Physics informed muon scattering tomography with momentum integration for nonintrusive monitoring of microreactor cores

Next-generation microreactors enable remote deployment and semi-autonomous operation, but compact, sealed, heterogeneous cores limit conventional safeguard approaches that rely on access and bulk accountancy. Limited inspection access and complex internal geometry reduce sensitivity to localized anomalies such as missing fuel. Here we demonstrate missing-fuel detection in microreactor scale geometries using muon scattering tomography under realistic cosmic-ray conditions. We introduce μ TRec, a physics-informed framework that reconstructs event-level curved muon trajectories by combining a Gaussian multiple Coulomb scattering model with Bayesian updating, then maps scattering density through voxel wise M-values for core integrity verification. We evaluate a representative hexagonal core containing 61 fuel flakes with embedded control drums and shutdown rods, using both idealized 5 GeV muons and zenith-angle-dependent 0-60 GeV cosmic-ray spectra. A single missing fuel flake is detected with 3× 10⁶ muons at 50 mm voxel resolution. Incorporating per-muon momentum further improves detectability, with gains of up to 2.4 times for laser-driven sources and 2.3 times for cosmic-ray sources relative to momentum-agnostic reconstruction. The method remains robust under practical detector limitations, showing only an 8.88% reduction in detectability for 10 mm spatial resolution combined with 10% energy resolution. Compared with PoCA, μ TRec achieves up to 4.8 times higher detectability at equal muon counts, supporting faster and more reliable defect identification.