A Study on the Evaluation of Radioactive Corrosion Product Behavior at PWR for Extended Fuel Cycle

Nowadays nuclear power plant operation practice shifts to extended fuel cycle such as from 12 month operating cycle to 18-24 month operating one. It is important to emphasize that the current trend to longer fuel cycles has complicated the dilemma of finding optimum pH range for the primary coolant chemistry. Typically, current 12-month fuel cycles start with no more than 1200 ppm boron concentration at the start of a cycle, so a maximum value of 2.2 ppm lithium is supplied to satisfy the pH = 6.9 requirement. The recent ICRP recommendation (ICRP publication No. 60) for the radiological protection requires more strict reduction of ORE in the nuclear power plant. The major sources of the radiation are generated by the neutron activation of the non-radioactive corrosion products, that is called CRUD (Chalk River Unidentified Deposit). To estimate the generation of CRUD at the extended fuel cycle, the COTRAN code used, which was developed to simulate the behavior of the radioactive corrosion product (CRUD) for Korean Nuclear Power Plant and was developed with double layer concept model and are differentiated as soluble and particulate CRUD. The results show that as the operating cycle duration is extended, the ratio of Co⁵⁸/Co⁶⁰ becomes smaller. Especially, activities of Co⁶⁰ and Co⁵⁸ shows similar trend compared to the measured activities of those at steam generator tube surface of Millstone Point 3 PWR