Multiple-scattering muography of a thick-walled spent-fuel cask: A high-statistics Geant4 simulation

Abstract

Multiple-scattering muography is a passive, non-destructive technique for assessing spent-fuel dry-storage casks. A key challenge is to quantify where and how muons interact inside such a cask, for instance, the CASTOR® V/19, and to translate those interactions into practical guidance for detector layout and reconstruction algorithms. A detailed Geant4 model of a fully loaded CASTOR V/19 cask with four ideal tracking planes was simulated with 50×106 atmospheric-muon tracks. Three analysis observables were defined: Total material crossings Nhit, hard-scatter count Nint, and the integrated root mean square (rms) scattering angle Δθrms. These metrics build an interaction taxonomy allowing to connect muon tracks to detector and algorithm requirements. We find that of the incident muons, 36% traversed the shielding, yielding 18.4×106 reconstructed trajectories. Each transmitted track intersected on average 15.5 (±9.4) fuel rods and 2.2 (±1.1) fuel assemblies, generating more than 11×107 fuel-rod crossings for statistical analysis. Bottom-exiting tracks, ≈87% of which interacted with fuel, carried the highest information content. The interaction taxonomy links regimes of Nint to a reconstruction algorithm choice, and it informs detector placement. These results provide a quantitative baseline for optimizing detector geometry and reconstruction strategy in CASTOR V/19 muography.