Signatures for Different PWR Assemblies using Partial Defect Tester (PDET)

The Partial Defect Tester (PDET) produces a unique set of three signatures in Pressurized Water Reactor (PWR) spent fuel assemblies (SFAs) based on normalized neutron, gamma, and gamma-to-neutron signals that are principally dependent on the geometric layout of the guide tubes present in the assembly where the signal measurements are taken. Removal of as few as 10% of pins from an assembly have been shown to be detectable in several simulation studies which have been benchmarked with measurements performed in SFAs. The bulk of the studies conducted so far were performed with the 14x14 type of assemblies. This study expands the applicability of the PDET methodology to other type of SFAs such as 16x16 or 17x17 assemblies which also show symmetric signatures that are principally dependent on the quadrant symmetric layout of the guide tubes. The signatures from these larger assemblies also show that diversion of as few as 10% pins can be detected using PDET. In addition, in the interests of economy, this study examined the possibility of using fewer than all the available guide tube locations in a SFA, thus reducing the number of detectors needed, and still be able to detect diversion. At this time the conclusion was that more studies would be needed to ensure the feasibility of this approach and that, for now, it would be useful to have measurements at all locations and have all the data possible to ensure detection of diversion.