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Development of the Synthetic Rock Technique for the Immobilization of Iodine: Kinetics of the Alumina Matrix Dissolution under High Alkaline Conditions

Published online by Cambridge University Press:  07 January 2013

Hideaki Miyakawa ,
Tomofumi Sakuragi ,
Hitoshi Owada ,
Osamu Kato  and
Kaoru Masuda
Hideaki Miyakawa
Affiliation:
Radioactive Waste Management Funding and Research Center, 1-15-7, Tsukishima, Chuo-ku, Tokyo 104-0052, Japan.
Tomofumi Sakuragi
Affiliation:
Radioactive Waste Management Funding and Research Center, 1-15-7, Tsukishima, Chuo-ku, Tokyo 104-0052, Japan.
Hitoshi Owada
Affiliation:
Radioactive Waste Management Funding and Research Center, 1-15-7, Tsukishima, Chuo-ku, Tokyo 104-0052, Japan.
Osamu Kato
Affiliation:
Kobe Steel Ltd., 4-2-7, Iwaya-Nakamachi, Nada-ku, Kobe 657-0845, Japan.
Kaoru Masuda
Affiliation:
Kobelco Research Institute Inc., 1-5-5, Takatsukadai, Nishi-ku, Kobe 651-2271, Japan.
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Abstract

Iodine filters expended after nuclear fuel reprocessing contain radioactive iodine (I-129), almost all of which exists as silver iodide (AgI). The synthetic rock technique is a solidification treatment technique using hot isostatic press (HIP), in which the alumina adsorbent base material is synthesized to form a dense solidified material (synthetic rock), and I-129 is physically confined in the form of AgI in the alumina matrix. Thus, it is necessary to understand the matrix dissolution behavior to evaluate the iodine release behavior.

Experiments involving the dissolution of the matrix were carried out under various temperatures (35–70 °C) and pH values (10–12.5) that reflect the disposal conditions. The results of the experiments showed that the dissolution rate of Al visibly increases with temperature and pH. The dissolution rate constant was calculated from the initial data assuming the dissolution of the matrix as a primary reaction. The logarithmic rate constant showed a good linear correlation with the pH and the reciprocal of temperature. The 27Al-NMR analysis of the solutions of the dissolved matrix showed that the major chemical species present in the solutions was Al(OH)4-. This indicated that the dissolution of the matrix can be described by the following equation: Al2O3 + 2OH- + 3H2O → 2Al(OH)4-. Subsequently, the empirical equation of the rate of dissolution of the matrix as a function of the temperature and pH was derived. It will be used to evaluate the iodine release behavior from the synthetic rock.

Keywords

waste managementhot isostatic pressing (HIP)I
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1518: Symposium LL – Scientific Basis for Nuclear Waste Management XXXVI , 2012 , pp. 79 - 84
Copyright
Copyright © Materials Research Society 2012 

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References

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