Combining DCVD Measurements At Different Alignments For Enhanced Partial Defect Detection Performance

In the current Digital Cherenkov Viewing Device (DCVD) measurement methodology, the DCVD is aligned over the center of a fuel assembly when measuring emitted Cherenkov light. Due to the collimation of light, and due to the lifting handle of PWR fuel assemblies covering the fuel edges, the DCVD is more sensitive to partial defects near the fuel assembly center as compared to the periphery. Here, we investigate the sensitivity of the DCVD for detecting partial defects for various alignments. By performing measurements at both the center and near the assembly edges, the measurement methodology becomes more sensitive to rod substitution near the fuel edges.DCVD images were simulated for different partial defect scenarios with 30% of the fuel rods removed or replaced with low, medium or high-density rods. Simulations were run with different DCVD alignments during a measurement, and the Cherenkov light distribution in the images were analyzed and compared to simulated images for a fuel assembly without defects. The simulation results were also compared with measurements of intact spent fuel assemblies.The work presents results for different measurement and analysis methodologies, to suggest a methodology that minimizes the number of measurements and alignments, while obtaining more detailed, quantitative information about the Cherenkov light emissions. Different quantitative analysis methods are evaluated for the different measurement strategies, to investigate the DCVD capability of detecting various partial defects using the optimized methodology.