Simulation study of muon tomography for enhancing the nuclear security of transportable microreactors

Enhancing the nuclear security of containerized transportable nuclear reactors, particularly microreactors, presents significant challenges, as conventional inspection techniques—such as gamma spectroscopy, neutron scanning, and X-ray imaging—struggle with shielding penetration high operational costs, and spatial resolution. This study investigates the application of cosmic-ray muon scattering tomography as a non-invasive imaging method to enhance the security of microreactors housed in transportable freight containers. Monte Carlo simulations were conducted using the Geant4 software platform to model muon flux at sea level, while a representative microreactor geometry with multilayer shielding was developed and analyzed with detector arrays in both vertical and horizontal orientations. Internal features were reconstructed using the Point of Closest Approach (PoCA) method and phase space analysis, enabling the detection of dense nuclear materials. The results demonstrate that muon tomography can effectively reveal internal reactor structures and distinguish high-Z components even through substantial shielding, with imaging performance strongly influenced by detector configuration. These findings highlight muon tomography as a promising, non-intrusive method for enhancing the safeguarding and security of containerized nuclear microreactors during transport and storage, with detectors integrated directly on the container.