PARTIAL DEFECT VERIFICATION USING THE DCVD: A CAPABILITY EVALUATION APPROACH

The Digital Cherenkov Viewing Device (DCVD) is a non-intrusive instrument available to the International Atomic Energy Agency (IAEA) for verifying spent nuclear fuel in storage pools. It is currently used for gross-defect evaluations, i.e. to verify that an item in a storage pool is an irradiated fuel assembly and not a fresh assembly or a dummy. This is done by recording images of the Cherenkov light emitted in the water surrounding the fuel. Currently, the instrument’s ability to also detect partial defects at the 50% level or even lower is under study. Here, experimental work is complimented by modeling and simulations due to the limited availability of assemblies with partial defects. Ideally, an IAEA inspector should be able to use the DCVD at e.g. a fuel storage site and immediately after scanning obtain information on (1) whether an item is an irradiated fuel assembly or not, and (2) whether the assembly is intact or suffers from a partial defect. This paper discusses a decision-making methodology intended for the latter purpose with the objective to implement it in the DCVD software in order to facilitate smooth inspection procedures. Inspectors will thus not be required to possess any expertise in the decision-making methodology. The paper also describes measurements performed during spring 2011 at the CLAB interim spent fuel storage in Sweden. The measurements were carried out with the objective to optimize the equipment handling and work flow during this type of measurement campaigns and to form a basis for the evaluation of the DCVD’s ability to detect partial defects.