Assessing the Feasibility of Transportable Nuclear Reactors: A Radiological Risk Case Study

The feasibility of a truly transportable nuclear reactor presents significant radiological challenges that must be addressed to ensure compliance with regulatory limits and operational safety. This study evaluates the radiological constraints associated with the transportability of the Transportable Helium-cooled One-megawatt Reactor (THOR), focusing on neutron activation, shielding performance, and external radiation exposure. Using advanced radiation transport and activation modeling within the SCALE framework, a comprehensive analysis was conducted to quantify dose rates during operation, post-shutdown, and transport. A key aspect of this work involved assessing activation products in core materials, auxiliary components, and surrounding environments to determine their contribution to residual radiation. The Ground Radiological Overview Of Transportable-reactors (GROOT) framework was developed and applied to evaluate neutron-induced activation of ground materials, providing a scalable methodology for site decontamination assessments. Results indicate that while shielding effectively mitigates operational dose rates, post-shutdown activation remains a limiting factor for rapid relocation. Compliance with NRC 10 CFR 71.47 transport dose limits is achievable, though more detailed modeling would be required to ensure full confidence in shielding performance across varied operational scenarios. Ground activation was identified as a key concern for long-term site contamination, with results showing activation levels highly dependent on soil composition and trace elements. Wide-area activation modeling demonstrated that certain materials require extended decay periods before reaching regulatory decommissioning limits. The findings of this study establish a foundation for optimizing the deployment of mobile nuclear reactors while ensuring adherence to radiation protection standards. By advancing activation modeling techniques, refining shielding configurations, and improving transport logistics, this research supports the development of truly transportable nuclear power solutions for defense, emergency response, and remote energy applications.