Preliminary Source Term Assessment on Kori unit 1 Radioactive Bioshield for Decommissioning

Large amount of neutron irradiation on bioshield due to over 30 years of operation, caused high neutron activation on the structure leading to contamination by various radionuclides. Despite of this importance, lack of geometric and material as well as operation history caused little precedent research on source term modeling. From conservative point of modeling on the source term, it is possible to achieve prediction of the amount of the radioactive waste and classification of clearance boundary which leads to analyze recycling possibility and worker safety during the D&D project. The study mainly focused on modeling 3D geometry of the RPV (Reactor Pressure Vessel) and source term, neutron flux distribution and concentration of major targeted radioactive nuclides. The actual license release should be assessed based on whole radionuclide, however based on related foreign nuclear power plant cases, Co and Eu hold most effects on contamination. Since the clearance boundary depends on total amount of radioactive nuclide existed further adding of nuclide with using ORIGEN could be enhance the conservativism of the result.