Gamma spectrometry of uranium and plutonium

The JRC-Karlsruhe tested the FRAM software's ability to accurately determine the isotopic composition of shielded uranium and plutonium. Over 17 000 spectra of certified reference materials were analysed using different FRAM parameter sets. The performance of FRAM was evaluated based on shielding thickness, measurement time, isotopic composition, and spectrum quality. 

For uranium analysis, a new FRAM parameter set was developed, providing more accurate results than the default sets. For plutonium the default parameter sets were found to be optimal. As nuclear material is frequently stored in shielded containers, these results are relevant for the daily work of nuclear safeguards inspectors in the field. More on the ESARDA Bulletin n. 60

The X-ray fluorescence (XRF) peaks of bismuth impact the determination of ²³⁵U enrichment by gamma spectrometry. Figure shows the overlapping peaks. These XRF peaks are present in most spectra recorded by germanium detectors built after 2003, due to bismuth in the new detectors, and in spectra of reprocessed uranium and of some cladded uranium fuel, due to bismuth in these materials. 

The JRC-Karlsruhe found that bismuth in the detector causes a bias of about 3% in the measured ²³⁵U enrichment. If bismuth cannot be avoided, bias correction or increased reported uncertainty should be considered. Detector manufacturers were informed and already provided bismuth-free detectors for safeguards. More in JNMM Volume 50, Issue 1

MRGS is increasingly used for in-field nuclear safeguards measurements due to its portability and ease of maintenance. However, there is still room for improvement in related spectra analysis software. 

The JRC-Karlsruhe collected high-quality medium-resolution spectra of certified uranium and plutonium reference materials using CdZnTe and LaBr3 detectors, in collaboration with the IAEA. These spectra are crucial for developing and validating spectrum analysis algorithms.