Status of NDA Techniques in use for IAEA Verification of Light Water Reactor Spent Fuel

Under comprehensive safeguards agreements, States are obliged to declare the uranium and plutonium content of spent LWR fuel. In practice, this data may realistically only be calculated by employing specialised computer codes using the initial fuel composition and operating records of reactors. Declaration records and reports are formulated for each spent fuel item. On a routine basis, IAEA verification entails confirming the presence of declared items in the spent fuel storage by means of continuous containment and surveillance measures, or approved nondestructive verification methods supporting attribute tests. Under special circumstances, such as the loss of continuity of knowledge during periods when the core is open or when spent fuel is transferred to dry storage, the IAEA uses stronger verification methods supporting the independent verification of the irradiation history or the completeness of the fuel assembly and its integrity (i.e. the absence of pin removal or substitution). Neutron, gamma and Cerenkov light emissions are observables used to confirm burnup, cooling time and the completeness of spent fuel items. These are the three main parameters indirectly characterizing spent fuel assemblies from a safeguards standpoint. This paper describes the merits and limitations of methods and instruments currently approved and employed in spent fuel verification, with a focus on partial defect testing. The effectiveness and efficiency of the different options are compared, and an update given on alternatives currently being developed within the framework of the IAEA Member State Support Programme. Finally, the paper provides a vision of how IAEA requirements for LWR spent fuel verification might evolve in the future.