Study of the radioactivity inventory deposited in the reactor coolant system during the decommissioning of Kori Unit 1

Abstract

The Kori Unit 1, a first nuclear power plant (NPP) in South Korea stopped operation permanently on June 18, 2017 after 40 years of operation. Before the main decommissioning activities begin, full-system chemical decontamination operation (FSCDO) of the primary systems is planned to secure the safety of workers and minimize the quantity of radioactive waste. In this study, the radioactive inventory at the time of decommissioning of Kori Unit 1 was investigated. The CRUDTRAN code was used to make predictions by using the actual operation and maintenance history and design data of Kori Unit 1. Regarding the steam generator (SG), the prediction results obtained using the CRUDTRAN code were 17–30% higher or more conservative than the direct measurement results obtained using survey meters. By applying the oxide layer removal ratio (OLRR; obtained through a chemical decontamination field test using the contaminated specimen) to the oxidation/deoxidation process during FSCDO, the removal rate of radioactive inventory could be predicted. As an actual decommissioning work proceeds, the detailed data of radioactive elements in RCS systems can be obtained through sampling and chemical analysis. Those data will be much valuable for both the operation and future decommissioning of current NPPs.