OPR1000 발전소의 축방향출력편차 비정상에 대한 연구

Abstract

Much research has been conducted around the world since the first axial offset anomaly(AOA) phenomenon occurred in 1988. In June 2015, there was an axial offset anomaly in Korea. It caused a significant difference between the design axial shape index(ASI) and actual measured ASI. In the case of OPR1000, the difference between the design ASI value and the measured ASI value tends to increase little by little. Therefore, there is a sufficient risk that AOA may occur. So, it is necessary to evaluate and analyze the AOA risk of OPR1000 before the AOA occurs, and reduce the AOA risk. It is important to find the optimal zinc injection time to lower the AOA risk since some OPR1000 plants have plans to perform zinc injection during operation. Therefore, in this thesis, AOA risk assessment is performed to find the optimal zinc injection time to reduce the AOA risk in OPR1000 which is performing zinc injection. The optimum zinc injection time will be analyzed through AOA risk assessment in and fuel cycles. As a result of fuel cycle AOA risk assessment of OPR1000, it was evaluated that the maximum value of core boron mass did not exceed the limit value of AOA recommended by EPRI even after zinc injection after 50 EFPD at the beginning of the cycle, and it was found that the possibility of AOA was low. The results of AOA risk assessment showed that zinc injection was possible after 50 EFPD. Based on the zinc injection experiences of other plants, the best time of second zinc injection was conservatively evaluated as 100 EFPD after OPR1000 fuel cycle startup. Some OPR1000 plants plan to perform zinc injection during operation, and finding the optimal zinc injection time in the plants is a important problem. In this thesis, AOA risk assessment of and fuel cycles in OPR1000 was conducted to investigate the optimal zinc injection time to reduce AOA risk. Zinc injection in fuel cycle was found to be possible at the beginning of the cycle (50EFPD), unlike 200 EFPD in fuel cycle. This is the optimal zinc injection time for the economy and safety of the reactor and can be effectively used for zinc injection in OPR1000. This study showed that the second zinc injection can be performed at the beginning of the fuel cycle, which is a meaningful result. Since the deviation between the design ASI and the measured ASI is continuously increasing in OPR1000, careful monitoring is needed and zinc injection is required to be performed in accordance with the optimal time found by the AOA risk assessment.