Study on the relation between the crystal structure and thermal stability of FeUO and CrUO

Akiyama, Daisuke*; Kusaka, Ryoji; Kumagai, Yuta; Nakada, Masami; Watanabe, Masayuki; Okamoto, Yoshihiro; Nagai, Takayuki; Sato, Nobuaki*; Kirishima, Akira*

Journal of Nuclear Materials, 568, p.153847_1 - 153847_10, 2022/09

https://doi.org/10.1016/j.jnucmat.2022.153847

FeUO, CrUO, and FeCrUO are monouranates containing pentavalent U. Even though these compounds have similar crystal structures, their formation conditions and thermal stability are significantly different. To determine the factors causing the difference in thermal stability between FeUO and CrUO, their crystal structures were evaluated in detail. A Raman band was observed at 700 cm in all the samples. This Raman band was derived from the stretching vibration of the O-U-O axis band, indicating that FeCrUO was composed of a uranyl-like structure in its lattice regardless of its "x"' value. Mssbauer measurements indicated that the Fe in FeUO and FeCrUO were trivalent. Furthermore, FeCrUO lost its symmetry around Fe with increasing electron densities around Fe, as the abundance of Cr increased. These results suggested no significant structural differences between FeUO and CrUO. Thermogravimetric measurements for UO, FeUO, and CrUO showed that the temperature at which FeUO decomposed under an oxidizing condition (approximately 800 C) was significantly lower than the temperature at which the decomposition of CrUO started (approximately 1250 C). Based on these results, we concluded that the decomposition of FeUO was triggered by an ``in-crystal'' redox reaction, i.e., Fe U Fe U, which would not occur in the CrUO lattice because Cr could never be reduced under the investigated condition. Finally, the existence of Cr in FexCrUO effectively suppressed the decomposition of the FeCrUO crystal, even at a very low Cr content.

Identification of altered phases of fuel debris by laser fluorescence spectroscopy (Contract research); FY2020 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; The University of Tokyo*

JAEA-Review 2022-007, 59 Pages, 2022/06

JAEA-Review-2022-007.pdf:2.09MB

The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2020. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2018, this report summarizes the research results of the "Identification of altered phases of fuel debris by laser fluorescence spectroscopy" conducted from FY2018 to FY2021 (this contract was extended to FY2021). Since the final year of this proposal was FY2021, the results for four fiscal years were summarized. The present study aims to identify alteration phases occurring on the surface fuel debris at various conditions, using time-resolved laser fluorescence spectroscopy (TRLFS), which is a selective analytical technique for U(VI), a major constituent of fuel debris and stable in oxidizing conditions. In particular, we pursue to improve its sensitivity and resolution by performing measurements at ultra-low temperature and identify multiple and heterogeneous U(VI)

Developing accelerator mass spectrometry capabilities for anthropogenic radionuclide analysis to extend the set of oceanographic tracers

Hain, K.*; Martschini, M.*; Glce, F.*; Honda, Maki; Lachner, J.*; Kern, M.*; Pitters, J.*; Quinto, F.*; Sakaguchi, Aya*; Steier, P.*; et al.

Frontiers in Marine Science (Internet), 9, p.837515_1 - 837515_17, 2022/03

https://doi.org/10.3389/fmars.2022.837515

Recent major advances in accelerator mass spectrometry (AMS) at the Vienna Environmental Research Accelerator (VERA) regarding detection efficiency and isobar suppression have opened possibilities for the analysis of additional long-lived radionuclides at ultra-low environmental concentrations. These radionuclides, including U, Cs, Tc and Sr, will become important for oceanographic tracer application due to their generally conservative behavior in ocean water. In particular, the isotope ratios U/U and Cs/Cs have proven to be powerful fingerprints for emission source identification as they are not affected by elemental fractionation. Improved detection efficiencies allowed us to analyze all major long-lived actinides, i.e. U, Np, Pu, Am as well as the very rare U, in the same 10 L water samples of an exemplary depth profile from the northwest Pacific Ocean. Especially for Sr analysis, our new approach has already been validated for selected reference materials (e.g. IAEA-A-12) and is ready for application in oceanographic studies. We estimate that a sample volume of only (1-3) L ocean water is sufficient for Sr as well as Cs analysis, respectively.

Identification and quantification of a Co radiation source under an intense Cs radiation field using an application-specific CeBr spectrometer suited for use in intense radiation fields

Kaburagi, Masaaki; Shimazoe, Kenji*; Kato, Masahiro*; Kurosawa, Tadahiro*; Takahashi, Hiroyuki*

Journal of Nuclear Science and Technology, 10 Pages, 2022/02

https://doi.org/10.1080/00223131.2022.2026833

spectrometry of terrestrial gamma rays using portable germanium detectors in area of 80 km radius around the Fukushima Daiichi Nuclear Power Plant

Mikami, Satoshi; Tanaka, Hiroyuki*; Okuda, Naotoshi*; Sakamoto, Ryuichi*; Ochi, Kotaro; Uno, Kiichiro*; Matsuda, Norihiro; Saito, Kimiaki

Nihon Genshiryoku Gakkai Wabun Rombunshi, 20(4), p.159 - 178, 2021/12

https://doi.org/10.3327/taesj.J20.010

In order to know the background radiation level where the area affected by the Fukushima Daiichi Nuclear Power Plant accident in 2011, terrestrial gamma rays had been measured by using portable germanium detectors repeatedly from 2013 through 2019, at 370 locations within 80 km radius area centered on the Fukushima Daiichi Nuclear Power Plant. Radioactive concentrations of Uranium 238, Thorium 232, Potassium 40 and kerma rates in air due to terrestrial gamma rays were obtained at those locations based on the method of ICRU report 53. Averaged concentrations of U, Th and K were 18.8, 22.7, 428 Bq/kg, respectively, and kerma rate in air over the area was found to be 0.0402 Gy/h. The obtained kerma rates in air were compared to those reported in literatures. It was confirmed that the data were correlated with each other, and were agreed within the range of their uncertainty. This is because the kerma rate in air due to terrestrial gamma rays is depend on geology. The similar trend to previous findings was observed that the kerma rate in air at locations geologically classified as Mesozoic era, Granite and Rhyolite were statistically significantly higher than the others.

