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Effect of pH on Plutonium Migration Behavior in Compacted Bentonite

Published online by Cambridge University Press:  16 February 2017

Ryo Hamada ,
Noriyuki Maeda ,
Kazuya Idemitsu ,
Yaohiro Inagaki ,
Tatsumi Arima ,
Daisuke Akiyama ,
Kenji Konashi ,
Makoto Watanabe  and
Shin-ichi Koyama
Ryo Hamada
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., 744 Motooka, Nishi-ku, Fukuoka, Japan
Noriyuki Maeda
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., 744 Motooka, Nishi-ku, Fukuoka, Japan
Kazuya Idemitsu*
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., 744 Motooka, Nishi-ku, Fukuoka, Japan
Yaohiro Inagaki
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., 744 Motooka, Nishi-ku, Fukuoka, Japan
Tatsumi Arima
Affiliation:
Dept. of Applied Quantum Physics and Nuclear Engineering, Kyushu Univ., 744 Motooka, Nishi-ku, Fukuoka, Japan
Daisuke Akiyama
Affiliation:
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 1-1 Katahira, 2-choume, Aoba-ku,Sendai, Japan
Kenji Konashi
Affiliation:
International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, 2145-2 Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki, Japan
Makoto Watanabe
Affiliation:
International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University, 2145-2 Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki, Japan
Shin-ichi Koyama
Affiliation:
Japan Atomic Energy Agency, 4002 Narita, Oarai, Higashi-Ibaraki, Ibaraki, Japan
*
*(Email: idemitsu@nucl.kyushu-u.ac.jp)
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Abstract

In disposing of high-level radioactive waste, the drop in pH in the repository as the iron overpack corrodes must be considered. Plutonium migration behavior may be affected by the pH of pore water in compacted bentonite barriers in high-level waste repositories. To examine the effect of pH on migration behavior, H-bentonite was prepared by treating Japanese Na-bentonite, Kunipia-F, with hydrochloric acid. Diffusion experiments were performed with mixtures of Na- and H-bentonites. The pH value in the pore water of the water-saturated bentonite mixtures decreased from 8 to 3 as the mixing ratio of H-bentonite increased. Diffusion experiments were carried out by using 238Pu then apparent diffusion coefficients were determined from the plutonium distribution in the specimens. The apparent diffusion coefficients were on the order of 10-13 to 10-12 m2/s at pH values lower than 4, whereas they were less than 10-14 m2/s at pH values higher than 6.5. These results indicate that plutonium diffused faster as Pu3+ or PuO22+ due to disproportionation at lower pH while plutonium could be retarded as Pu(OH)40 by sorption on bentonite at higher pH.

Keywords

DiffusionPuwaste management
Type
Articles
Information
MRS Advances , Volume 1 , Issue 61: Scientific Basis for Nuclear Waste Management XXXIX , 2016 , pp. 4011 - 4017
Copyright
Copyright © Materials Research Society 2017 

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References

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