CONTAINMENT AND SURVEILLANCE AS A PRIMARY APPROACH FOR SAFEGUARDING GEOLOGICAL REPOSITORIES

The disposal of spent nuclear fuel in geological repositories presents an entirely new challenge for international nuclear safeguards, defying conventional safeguards approaches for other stages of the nuclear fuel cycle. Nuclear material accountancy (NMA), the primary mechanism by which safeguards are applied to detect and deter diversion for non-peaceful use, cannot apply to nuclear materials permanently removed from the active fuel cycle via disposal. Long-term safeguards for repositories fundamentally require containment and surveillance (C/S), and only C/S. We propose that a repository be designated a Material Disposal Area (MDA), which is distinct from a material balance area (MBA), as there is no “balancing” or verifying NMA for materials in an MDA. In handing off nuclear material from NMA-dependent safeguards, as applied to the active fuel cycle, to C/S-dependent safeguards, as applied to the MDA, the concept of a Transition is introduced. Transition begins after the last materials accountancy measurement, a partial defect verification (PDV), conducted before spent-fuel assemblies are encapsulated in disposal canisters. Transition ends when disposal canisters enter the repository MDA. During Transition, nuclear materials exist only as items, and safeguards assurance is primarily a matter of maintaining continuity of knowledge (CoK) on items and confirming their receipt and integrity at the repository MDA. During Transition, NMA is complementary to C/S, invoked only if CoK is lost and the suspect item does not enter the MDA and must be re-verified or returned. Once items have entered the MDA detailed NMA information is no longer needed for safeguards purposes.