Year
2017
Abstract
Safeguards verification of nuclear materials (NMs) depends upon the timely detection of misuse within a facility. To improve current capabilities, the Japan Atomic Energy Agency is collaborating with the EC Joint Research Centers (JRC) to develop a comprehensive system that combines four active, neutron-interrogation non-destructive assay techniques to measure small samples of mixed NM (e.g. spent fuel solution, Pu-Nitrate, and MOX). The delayed gamma-ray spectroscopy (DGS) technique being incorporated into the system can determine fissionable nuclide ratios by correlating the observed time-dependent gamma-ray energy spectrum to the unique fission product (FP) yield of the individual nuclides. While the mixed NM generates high passive gamma-ray emissions, these can be suppressed with shielding while the DGS technique can utilize the high-energy region of the short-lived FPs that produce gamma rays well in excess of 3-MeV. In order to quantify the fissile NM (e.g. 235U, 239Pu, and 241Pu), the neutrons interrogating the sample must be near thermal energies where the fissile nuclides have large cross-sections. However, the compact, transportable neutron sources available produce energies between 1- and 14-MeV (e.g. 252Cf and D-T generators). In order to effectively use DGS, moderators must be developed to reduce the energy of the interrogation neutrons while maintaining large fluxes to provide significant FP signals. Experiments are underway to improve the observation and quantification of the high-energy FP gamma rays using the Pulsed Neutron Interrogation Test Assembly (PUNITA) system at the JRC-Ispra site and other facilities. Using this data, neutron fluxes and measurement conditions are being used to develop a Monte Carlo (MC) that will then be used for analysis of the DGS data by an inverse MC (IMC) method. The DGS program described here summarizes the 3-year development to optimize the moderator, perform experiments, and create the IMC in preparation for a demonstration of the technique.