Structural integrity assessment of pressure tubes for Wolsong Unit 1 based on operational experiences

Abstract Pressure tube integrity has been considered as a key issue since the first operation of the CANDU reactor. Wolsong Unit 1 has been in service since 1983 and subjected to inspections three times covering 44 tubes. The in-service inspections revealed that a major portion of inspected tubes was in contact with calandria tubes. This is likely to increase the probability of blister formation which is a potential threat to pressure tube integrity. Fortunately, the inspection results indicated that no tube has been affected by blister formation so far. Nevertheless, to reduce the undue risk of blister formation the utility has decided to conduct spacer relocation every year until the entire core is covered. On the other hand, LBB analysis of pressure tubes using AGS performance measured at Wolsong Unit 2 indicated that the operational safety margin was marginal when using 15-year operational data. This raises the concern of pressure tube integrity at Wolsong Unit 1 which has a more than 15-year operation. This paper presents the overall integrity evaluation of Wolsong Unit 1 pressure tubes considering AGS performance test results and operating experience data.