Ruggedized, High-Resolution CZT Spectrometer for Operation in Inert Hot Cells

Effective nuclear material accounting and control in international safeguards requires tools capable of monitoring the use of special nuclear materials. Argon-filled hot cells, which are commonly used in fuel fabrication, represent a safeguards “blind spot” where traditional radiation detectors used in non-destructive assay struggle to operate. Furthermore, the poor spectral quality of even modern scintillator-based detectors complicates quantitative safeguards under normal atmospheric conditions. This effort aims to address both problems, the difficulty in operating detectors in an argon environment and poor scintillator-based quantitative safeguards, by leveraging high-performance, ruggedized, 3-D pixelated CdZnTe detectors with better than 1.0% energy resolution.Phase I thoroughly tested commercial 3-D pixelated CdZnTe in argon atmospheres both locally and at a government collaborator facility. Stable, month-long CdZnTe operation in argon environments was achieved by under-biasing systems to mitigate sparking. Furthermore, Phase I demonstrated the compatibility of pixelated CdZnTe spectrometers with current commercial safeguards software and existing web monitoring databases developed for commercial nuclear power. Compton radiation imaging, which is intrinsic to 3-D pixelated CdZnTe detectors, was demonstrated for hot cell surveys using 137Cs at reduced operational biases. Finally, system stability, which is critical for accurate, quantitative safeguards measurements, was validated across a large ambient temperature range of 15-50°C and incident count rates of 0-30 thousand counts per second. In conclusion, all technical objectives proposed in Phase I were met or exceeded, providing momentum towards Phase II.In Phase II, we will build an additional CdZnTe detector prototype for hot cell measurements to use along with the detector utilized in Phase I. One system will be kept on-site to demonstrate continuous operation over six months under argon atmosphere. Another system will be used in phased validation testing at a collaborating government laboratory with the eventual goal of deployment in spent fuel hot cells. Measurements at the fuels processing complex will be conducted to support existing nuclear material accounting measurements. Finally, continued improvements to existing webserver software will be made to improve CdZnTe detector capabilities as a process monitor. Once completed, this commercial CdZnTe detector will represent the state-of-the-art hot cell spectroscopy safeguards systems.Reliable, rigorously tested CdZnTe spectrometers will improve the accuracy of hot cell assays. This will improve the efficacy of international safeguard regimes, helping to prevent the spread of nuclear weapons. Furthermore, automating safeguards analysis through close coupling with commercial safeguards software and existing monitoring codes will benefit society by freeing up workers to focus on other safeguards critical tasks. These advances in system reliability, such as spark mitigation, will have implications in other markets like space measurements. In practice, the work conducted under this Phase II program will represent a quantum leap in quantitative hot cell-based safeguards.