Developing Delayed Gamma-ray Spectroscopy for Reprocessing Plant Nuclear Safeguards: Fissile Nuclide Content Analysis

The Japan Atomic Energy Agency’s Integrated Support Center for Nuclear Nonproliferation and Nuclear Security (JAEA/ISCN) and European Commission Joint Research Centre (EC/JRC) are collaborating to develop technology for nuclear safeguards verification. Delayed gamma-ray spectroscopy (DGS) is being developed to supplement the verification of nuclear material in reprocessing plants by analyzing the fissile nuclide content in spent nuclear fuel solution samples. DGS is an active-interrogation non-destructive assay technique that uses an external neutron source to induce fission in the sample followed by a measurement of gamma rays emitted by the decay of the generated fission products. Experiments were performed with the PUNITA instrument at the EC/JRC in Ispra, Italy to obtain spectra from both U and Pu samples. These were used to evaluate the gamma-ray peak dependence on both the interrogation pattern as well as the enrichment. Analysis of these spectra has resulted in clear distinction between the
²³⁵
U and
²³⁹
Pu fissile nuclide spectra for composition analysis as well as a linear correlation to the
²³⁵
U mass. Experiments with the JAEA/ISCN’s Delayed Gamma-ray Test Spectrometer in the EC/JRC PERLA facility show spectral results similar to PUNITA, even as a more compact instrument. These results are compared to the JAEA/ISCN Delayed Gamma-ray Spectroscopy Monte Carlo (DGSMC) and other simulation codes for validation and final evaluation of an inverse Monte Carlo analysis method. This work will describe the goals of the DGS project along with the experimental results in light of the efforts to develop the DGSMC for analysis of current and future applications.