Trace Elements in Uranium Oxide
Combining Analytical Techniques for Trace Elements in Uranium Oxide (U3O8 )Traditionally XRF is used to analyse the major elements in a solid high purity product and ICP to analyse the trace elements in the dissolved solid; hence different sample preparation techniques are required. Laser Ablation Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS) as a technique can be used in parallel with X-ray Fluorescence (XRF) with the same analytical methodology. Trace elements present in U3O8 are investigated using LA-ICP-MS as these are below detection limits of XRF instruments.
Trace impurity concentrations in uranium materials are an important quality control parameter in the production of high-purity uranium metals of uranium oxides. Certain impurities can alter the physical characteristics of the high purity material and the neutron absorption characteristics of light impurity elements can attenuate nuclear processes in the material. This becomes very important when fuel for nuclear reactor is produced. A fast and accurate analytical method is essential for trace impurities, as exposure to the analyst must be kept to the minimum Crain et al (1992). LA-ICP-MS, is a vaporisation process in which a laser is used as the primary energy source. When a laser beam of sufficient power density strikes a solid material, it generates particle aerosols into the gas phase. This ablation process is caused by the interaction of laser photons with the solid material. ICP-MS is capable of providing a high throughput of samples while analysing at levels as low as parts per trillion (ppt). The elements in the sample are ionised in the high temperature argon plasma and then separated on the basis of their mass to charge ratio (m/z). Various sample introduction systems can be linked to the ICP-MS, including laser ablation, depending on what the sample matrix and concentration requires.
XRF is used to determine the elements present in a sample by studying the secondary fluorescent X-ray spectrum produced by the irradiated sample. It provides a high throughput of samples and is a non-destructive method. The samples are unchanged by the testing. The use of Lithium metaborate and Lithium tetraborate flux fusion was a major breakthrough for XRF sample preparation. Most geological samples are effectively dissolved by these fluxes to form homogenous glass. This is where LA-ICP-MS and XRF can be used in parallel as the same analytical methodology can be used.
The table below shows some of the trace elements present in the test sample.
ND denotes that element was below detection limit for the set counting condition.
Although trace elements in U3O8 can be measured accurately using LA-ICP-MS, XRF was found to be the best for the major component, which in this case was uranium. The lithium-borate fusion glass used for XRF can be made rapidly with a high degree of homogeneity. The advantage of combining LA-ICP-MS and XRF is that there is no additional sample preparation. Radioactive materials are easier to handle as the hazards are lower when they are dissolved in glass. It is easier to handle waste as it is already in a solid form. Further investigations are needed to perfect this technique for trace element analysis. The work carried out at ANSTO so far on LA-ICP-MS is at a developmental stage. We are in the process of gathering knowledge and expertise in this area and see more opportunities arising in the future for high quality analytical work.
REFERENCE
Crain J. S. and Gallimore D. L., (1992). "Determination of Trace Impurities in Uranium Oxides by Laser Ablation Inductively Coupled Plasma Mass Spectrometry", Journal of Analytical Atomic Spectrometry, Vol 7, 605-610.
Patricia Gadd, K.M. Marshall and Ned. Blagojevic
Australian Nuclear Science and Technology Organisation, Lucas Heights , NSW 2234, Australia
Trace impurity concentrations in uranium materials are an important quality control parameter in the production of high-purity uranium metals of uranium oxides. Certain impurities can alter the physical characteristics of the high purity material and the neutron absorption characteristics of light impurity elements can attenuate nuclear processes in the material. This becomes very important when fuel for nuclear reactor is produced. A fast and accurate analytical method is essential for trace impurities, as exposure to the analyst must be kept to the minimum Crain et al (1992). LA-ICP-MS, is a vaporisation process in which a laser is used as the primary energy source. When a laser beam of sufficient power density strikes a solid material, it generates particle aerosols into the gas phase. This ablation process is caused by the interaction of laser photons with the solid material. ICP-MS is capable of providing a high throughput of samples while analysing at levels as low as parts per trillion (ppt). The elements in the sample are ionised in the high temperature argon plasma and then separated on the basis of their mass to charge ratio (m/z). Various sample introduction systems can be linked to the ICP-MS, including laser ablation, depending on what the sample matrix and concentration requires.
XRF is used to determine the elements present in a sample by studying the secondary fluorescent X-ray spectrum produced by the irradiated sample. It provides a high throughput of samples and is a non-destructive method. The samples are unchanged by the testing. The use of Lithium metaborate and Lithium tetraborate flux fusion was a major breakthrough for XRF sample preparation. Most geological samples are effectively dissolved by these fluxes to form homogenous glass. This is where LA-ICP-MS and XRF can be used in parallel as the same analytical methodology can be used.
The table below shows some of the trace elements present in the test sample.
ND denotes that element was below detection limit for the set counting condition.
Although trace elements in U3O8 can be measured accurately using LA-ICP-MS, XRF was found to be the best for the major component, which in this case was uranium. The lithium-borate fusion glass used for XRF can be made rapidly with a high degree of homogeneity. The advantage of combining LA-ICP-MS and XRF is that there is no additional sample preparation. Radioactive materials are easier to handle as the hazards are lower when they are dissolved in glass. It is easier to handle waste as it is already in a solid form. Further investigations are needed to perfect this technique for trace element analysis. The work carried out at ANSTO so far on LA-ICP-MS is at a developmental stage. We are in the process of gathering knowledge and expertise in this area and see more opportunities arising in the future for high quality analytical work.
REFERENCE
Crain J. S. and Gallimore D. L., (1992). "Determination of Trace Impurities in Uranium Oxides by Laser Ablation Inductively Coupled Plasma Mass Spectrometry", Journal of Analytical Atomic Spectrometry, Vol 7, 605-610.
Patricia Gadd, K.M. Marshall and Ned. Blagojevic
Australian Nuclear Science and Technology Organisation, Lucas Heights , NSW 2234, Australia