planned early in the decommissioning process to safely decommission NPPs. Radiological characterization is a key program in decommissioning and should be a high priority. Radiological characterization involves determining the decommissioning technology to be applied to a nuclear facility by identifying the radiation sources and radioactive contaminants present within the facility and assessing the extent and nature of the radioactive contaminants to be removed from the facility. This study introduces the regulatory requirements, procedures, and implementation methods for radiological characterization and proposes a methodology to link the results of radiological characterizations for each stage. To link radiological characteristics, this study proposes to conduct radiological characterization in the decommissioning phase to verify the results of radiological characterization in the transitional phase of decommissioning NPPs. This enables significantly reducing the scope and content of radiological characterization that must be performed in the decommissioning phase and maintaining the connection with the previous phase.

The chelating agent and cellulose generated during the operating and decommissioning of a NPP’s form organic complexing compounds. That is accelerate the migration of radionuclide and have a bad influence of LILW disposal site. In this study, the GoldSim (RT module) program was used for the effects of radionuclide migration by organic complex compounds as described above. A scenario was derived for evaluation, and a conceptual design (Concept Art) of the GoldSim model was performed. 1) Derivation of the scenario. For the scenario, we selected a groundwater flow scenario in which groundwater flows in and radionuclides flow out after a lapse of time after the operation of the LILW disposal site in Gyeongju is closed. The inflowing groundwater comes into contact with radioactive waste and the radionuclides dissolve. The dissolved nuclides move past the drum and out of the disposal vessel due to the advection phenomenon. Radionuclides spilled from the disposal vessel pass through the silo internal filler (crushed stone) and reach the engineering barrier concrete. Radionuclides from degraded concrete are scenarios that move along the flow of groundwater to the near and far. 2) Radionuclide migration concept design. The radionuclide movement section was largely designed with Inner (Inside the silo), Near and Far. (A) Inner (Inside the silo) This section is where radionuclides move from the radiation source to the engineering barrier (silo). The detailed migration path was designed to allow radioactive nuclides to flow out and move to waste drums, solidified matrix of indrum, disposal vessel fillers, disposal vessels, silo fillers (crushed stones), and engineered barriers (concrete). The LILW disposal site in Gyeongju has a total of 6 silos. Each of the 6 silos was modeled and designed in consideration of the structural information and positional impact. (B) Near & Far. In generally design, the near is form source term to engineered barrier and far is beyond the engineered barrier. In this study, the near and far designed by radionuclide in the section from the beyond the engineering barrier (silo) to the sea through the groundwater flow through the natural rock. Especially in the case of near, the design was made by applying the position of the natural rock sampling drill hole.