Application of the PDET detector to BWR fuel assemblies: gross defect testing using the spatial distribution of neutron and photon flux

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.E.8-Nuclear securit

ESARDA Bulletin n. 59

ESARDA is an association initially formed to advance and harmonize research and development for nuclear safeguards whose scope has in recent year expanded as the number and type of its working groups’ activities below indicates. Esarda is currently composed of about 30 laboratories, private and governmental institutions worldwide. Within Esarda (http://esarda.jrc.ec.europa.eu/), a number working groups have been over the years established and active namely: Techniques and Standards for Destructive Analysis, Techniques and Standards for Non-Destructive Analysis, Containment and Surveillance, Novel Approaches / Novel Technologies, Implementation of Safeguards, Verification Technologies and Methodologies, Training and Knowledge Management, Editorial Committee. ESARDA publishes a Bulletin containing peer reviewed scientific related to nuclear Safeguards, verification and non-proliferation. This publication appears generally twice a year. In addition, thematic special issues are published as proposed by the ESARDA community. The Bulletin Editorial Board is composed of about 10 experts in the various technical and scientific fields related to safeguards. They are all actively engaged in safeguards R&D or in safeguards implementation and other fields. The Editorial Board decides the contents of the Bulletin, selects the papers to be published and reviews them before publication. All ESARDA editorial activities are carried out at JRC in Ispra. Scientific papers submitted for publication are reviewed by independent authors and by members of the Editorial Committee. The Bulletin is currently submitted to Scopus for evaluation in view of citation. ESARDA Bulletin is published jointly by ESARDA and the Joint Research Centre of the European Commission and distributed free of charge to over 1000 registered members, libraries and institutions worldwide.JRC.G.II.7-Nuclear securit