Examining the significance of CRUD source-term at the coolant contact interface during decommissioning

In Korea, Nuclear Power Plants continually prepare and revise the final safety analysis report (FSAR), which is essential for predicting the source-term information of radioactive materials throughout their lifecycle. This report provides detailed information on the source-terms of Chalk River Unidentified Deposits (CRUD). The management of radioactive corrosion products, present on nuclear fuel surfaces and within the primary system, is crucial for ensuring equipment integrity and controlling worker exposure during operation. Unlike earlier studies that focused solely on the radioactive inventory of major components, this study established an integrated evaluation framework by coupling the CRUDTRAN, ORIGEN2, and PHITS codes to quantitatively assess the relative contribution of the CRUD source-term on the core support barrel (CSB) to worker doses, in comparison with the activation source-terms of the reactor pressure vessel (RPV). By calculating these specific source-terms and conducting subsequent radiation exposure assessments, this work underscores the critical significance of the CRUD source-term during the decommissioning phase. The comparative dose assessment revealed that in the absence of system decontamination, the radiation exposure contributed by the CRUD source-term exceeded that from the structural activation of the RPV across the range of deposition-fraction assumptions, from about 1.5 times under the minimum assumption to about 117 times under the maximum assumption. These quantitative findings indicate that CRUD is a major source of worker exposure during the decommissioning phase, which should not be neglected relative to the activation of internal components.