A novel methodology to detect diversion of spent fuel from pressurized water reactors (PWRs) has been developed in order to address a long unsolved safeguards verification problem for an international safeguards organization such as the International Atomic Energy Agency (IAEA) or European Atomic Energy Community (EURATOM). The concept involves inserting tiny neutron and gamma detectors into the guide tubes of a spent fuel assembly (SFA) and measuring the signals. The guide tubes form a quadrant symmetric pattern in the various PWR fuel product lines, and the neutron and gamma signals from these various locations are processed to obtain a unique signature for an undisturbed SFA. Signatures based on the neutron and gamma signals individually or in a combination can be developed. Removal of fuel pins from the SFA will cause the signatures to be visibly perturbed thus enabling the detection of diversion. All of the required signal processing to obtain signatures can be performed on standard laptop computers.

Monte Carlo simulation studies and a set of controlled experiments with actual commercial PWR SFAs were performed, and they validated this novel methodology. Based on the simulation studies and benchmarking measurements, the methodology promises to be a powerful and practical way to detect partial defects that constitute 10% or more of the total active fuel pins. This far exceeds the IAEA goal that for SFAs that can be dismantled at the facility - which is essentially the case for most PWR fuel - the partial defect test used should assure that at least half the fuel pins are present in each SFA. The methodology does not rely on any operator-provided data like burnup or cooling time and does not require movement of the SFA from the storage rack in the spent-fuel pool.