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Technetium Getters to Improve Cast Stone Performance

Published online by Cambridge University Press:  23 March 2015

James J. Neeway ,
Amanda R. Lawter ,
R. Jeffrey Serne ,
R. Matthew Asmussen  and
Nikolla P. Qafoku
James J. Neeway
Affiliation:
Pacific Northwest National Laboratory, Energy and Environment Directorate Richland, WA 99352, U.S.A.
Amanda R. Lawter
Affiliation:
Pacific Northwest National Laboratory, Energy and Environment Directorate Richland, WA 99352, U.S.A.
R. Jeffrey Serne
Affiliation:
Pacific Northwest National Laboratory, Energy and Environment Directorate Richland, WA 99352, U.S.A.
R. Matthew Asmussen
Affiliation:
Pacific Northwest National Laboratory, Energy and Environment Directorate Richland, WA 99352, U.S.A.
Nikolla P. Qafoku
Affiliation:
Pacific Northwest National Laboratory, Energy and Environment Directorate Richland, WA 99352, U.S.A.
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Abstract

A cementitious waste form known as Cast Stone is the baseline waste form for solidification of aqueous secondary wastes, including Hanford Tank Waste Treatment and Immobilization Plant (WTP) secondary liquid effluents to be treated and solidified at the Hanford Site Effluent Treatment Facility. Cast Stone is also being evaluated as a possible supplemental immobilization technology to provide the necessary low activity waste (LAW) treatment capacity to complete the Hanford tank waste cleanup mission in a timely and cost effective manner. Two radionuclides of particular concern in these waste streams are technetium-99 (99Tc) and iodine-129 (129I). These radioactive tank waste components are predicted to contribute the most risk to groundwater – the most probable pathway for future environmental impacts associated with the cleanup of the Hanford site. A recent environmental assessment of Cast Stone performance, which assumes a diffusion controlled release of contaminants from the waste form, calculates groundwater in excess of the allowable maximum permissible concentrations for both contaminants. There is, therefore, a need and an opportunity to improve the retention of both 99Tc and 129I in Cast Stone. One method to improve the performance of Cast Stone is through the addition of “getters” that selectively sequester Tc and I, therefore reducing their diffusion out of Cast Stone. In this paper, we present results of Tc and I removal from solution with various getters. Batch sorption experiments were conducted with deionized water (DIW) and a highly caustic LAW simulant with a 7.8 M average Na concentration. In general, the data show that the selected getters are effective in DIW but their performance is compromised when experiments are performed with the 7.8 M Na Ave LAW simulant. The diminished performance in the LAW simulant may be due to competition with Cr present in the 7.8 M Na Ave LAW simulant and to a pH effect that may create a negatively charged surface that can repel negatively charged species.

Keywords

waste managementadditivesscanning electron microscopy (SEM)
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1744: Symposium EE – Scientific Basis for Nuclear Waste Management XXXVIII , 2015 , pp. 43 - 52
Copyright
Copyright © Materials Research Society 2015 

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References

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