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Tc Behavior in the Basalt-Synthetic Groundwater System as a Function of Temperature and Initial Oxygen Content

Published online by Cambridge University Press:  28 February 2011

M. I. Wood ,
L. L. Ames  and
J. E. Mcgarrah
M. I. Wood
Affiliation:
Rockwell Hanford Operations, P. 0. Box 800, Richland, Washington 99352
L. L. Ames
Affiliation:
Pacific Northwest Laboratory, P. 0. Box 899, Richland, Washington 99352
J. E. Mcgarrah
Affiliation:
Pacific Northwest Laboratory, P. 0. Box 899, Richland, Washington 99352
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Abstract

Experiments have been completed in the basalt-Tc-doped groundwater sys- tem to quantify the mobility of Tc in the waste package and near field envion- ment in a repository located in basalt. The experiments were completed using a batch sorption technique in which 8 rushed basalt and Tc-doped groundwater were reacted at 85, 100, 125 and 150 °C for periods of time up to 118 days. The water to rock ratio was 10:1 ml/g. In another set of experiments, basalt crushed under anoxic conditions and Tc-doped groundwater were reacted at 85°C at different water to rock ratios (10:3, 20:3, 40:3 and 80:3 ml/g).

The rate and percentage of Tc removed from solution increased with increasing temperature and decreasing water to rock ratio. Also, basalt crushed under anoxic conditions removed >87% of Tc from solution at 85°C in 7 days while no Tc was removed from solution with basalt crushed in air at the same temperature after 118 days. These results are consistent with the hypothesis that (1) ferrous iron in basalt phases preferentially consumes oxygen and will not reduce Tcuntil all free oxygen in the system is consumed. Once oxygen is consumed, reduction of Tc is quite rapid. These data indicate that the potential exists in a basalt hydrothermal environment to satisfactorily immobilize Tc. Reliable application of these data will depend on experimental and theoretical estimates of oxygen consumption with time in the waste package environment following repository closure, subsequent saturation and long term hydrothermal reactions.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 84: Symposium L – Scientific Basis for Nuclear Waste Management X , 1986 , 695
Copyright
Copyright © Materials Research Society 1987

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References

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