Presentation TXRF analysis of uranium in acid elution solution model of soil

Yoshii, Hiroshi  ,  Izumoto, Yukie  ,  Matsuyama, Tsugufumi  ,  Ishii, Kota  ,  Sakai, Yasuhiro

2018-06-28
Description
In the decommissioning field of the Fukushima Daiichi Nuclear Power Plant, several kinds of waste contaminated with radionuclides were discharged. Although uranium has not been detected in the waste till now, there is a possibility of finding uranium on the surface of the waste in the near future. Because radioisotopes of uranium rarely emit easily detectable α- and γ-rays, quantification of uranium in the waste by radiation measurement is difficult. It is thought that the most suitable method for this purpose is mass analysis of an acid elution solution of waste by inductively coupled plasma mass spectrometry (ICP-MS). Total reflection X-ray fluorescence analysis (TXRF) is another potential technique to estimate uranium in an acid elution solution of waste. Although ICP-MS has higher detection sensitivity than TXRF, the time-consuming ashing process, which is required for decomposition of organic matter in the pretreatment for ICP-MS analysis, is not required for TXRF analysis. In the present study, TXRF analysis of uranium in a model of acid elution solution of waste was performed, and the potential of TXRF as a screening method for contamination level of uranium in the acid elution solution of waste was discussed.Uncontaminated dried soil, with diameter less than 2 mm, was employed as a model of dried sludge. Accurately metered dried soil was added to uranium-containing nitric acid, the uranium concentration of which was set to 1 ppm. After 30 min of shaking, the solution was filtered. Thus, a model of acid elution solution of uranium-contaminated waste could be produced. Uranium in the model solution was extracted by chromatography resin separation. A small amount of the sample solution was placed on a glass sample holder after mixing with indium standard solution employed as an internal standard and was subjected to TXRF measurement using a benchtop type TXRF spectrometer, NANOHUNTER-II (Rigaku, Japan).In the measured TXRF spectrum, the peaks of U Lα and Th Lα were found, because thorium can also be extracted by chromatography resin separation. The net peak intensities were obtained by Gaussian fitting. The measured uranium concentration in the sample solution was 1 ppm, same as that of the uranium-containing nitric acid, which implies that the collection rate of uranium was approximately 100%. The detection limit of uranium was calculated as 5 ppb. Hence, this method can be useful for screening of uranium contamination level on the surface of nuclear waste. This research project has been conducted as a regulatory supporting research funded by the Secretariat of Nuclear Regulation Authority (S/NRA/R), Japan.
European Conference on X-ray Spectrometry(EXRS2018)

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