Spent fuel modeling and simulation using ORIGAMI for advanced NDA instrument testing

The Next Generation Safeguards Initiative Spent Fuel project funded by the National Nuclear Security Administration is at the final phase of developing several advanced nondestructive assay (NDA) instruments to provide improved capabilities for spent fuel safeguards, including detection of partial defects, verification of operator declarations, and quantification of plutonium content. Field tests of several instruments have been completed at facilities in Republic of Korea and Japan. Recent activities have focused on 25 PWR and 25 BWR spent fuel assemblies with diverse attributes at the Central Spent Fuel Interim Storage Facility in Sweden. Measurement campaigns have been initiated and will continue over the next two years, including gamma-ray spectroscopy, Fork detector, calorimetry, and several advanced NDA instruments such as Differential Die-away Self Interrogation, Differential Die-away, and Californium Interrogation Prompt Neutron methods. As part of the field testing, high-fidelity computer models of the spent fuel assemblies and the NDA instruments are needed to help assess the instrument performance. Such models are also essential for correlating the response of one instrument to that of another. These assembly models should provide well-characterized nuclide inventories and the passive neutron and gamma ray emission spectra. A new three-dimensional assembly depletion capability, ORIGAMI, has been developed recently at Oak Ridge National Laboratory to provide a convenient interface to the ORIGEN code in SCALE. This paper will describe how ORIGAMI was used to develop the assembly models using detailed fuel assembly design and reactor operating data, and demonstrate some results generated by this code. Comparison of these results with experimental data will be reported once the experimental data are published in the near future.