Monte Carlo Simulation for Passive Gamma Ray Emission Tomography of Spent Fuel Dry Cask

Dry storage cask has become more of a semi-permanent solution rather than a temporary one for spent fuel, since the permanent storage solutions has proved elusive over recent decades. It was estimated that 4500 dry casks will be loaded until 2025. Due to the increased service life of casks and rapid growth of loaded casks, safety concerns about the integrity of internal structure are rising. No internal sensors were placed in the casks and these casks cannot be open for obvious reasons. Therefore, DOE has funded an integrated research project to solve the spent fuel cask internal structure-monitoring problem with nondestructive evaluation methods. Passive gamma ray emission tomography is attractive for addressing partial defect detection and verifying the integrity of the spent fuel assemblies in dry cask because it has the potential to image spatial distribution of the active material in the spent fuel assemblies and the relative locations of spent fuel assemblies in the dry cask. The major objective of this work is to design a passive gamma ray emission tomography system to detect single fuel assembly missing or replaced in dry cask. In this work, a Transnuclear 32 cask (TN-32) with 32 loaded spent fuel assemblies was reproduced with detailed into fuel rod level in MAVRIC (Monaco with Automated Variance Reduction using Importance Calculation) sequence of SCALE6.2.3. The full detection instrument including the tungsten alloy collimator block, gamma ray detector (HPGe) and the translate-rotate motor are designed in this work. The prior information of spent fuel assembly (e.g., assembly type, burn up, operation history, cooling time) is known, and all 32 spent fuel assemblies are identity. Simulated instrument response data were processed using a variety of tomographic-reconstruction methods (e.g., back projection, filter back projection), and image-processing method. The sensitivity test about the rotation step size and scanning time were performed in this work. This work might provide a solution for spent fuel assembly in dry cask integrity detection.