Geochemical factors for secondary mineral formation at naturally-occurring hyperalkaline spring in Oman ophiolite

Anraku, Sohtaro; Matsubara, Isamu*; Morimoto, Kazuya*; Sato, Tsutomu*

Nendo Kagaku, 55(2), p.17 - 30, 2017/00

http://doi.org/10.11362/jcssjnendokagaku.55.2_17

Anionic radionuclides are important for the long-term safety assessment of Japanese transuranic (TRU) waste disposal facilities. Degradation of cementitious materials used to construct the TRU waste disposal facilities, however, can produce a hyperalkaline leachate and so it is necessary to understand the reaction mechanisms that will control the behavior and fate of anionic radionuclides under these hyperalkaline conditions. An excellent natural analogue site to study relevant reaction mechanisms is provided in Oman where hyperalkaline spring waters (pH 11) from serpentinized peridotites discharge into moderately alkaline rivers. Aragonite was found in all secondary mineral samples, with accessory minerals of calcite, layered double hydroxide (LDH) and brucite. LDH was observed at the high Al concentration springs and brucite at the low Al concentration springs. Calcite was only found close to the springs. Distal calcite formation was inhibited due to high Mg concentrations in the river water. The spatial distribution of minerals therefore implicates the importance of the mixing ratio of spring to river water and the relative chemical compositions of the spring and river waters. Supporting mixing model calculations could successfully reproduce the precipitation of aragonite and LDH. The observed decrease in Ca concentration could be explained by aragonite precipitation. pH exerted a strong control on the precipitation of LDH and so too, therefore, on Al concentration. In the mixing water experiments containing up to 40% river water, LDH and brucite were both oversaturated, but brucite was not always identified by XRD. The possible inhibition of brucite by LDH precipitation was an unexpected result.

Evaluation of thermal physical properties for fast reactor fuels; Melting point and thermal conductivities

Kato, Masato; Morimoto, Kyoichi; Komeno, Akira; Nakamichi, Shinya; Kashimura, Motoaki; Abe, Tomoyuki; Uno, Hiroki*; Ogasawara, Masahiro*; Tamura, Tetsuya*; Sugata, Hiromasa*; et al.

JAEA-Technology 2006-049, 32 Pages, 2006/10

JAEA-Technology-2006-049.pdf:19.46MB
JAEA-Technology-2006-049(errata).pdf:0.32MB

Japan Atomic Energy Agency has developed a fast breeder reactor(FBR), and plutonium and uranium mixed oxide (MOX) having low density and 20-30%Pu content has used as a fuel of the FBR, Monju. In plutonium, Americium has been accumulated during long-term storage, and Am content will be increasing up to 2-3% in the MOX. It is essential to evaluate the influence of Am content on physical properties of MOX on the development of FBR in the future. In this study melting points and thermal conductivities which are important data on the fuel design were measured systematically in wide range of composition, and the effects of Am accumulated were evaluated. The solidus temperatures of MOX were measured as a function of Pu content, oxygen to metal ratio(O/M) and Am content using thermal arrest technique. The sample was sealed in a tungsten capsule in vacuum for measuring solidus temperature. In the measurements of MOX with Pu content of more than 30%, a rhenium inner capsule was used to prevent the reaction between MOX and tungsten. In the results, it was confirmed that the melting points of MOX decrease with as an increase of Pu content and increase slightly with a decrease of O/M ratio. The effect of Am content on the fuel design was negligible small in the range of Am content up to 3%. Thermal conductivities of MOX were evaluated from thermal diffusivity measured by laser flash method and heat capacity calculated by Nuemann- Kopp's law. The thermal conductivity of MOX decreased slightly in the temperature of less than 1173K with increasing Am content. The effect of Am accumulated in long-term storage fuel was evaluated from melting points and thermal conductivities measured in this study. It is concluded that the increase of Am in the fuel barely affect the fuel design in the range of less than 3%Am content.

Thermal conductivity measurement of (Pu,Am)O (x=0.03, 0.07)

Matsumoto, Taku*; Arima, Tatsumi*; Inagaki, Yaohiro*; Idemitsu, Kazuya*; Kato, Masato; Morimoto, Kyoichi; Ogasawara, Masahiro*

no journal, , 

Development of minor actinide (MA) bearing MOX fuels has been advanced to reduce high level waste. In the development of such new type fuels, it is important to understand physical properties. The thermal conductivity is one of the important properties for development of the fuels, and effect of PuO and AmO content on thermal conductivity was investigated. A few thermal conductivity of PuO were reported previously, which differ widely in the measured data. The data of Am-containing MOX were also measured, but the effect of Am was unclear because of low Am content. In the present work, thermal conductivity of (Pu,Am)O was measured, and the effect of Am content was evaluated to contribute to analyze thermal conductivity of MA-bearing oxide fuels.

Measurement of oxygen potential in (PuAm)O

Matsumoto, Taku; Arima, Tatsumi*; Inagaki, Yaohiro*; Idemitsu, Kazuya*; Kato, Masato; Morimoto, Kyoichi; Sunaoshi, Takeo*

no journal, , 

no abstracts in English

Inter-diffusion study of actinides in a MOX diffusion couple

Matsumoto, Taku; Arima, Tatsumi*; Inagaki, Yaohiro*; Idemitsu, Kazuya*; Kato, Masato; Morimoto, Kyoichi; Uno, Hiroki*; Tamura, Tetsuya*

no journal, , 

O/M ratio dependence of inter-diffusion coefficient of U and Pu at 1873 K was evaluated from MOX and UO diffusion couple. The diffusion coefficient at O/M = 2.00 was about two orders of magnitude greater than that at O/M = 1.96. In addition, it was observed that grain boundary diffusion is so large compared to bulk one for O/M = 2.00. On the other hand, GB and bulk diffusions were not clearly observed for O/M = 1.96.

Synthesis and Cs-adsorption behavior of phyllosilicates in saponite-phlogopite system

Yamada, Hirohisa*; Yokoyama, Shingo*; Watanabe, Yujiro*; Morimoto, Kazuya*; Suzuki, Shinichi; Yaita, Tsuyoshi; Hatta, Tamao*

no journal, ,