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Review of Current Inspection Methods and Research Trends for Applications of Nuclear Safeguards Inspection of Spent Nuclear Fuel
Dry storage cask facilities are considered for temporary storage of spent nuclear fuels before their final disposal. According to relevant domestic laws and regulations, the integrity and gross defects of the PWR spent fuel must be inspected before they are transferred to the dry cask from a wet storage pool of a nuclear power plant. To meet nuclear safeguards requirements for a spent fuel transportation, the KINAC has been working to develop a simple and convenient Non-destructive Testing (NDT) equipment to verify the integrity and gross defects of the spent fuel assembly. This study was conducted in two processes. The first stage is to review the current NDT techniques conducted in the nuclear fuel manufacturing process. During the manufacturing process, the Ultrasonic testing (UT) and Eddy Current Testing (ECT) technique are used for detecting the cracks or foreign materials in a cladding of a fresh fuel. During an over-haul period after an end of one fuel cycle, the sipping test of the spent fuel is performed for detecting the failed fuel assemblies. If it is determined through the sipping test whether any fuel assembly contains a failed fuel rod, the failed fuel rod of lots of fuel rods in the assembly is found out using the UT instrument. The ECT is used for detecting the internal defects and oxide layer thickness of a fuel cladding. Because the UT and ECT are the wellknown technique and has already been employing for the spent fuel inspection, we adopted the UT and ECT technique for development of a new instrument for nuclear safeguards verification. The second stage is to design the UT and ECT equipment in consideration of nuclear safeguards activities in the spent fuel pool. For nuclear safeguards inspection, irradiated fuel or non-fuel items are distinguished. Thus, verification equipment newly designed using the UT and ECT should detect not only a failed rod, but also a false tube, or a false rod, or a different material from a cladding. New probe and signal processing methods are developed to achieve these goals. The design of UT and ECT probes are preferentially carried out according to technical requirements – the probe thickness including a damper material should be less than 1.0 mm - and the study on analyzing signal distortion caused from material difference will be conducted for development of the safeguards inspection equipment. Detailed results of our study will be discussed in this conference.
