A nondestructive assay (NDA) instrument, conceptualized, designed, and fielded by Los Alamos National Laboratory (LANL), was deployed at the Clab interim spent fuel storage facility in Oskarshamn, Sweden. It is the first time differential die-away (DDA) techniques have been used to measure commercial spent nuclear fuel assemblies. The measurements were performed on a set of 25 pressurized water reactor (PWR) and boiling water reactor (BWR) fuel assemblies. The fuel was interrogated with a deuterium tritium (DT) neutron generator and the response measured with 12 He-3 tubes and a fission chamber. The resulting list-mode data was recorded for stationary locations as well as for axial scans of the assemblies. The DDA instrument was developed as part of a larger spent fuel project to provide a suite of novel tools and technologies to further current safeguards practices. The objectives of the spent fuel project have been to enhance the following capabilities: verification of facility declaration of initial enrichment, burnup, and cooling time; detection of diversion or replacement of fuel pins; estimation of fissile masses and decay heat; and measurement of multiplication of spent fuel assemblies. The DDA instrument was designed to incorporate all of these capabilities with the exception of decay heat. This paper presents the initial results and analysis of the Clab DDA measurements. These results suggest that the DDA technique can provide a significant capability advancement for a multitude of safeguards objectives. Specifically, a DDA type instrument could provide future permanent spent fuel repositories a means to efficiently and accurately assay and re-verify spent fuel prior to permanent disposition.
Year
2020
Abstract