Design optimization with performance quantification of scintillator-based partial defect detector

Abstract

The International Atomic Energy Agency, IAEA requests several nuclear safeguards for the nuclear non-proliferation and the prevention of diversion of nuclear materials. As a kind of safeguard, the quantity of spent nuclear fuel is verified before it goes to be ‘difficult-to-access’ or be disposed permanently. The criterion of quantity verification is half amount of fuel rods in a fuel assembly. In the case of South Korea, the quantity verification of spent nuclear fuel is carried out every year on a regular and irregular basis. This research analyzes the detection capability of a scintillator-based partial defect detector(SPDD) which is one of the NDA detectors for the quantity verification of spent nuclear fuel. The maximum performance of the entire SPDD system and the single detector unit is quantified as the minimum detectable number of dummy rods. It is utilized as a performance criterion to confirm whether it is varied after the design optimization. SPDD is inserted into the guide tubes to receive the gamma dose from the spent fuel and it makes the performance vary with the different distribution of guide tubes. Two different design optimizations are performed to solve a limitation of the previous conceptual design of SPDD. The radial distribution of SPDD system is optimized with deploying additional detector legs in the gap between the spent fuel rack and the fuel assembly. It shows better performance than the previous design for the fuel rods located at the edge of a fuel assembly. The variation of detection capability is also analyzed with different axial height of the SPDD in the guide tube. The SPDD located above the spent fuel assembly can also identify a same amount of the minimum detectable number of dummy rods which is the maximum performance of SPDD located at the center. Therefore, the variation of the detection capability of SPDD with different types of fuel assembly can be minimized through these design optimizations. Also, it is shown that, through the performance quantification, the SPDD has a constant performance with different operation history of a spent fuel.