Title: Challenges and Safeguards for Pebble Bed Modular Reactors
Author: Ali Alkis, NATO Defense College
Abstract: High Temperature Reactors (HTRs) have been explored globally for their advanced capabilities, including high thermal efficiency, versatility in fuel use, and potential for cogeneration applications such as district heating and chemical processing. Among these, the Pebble Bed Modular Reactor (PBMR) represents a modern innovation, utilizing spherical TRISO fuel pebbles for continuous on-load refueling. This approach, while advantageous for operational efficiency and flexibility, poses significant challenges for nuclear security and proliferation resistance.
Unlike traditional light water reactors (LWRs), PBMRs function as bulk material facilities, where nuclear material is dispersed across fresh fuel bins, reactor cores, and spent fuel storage. This unique configuration complicates traditional safeguards, which are designed for item-based verification of discrete fuel assemblies. The continuous fuel circulation and the bulk nature of the material make it difficult to track and verify fissile material effectively, increasing the potential for diversion or misuse.
This paper evaluates the proliferation risks associated with PBMRs, particularly their compatibility with existing International Atomic Energy Agency (IAEA) safeguards frameworks. It highlights the limitations of current methodologies in addressing challenges like on-line refueling, spent fuel reprocessing, and the technical feasibility of recovering fissile material from irradiated TRISO fuel.
To address these challenges, the paper proposes a hybrid safeguards approach combining advanced containment and surveillance systems, fuel flow monitoring, and bulk material accountancy. Collaboration among the IAEA, reactor developers, and international safeguards organizations is emphasized as critical to ensuring that safeguards are integrated into the reactor design from the outset.
As PBMRs are increasingly marketed to developing countries, their proliferation resistance must be rigorously evaluated. This work underscores the importance of designing safeguards-by-design strategies to uphold nonproliferation norms while enabling the safe and responsible deployment of advanced nuclear technologies.
This study aims to provide a roadmap for adapting safeguards to next-generation reactor designs, ensuring that nuclear innovation proceeds without compromising global security.