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|Title:||Application of the PDET detector to BWR fuel assemblies: gross defect testing using the spatial distribution of neutron and photon flux|
|Authors:||ROSSA Riccardo; PEERANI Paolo; HAM Young; SITARAMAN Shivakumar|
|Citation:||Proceedings of the 35th ESARDA Conference|
|Type:||Articles in periodicals and books|
|Abstract:||Over 80 per cent of the material placed under safeguards today is in the form of spent fuel and one of the main ways to verify it is by Non-Destructive Assays. The main goal for the safeguards inspections is to verify that some or all the material has not been diverted to other purposes by detecting the eventual gross or partial defect. The European Commission with the JRC-ITU located in Ispra in collaboration with Lawrence Livermore National Laboratory is studying the application of a detector to BWR fuel assemblies immersed in a spent fuel pool. The Partial Defect Tester (PDET) employs a set of neutron and photon detectors to be inserted in the fuel assembly to quantify the spatial distribution of the two fluxes within a PWR fuel assembly. The insertion of multiple detectors inside a PWR assembly does not have a major technical problem and has been investigated by the Lawrence Livermore National Laboratory. The situation changes when the same concept is applied to a BWR assembly. A generic BWR assembly contains less fuel pins compared to a PWR assembly, but inside a traditional BWR assembly there are fewer water holes since the control rods have a cruciform shape and are inserted between neighbouring fuel assemblies. The purpose of this study was to assess the feasibility of gross defect verification by evaluating the spatial distribution of both neutron and photon flux inside the BWR spent fuel assemblies. This study also gave an indication whether the irradiation history of the fuel assembly (burnup and cooling time) plays a role in the detection of the gross diversion. The results showed that the gross defect is detectable by looking at the normalized ratio between the neutron and gamma signal (N/P ratio) as well as the normalized neutron and gamma signals. In particular, the change in shape of the normalized gamma signal appears to be a good indicator of a gross defect independent of operator declarations, regardless of whether the storage rack has assemblies with varying or non-varying burnups and cooling times.|
|JRC Directorate:||Nuclear Safety and Security|
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