Development of the multi-cubic -ray spectrometer and its performance under intense Cs and Co radiation fields

Kaburagi, Masaaki; Shimazoe, Kenji*; Kato, Masahiro*; Kurosawa, Tadahiro*; Kamada, Kei*; Kim, K. J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*

Nuclear Instruments and Methods in Physics Research A, 1010, p.165544_1 - 165544_9, 2021/09

https://doi.org/10.1016/j.nima.2021.165544

The number of nuclear facilities being decommissioned has been increasing worldwide, in particular following the accident of the Tokyo Electric Power Company Holdings' Fukushima Daiichi Nuclear Power Station in 2011. In these nuclear facilities, proper management of radioactive materials is required. Then, A -ray spectrometer with four segmentations using small volume CeBr scintillators with a dimension of was developed. The four scintillators were coupled to a multi-anode photomultiplier tube specific to intense radiation fields. We performed the -ray exposure study under Cs and Co radiation fields. Under the Cs radiation field, the relative energy resolution at 1375 mSv/h was the relative energy resolution at 1375 mSv/h was 9.20.05%, 8.00.08%, 8.00.03%, and 9.00.04% for the four channels, respectively.

First determination of the spin and parity of the charmed-strange baryon

Moon, T. J.*; Tanida, Kiyoshi; Belle Collaboration*; 203 of others*

Physical Review D, 103(11), p.L111101_1 - L111101_9, 2021/06

https://doi.org/10.1103/PhysRevD.103.L111101

Incorporation of U, Pb and rare earth elements in calcite through crystallisation from amorphous calcium carbonate; Simple preparation of reference materials for microanalysis

Miyajima, Yusuke*; Saito, Ayaka*; Kagi, Hiroyuki*; Yokoyama, Tatsunori; Takahashi, Yoshio*; Hirata, Takafumi*

Geostandards and Geoanalytical Research, 45(1), p.189 - 205, 2021/03

https://doi.org/10.1111/ggr.12367

Uncertainty for elemental and isotopic analyses of calcite by LA-ICP-MS is largely controlled by the homogeneity of the reference materials (RMs) used for normalization and validation. In order to produce calcite RMs with homogeneous elemental and isotopic compositions, we incorporated elements including U, Pb, and rare earth elements into calcite through heat- and pressure-induced crystallization from amorphous calcium carbonate that was precipitated from element-doped reagent solution. X-ray absorption spectra showed that U was present as U(VI) in the synthesized calcite, probably with a different local structure from that of aqueous uranyl ions. The uptake rate of U by our calcite was higher in comparison to synthetic calcite of previous studies. Variations of element mass fractions in the calcite were better than 12% 2RSD, mostly within 7%. The Pb/Pb ratio in the calcite showed 1% variations, while the U/Pb ratio showed 3-24% variations depending on element mass fractions. Using the synthetic calcite as primary RMs, we could date a natural calcite RM, WC-1, with analytical uncertainty as low as 3%. The method presented can be useful to produce calcite with controlled and homogeneous element mass fractions, and is a promising alternative to natural calcite RMs for U-Pb geochronology.

Gamma-ray spectroscopy with a CeBr scintillator under intense -ray fields for nuclear decommissioning

Kaburagi, Masaaki; Shimazoe, Kenji*; Kato, Masahiro*; Kurosawa, Tadahiro*; Kamada, Kei*; Kim, K. J.*; Yoshino, Masao*; Shoji, Yasuhiro*; Yoshikawa, Akira*; Takahashi, Hiroyuki*; et al.

Nuclear Instruments and Methods in Physics Research A, 988, p.164900_1 - 164900_8, 2021/02

https://doi.org/10.1016/j.nima.2020.164900

An increasing number of nuclear facilities have been decommissioned worldwide following the 2011 accident of the TEPCO' Fukushima Daiichi Nuclear Power Station. During the decommissioning, radioactive materials have to be retrieved under proper management. In this study, a small cubic CeBr spectrometer with dimensions of 5 mm 5 mm 5 mm was manufactured to perform -ray spectroscopy under intense -ray fields. Furthermore, thanks to a fast digital process unit and a customized photomultiplier, the device could perform -ray spectroscopy at dose rates of over 1 Sv/h. The energy resolution (FWHM) at 662 keV ranged from 4.4% at 22 mSv/h to 5.2% at 1407 mSv/h for a Cs radiation field. Correspondingly, at 1333 keV, it ranged from 3.1% at 26 mSv/h to 4.2% at 2221 mSv/h for a Co radiation field, which suggested to realize -ray assessment of Cs, Cs, Co, and Eu at dose rates of over 1 Sv/h.

Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor (Contract research); FY2019 Nuclear Energy Science & Technology and Human Resource Development Project

Collaborative Laboratories for Advanced Decommissioning Science; Nagoya University*

JAEA-Review 2020-063, 44 Pages, 2021/01

JAEA-Review-2020-063.pdf:2.55MB

JAEA/CLADS had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project in FY2019. Among the adopted proposals in FY2019, this report summarizes the research results of the "Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor" conducted in FY2019.