Synthesis and characterisation of PuPO₄ - a potential analytical standard for EPMA actinide quantification

Abstract

Abstract. Transmutation nuclear fuels contain weight percentage quantities of actinide elements, including Pu, Am and Np. Because of the complex spectra presented by actinide elements using electron probe microanalysis (EPMA), it is necessary to have relatively pure actinide element standards to facilitate overlap correction and accurate quantitation. Synthesis of actinide oxide standards is complicated by their multiple oxidation states, which can result in inhomogeneous standards or standards that are not stable at atmospheric conditions. Synthesis of PuPO 4 results in a specimen that exhibits stable oxidation-reduction chemistry and is sufficiently homogenous to serve as an EPMA standard. This approach shows promise as a method for producing viable actinide standards for microanalysis. IntroductionNuclear fuels are being developed for next-generation nuclear reactors (GEN-IV) that have the ability to burn Pu, Am, and Np from spent nuclear fuels. Upon irradiation, these so-called transmutation fuels convert long-lived minor actinide elements (MA) to shorter-lived fission products, thereby decreasing the radiotoxicity and heat load of spent nuclear fuel.The thermodynamic behaviour of MA is unlike that of uranium in conventional nuclear fuels. Moreover there is much greater variation in the chemical and isotopic composition of transmutation fuels, such that they cannot be considered to be a simple extension of extant fuels [1].Because of these features, considerable research and development is required for both fabrication and analysis of transmutation fuels. Integral to the fabrication and analysis of irradiated fuel is electron probe microanalysis (EPMA). This technique has been used since at least 1961 [2] for the analysis of nuclear fuels because wavelength dispersive spectrometers permit better separation of complex peaks, such as those exhibited by the actinide metals group, than is possible with energy dispersive detectors.Reference materials are necessary to calibrate the instrument in order to obtain an accurate MA measurement. While some progress has been made with regard to creating models for standardless analysis [3], such efforts are still in their infancy. Therefore, nuclear fuels researchers still rely on the use of physical standards for the analysis of MA. Unfortunately, fabrication and use of such standards is fraught with difficulty. All fabrication and polishing must be done in special nuclear-grade facilities. Such facilities typically include glove boxes with prescribed atmospheres, and remote handling tools. Metal specimens are relatively easy to handle, but when exposed to oxygen, will oxidise very rapidly.

Improved Protocol for the Quantification of Actinides (Th, U, Np, Pu, Am, and Cm) Using Electron Probe Microanalysis

“…Second, microprobe counting detectors and other sensitive parts in the column are exposed to high β- and γ-irradiation from the samples, which demands special and costly shielding (Walker, 1999; Lamontagne et al, 2007; Walker et al, 2012). Third, well-polished surfaces are crucial for the quality of quantitative analysis using EPMA, yet all of the common sample preparation steps such as embedding, grinding, polishing, and controlling the polishing status under a microscope have to be carried out in glove boxes (Walker, 1999; Lamontagne et al, 2007; Wright et al, 2018), but these “simple” steps are not necessarily available all in one glove box. Thus, every approach in sample transportation imposes a risk of destroying or even losing the sample.…”

“…Thus, every approach in sample transportation imposes a risk of destroying or even losing the sample. These obstacles during preparation for microanalysis occur next to complications in fabrication methods (Wright et al, 2018) or policy and logistical issues during transportation.…”