Advances in Spent Fuel Libraries

For the purpose of quantifying how a wide range of nondestructive assay techniques are expected to perform when measuring spent fuel assemblies, the Next Generation Safeguards Initiative (NGSI) Spent Fuel NDA Project has produced six sets of virtual Light Water Reactor (LWR) spent fuel assemblies. The first library was created using infinitely-reflected boundary conditions for different integer values of initial enrichment, burnup, and cooling time in a Pressurized Water Reactor (PWR). The second library consisted of more realistic irradiation conditions with a 1/8 core geometry model of a PWR and shuffling of fuel assemblies. The third library again used infinitelyreflected boundary conditions and examined variations to the operating conditions and the presence of materials such as burnable poisons within a PWR fuel assembly. Initial simulations of NDA instruments performed for the NGSI Spent Fuel Project used primarily Spent Fuel Libraries (SFL) 1 and 2, though these libraries comprised a limited set of operating conditions. Calculations are being expanded to SFL3 for uncertainty analyses to quantify how realistic changes in operating conditions affect NDA signals. Two new libraries (SFL4 and SFL5) were also developed this year for the NGSI Spent Fuel Project and for the Swedish Nuclear Fuel and Waste Management Company (SKB) respectively. SKB needed Boiling Water Reactor (BWR) assemblies produced to properly asses the NDA need of the Swedish Encapsulation Facility (CLINK). The purpose of generating SFL4 was to provide a library of “unknown” PWR assemblies to: 1) test the predictive capability of various NDA systems to predict the Pu mass, 2) provide uncertainty of analysis approaches developed to date, and 3) validate completeness and correctness of the declared assemblies. The integrated systems will be used to determine the plutonium mass solely from signals, and the final results will be compared to the simulated masses. Finally, a third new library (SFL6) will be developed for gamma emission tomography with more types of reactors and potential partial defect (i.e., diversion) scenarios. This work is supported by NGSI, Office of Nonproliferation and International Security, National Nuclear Security Administration and SKB.