Screening of uranium surface contamination on demolition debris by TXRF analysis

With the progressing decommissioning of the Fukushima Daiichi Nuclear Power Plant, the possibility that demolition debris could be contaminated with uranium will increase. Total reflection X-ray fluorescence (TXRF) analysis has been used to detect trace uranium in water [1-3]. Thus, it is likely that TXRF analysis of acid elution solution of demolition debris samples could be used to evaluate uranium surface contamination on demolition debris. In this study, we developed a methodology for screening of uranium surface contamination on demolition debris using TXRF analysis. As a model of surface shavings of contaminated demolition debris, a series of uranium solutions with different concentrations were placed on 5 g of crashed concrete/soil mixtures and dried. Subsequently, 20 mL of 4 M nitric acid solution was added to the samples and shaken for 30 min. After filtration using a hydrophilic polyvinylidene difluoride membrane (pore size of 0.1 µm), chromatography resin separation was performed. During this step, uranium was separated from the native elements of the soil and concrete including iron (present in soil and concrete in large concentrations), calcium (present in concrete in large concentrations), and rubidium whose Kα line overlaps that of the U Lα line. Bromine, with a Kβ line that also overlaps the U Lα line, remained in solution more than the other elements tested and the U Lα peak was easily separated from the Br Kβ peak by Gaussian fitting. For the TXRF measurements, 190 μL of the sample solutions were mixed with 10 μL of a 100 μg/mL gallium standard. Subsequently, 10 μL of the resulting mixture was dropped onto a fluorine resin-coated glass slide and dried for ~5 min using a heater at 80 °C. TXRF measurements were performed using a benchtop-type TXRF instrument (NANOHUNTER-II, Rigaku Corporation, Tokyo, Japan). The uranium contents of the sample solutions were higher than the spiked uranium contents due to uranium elution from the soil and concrete. This method will be useful for screening of contaminated demolition debris. This research project was conducted as regulatory supporting research funded by the Secretariat of Nuclear Regulation Authority (S/NRA/R), Japan.[1] Matsuyama et al., J. Nucl. Sci. Technol. 54, (2017), 940.[2] Yoshii et al., Spectrochim. Acta Part B 148, (2018) 183.[3] Matsuyama et al., Spectrochim. Acta Part B 149, (2018), 35.18th International Conference on Total Reflection x-ray Fluorescence Analysis and Related Methods (TXRF2019