Speakers
Description
Resolving the internal geometry of a thick-walled spent nuclear fuel cask in detail is a demanding task in the field of muography. In thick-walled, heterogeneous systems, the multiple-scattering nature of cosmic muons complicates both trajectory reconstruction and the exact localization of where the dominant scattering occurred as the measured net deflection represents an integral over many material transitions and scattering events. This becomes particularly relevant when the object of interest shifts from coarse anomalies, e.g. fuel assemblies, to finer cask features as individual fuel rods, polyethylene rods or features located in the cask center. Analyzing the trajectories within the cask in high detail provides a first valuable information map, showing that detector positioning can improve the material information measured particles are providing. The measured muon flux an be narrowed to particles with specific information on material scattering or comparatively isolated trajectories with few material transitions.
This study uses theoretical interaction statistics within a CASTOR$^{\circledR}$ V/19 to derive strategies for positioning detectors that are tailored to specific applications in interim storage facilities. A series of representative measurement geometries are evaluated: varying the arrangement, vertical height, active area of the detectors, and the number of detectors.
For each configuration performance-related factors are evaluated, e.g., the expected exposure time needed for the muon statistics, usable muon flux under acceptance constraints, feasibility of use in high-security environments, and implications for suitable reconstruction algorithms.
Several use cases relevant to interim storage are addressed. From a safeguards perspective, the re-verification of cask-contents to provide a continuity of knowledge, such as empty fuel assembly slots or discriminating fuel assemblies form non-fuel bearing dummy elements to provide is looked into.
Other aspects include the analysis of deviations in the polyethylene moderator rods and changes in the local positioning of the fuel rods. In addition, scenarios such as fuel leakage leading to an accumulation of fuel on the cask bottom are being investigated. These scenarios lead to scattering anomalies, but require detector geometries that preferably measure only muons in the lower part of the cask to avoid a high level of integral scattering information one muon is carrying.
The results show that the placement of detectors can be optimized if the setup is adapted to the structure of interest: Smaller detectors with an additional upper layer may be sufficient for localized investigations in the lower region (e.g., a leaking fuel cone), while configurations near the upper edge efficiently investigate deviations of the moderator rods. Overall, the work provides a requirements-oriented framework that links detector positioning with specific measurement scenarios, covering exposure times, and reconstruction approaches for muography within the context of interim storage of nuclear waste.