원전해체 시 노심 배럴내 방사화부식생성물을 고려한 선량평가 및 최적제염 적용 연구

Abstract

A Study on the Dose Assessment Applying CRUD in the Core Support Barrel during Nuclear Power Plant Decommissioning and Optimal Decontamination Application Lee SangHeon Advisor : Prof. Song Jong Soon, Ph.D. Department of Nuclear Engineering, Graduate School of Chosun University Securing the full-cycle of the development of nuclear technology, including nuclear power plant construction, operation, and decommissioning, as well as radioactive waste management, is essential for the continuous development of nuclear power and is crucial in terms of ensuring continuity. As the source-term information of radioactive materials generated by nuclear power plants must be predicted or analyzed for the entire life cycle, nuclear power plants in South Korea are continuously preparing and revising the Final Safety Analysis Report (FSAR), which serves as the main data input for design. The FSAR covers how to secure radiation source-terms which are major material dependent input factors in shielding design, exposure dose assessment, and system management, and provides information on the source-terms information of Chalk River Unidentified Deposits (CRUD), which are radioactive corrosion products in the reactor coolant system. Radioactive wastes generated in the primary system of nuclear power plants are radioactivated by neutrons during operation, and the importance of managing these materials is very apparent in terms of radioactive waste management. In particular, the management of neutron induced radioactive corrosion products existing on the surface of nuclear fuel and inside the primary system is very important in terms of ensuring the soundness of the equipment during operation, water chemistry management, and worker exposure management during operation. For this purpose, radiation source-terms of the material generated in nuclear power plants are periodically evaluated and managed to ensure safety. Furthermore, research and development on the topics of worker exposure management measures during operation or considering the time of decommissioning is underway. This study can be differentiated from previous studies considering three aspects. First, previous studies on exposure dose assessment of dismantling workers were limited to considering the radioactive inventory of the major component. To improve on this, calculated the source-terms of CRUD in the core support barrel and the radiation source-terms of the material in the reactor pressure vessel to derive the results for a worker exposure dose assessment in the reactor core support barrel, including the CRUD source-terms considering the presence/absence of system decontamination at the time of decommissioning. For the full-cycle (34 cycles) operation of Kori Unit 1, the assessment shows that the source-term of CRUD in the core is 2.05E+12 Bq at the time of permanent shutdown and 8.17E+11 Bq at the time of decommissioning. In the radioactive assessment of the reactor pressure vessel, the result is 3.70E+11 Bq at the time of permanent shutdown and 1.48E+11 Bq at the time of decommissioning. Second, based on the derived source-terms, we used the Monte Carlo code to obtain exposure dose assessment results for the decommissioning workers of the nuclear power plant, including the CRUD in the core support barrel. The result due to the CRUD in the core at the expected decommissioning time is 2.37E-02 mSv/h, and the result due to the radiation of the reactor pressure vessel is 2.03E-04 mSv/h. Third, based on the exposure dose assessment including the CRUD in the core support barrel, various types of compounds that can exist in radioactive corrosion products were derived to emphasize the need for system decontamination before CRUD removal. The need for further research was emphasized.