NDA techniques for spent fuel verification and radiation monitoring. Report on activities 6a and 6b of Task JNT C799 (SAGOR). Finnish support programme to the IAEA safeguards

A variety of NDA methods exist for measurement of spent fuel at various stages of the disposition process. Each of the methods has weaknesses and strengths that make them applicable to one or more stages in disposition. Both passive and active methods are, under favorable conditions, capable of providing either a mapping of an assembly to identify missing fuel pins or a measurement of the fissile content and some are capable of providing a mapping of a canister to identify missing assemblies or a measurement of the fissile content. However, a spent fuel measurement system capable of making routine partial defect tests of spent fuel assemblies is missing. The active NDA methods, in particular, the active neutron methods, hold the most promise for providing quantitative measurements on fuel assemblies and canisters. Application of NDA methods to shielded casks may not be practical or even possible due to the extent of radiation attenuation by the shielding materials, and none of these methods are considered to have potential for quantitative measurements once the spent fuel cask has been placed in a repository. The most practical approach to spent fuel verification is to confirm the characteristics of the spent fuel prior to loading in a canister or cask at the conditioning facility. Fissile material tracking systems in addition to containment and surveillance methods have the capability to assure continuity of the verified knowledge of the sample from loading of the canisters to final disposal and closing of the repository. (orig.)