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Effects of hydrosulfide and pH on iodine release from an alumina matrix solid confining silver iodide

Published online by Cambridge University Press:  07 May 2015

Tomofumi Sakuragi ,
Satoshi Yoshida ,
Osamu Kato  and
Kaoru Masuda
Tomofumi Sakuragi
Affiliation:
Repository Engineering and EBS Technology Research Project, Radioactive Waste Management Funding and Research Center, Tsukishima 1-15-7, Chuo City, Tokyo, Japan
Satoshi Yoshida
Affiliation:
Repository Engineering and EBS Technology Research Project, Radioactive Waste Management Funding and Research Center, Tsukishima 1-15-7, Chuo City, Tokyo, Japan
Osamu Kato
Affiliation:
Kobe Steel, Ltd., Wakinohama-Kaigandori 2-2-4, Chuo-ku, Kobe, Japan
Kaoru Masuda
Affiliation:
Kobelco Research Institute, Inc., Takatsukadai 1-5-5, Nishi-ku, Kobe, Japan
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Abstract

Alumina matrix solidification is a hot isostatic pressing (HIP) technique used to immobilize radioactive iodine (129I) in the form of silver iodide. In the present study, an alumina matrix solidification sample with a porosity of 12.9% was obtained by performing HIP at 175 MPa and 1200°C for 3 hours on a simulated spent silver-sorbent saturated with stable iodine. Material Characterization Centre-1 (MCC-1) leaching tests for the simulated waste form were performed using hydrosulfide (HS-) as a reductant at concentrations ranging from 3 × 10-7 M to 3 × 10-3 M and at pH values ranging from 8.0 to 12.5. Leached iodine concentrations were below the detection limit for ICP-MS measurements at HS- concentrations of 3 × 10-7 M and 3 × 10-5 M. This result was due to the stability of AgI. At an HS- concentration of 3 × 10-3 M, iodine leaching rapidly increased within 10 days. The maximum iodine concentration in the solution was 4.33 × 10-3 M, which corresponds to 85% dissolution of the initial iodine. This value was measured after 552 days under an HS- concentration of 3 × 10-3 M at pH 11. An analysis of specimen cross-sections suggested the following reaction: 2AgI + HS- = Ag2S + 2I- + H+. The pH affected matrix aluminum dissolution but did not significantly affect the iodine leaching behavior. Furthermore, the normalized mass loss of iodine was larger than that of aluminum by a factor greater than 104, which is due to the large porosity and the dissolution of interior AgI of the solid.

Keywords

hot isostatic pressing (HIP)Inuclear materials
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1744: Symposium EE – Scientific Basis for Nuclear Waste Management XXXVIII , 2015 , pp. 21 - 28
Copyright
Copyright © Materials Research Society 2015 

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References

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