Study of Chemical Changes in Uranium Oxyfluoride Particles Progress Report June 2008 - February 2009

Kips, R S ; Kristo, M J ; Hutcheon, I D

关键词: ACCURACY;    CHEMICAL COMPOSITION;    CRYOGENICS;    FLUORESCENCE;    FLUORINE;    HUMIDITY;    HYDROLYSIS;    MASS SPECTROMETERS;    MORPHOLOGY;    OXYFLUORIDES;    PROGRESS REPORT;    RAMAN SPECTROSCOPY;    SAMPLING;    SENSITIVITY;    SPATIAL RESOLUTION;    SPECTROSCOPY;    TRANSFORMATIONS;    URANIUM;    URANIUM COMPOUNDS;    URANIUM ISOTOPES;   

DOI  :  10.2172/948970
RP-ID  :  LLNL-TR-410890
PID  :  OSTI ID: 948970
Others  :  TRN: US0901881

美国|英语

来源: SciTech Connect

【 摘 要 】

The present study aims to demonstrate how knowledge of time-dependent changes in uranium oxyfluoride particles can benefit particle analyses for environmental sampling. Environmental sampling depends upon laboratory analysis of nuclear material that has often been exposed to the environment after it was produced. It is therefore important to understand how those environmental conditions might have changed the chemical composition of the material over time. To investigate this, we prepared a set of uranium oxyfluoride particles at the Institute for Reference Materials and Measurements (IRMM-DG Joint Research Centre of the European Commission, Belgium). These UO{sub 2}F{sub 2} particles were prepared from the release and subsequent hydrolysis of UF{sub 6} gas, and were stored at LLNL in environmental chambers, set to different humidity, temperature and lighting conditions. An experimental plan was drafted to assess the number of analyses required to track the changes in particle composition, morphology, and structure. Due to its high spatial resolution and excellent transmission, the NanoSIMS secondary ion mass spectrometer at LLNL was found to be the optimal tool to measure individual oxyfluoride particles. This was confirmed by our participation in the inter-laboratory measurement campaign for particle analysis (NUSIMEP-6), organized by the IRMM in June last year. The reported uranium isotope ratios demonstrated the precision and accuracy of the NanoSIMS and ims 3f SIMS measurements at LLNL, and provided a high degree of confidence that the new measurements on the UO{sub 2}F{sub 2} samples will be of comparable high quality. As fluorine is known to be a chemically-sensitive compound, we measured the intensity of the fluorine secondary ions relative to the ions generated by the matrix to evaluate the rate of particle degradation under different environmental conditions. A relative sensitivity factor was empirically determined to convert these measurements to absolute fluorine concentrations. Additional measurements in selected uranium compounds were carried out to account for variations in matrix composition. Because of the complexity of both the SIMS instruments, as well as the nature of the samples, we spent a substantial amount of time on instrument training and instrument set up. The latest NanoSIMS measurements on the freshly-prepared UO{sub 2}F{sub 2} particles however, showed that we are on the right track when it comes to determining the chemical changes in individual uranium particles. At PNNL, several optical techniques including cryogenic laser-induced time-resolved U(VI) fluorescence micro-spectroscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy will be applied to investigate molecular transformations of the particles. As a control, dynamic SIMS measurements will also be performed on a subset of the samples sent to PNNL.