Field-Scale Migration of 99Tc and 129I at the Nevada Test Site


The groundwater at the Nevada Test Site (NTS) contains many long-lived radionuclides, including 99Tc (technetium) and 129I (iodine), as a result of 828 underground nuclear weapons tests conducted between 1951 and 1992. We synthesized a body of data collected on the distribution of 99Tc and 129I in groundwater to assess their migration at NTS, at field scales over distances of hundreds of meters and for durations up to forty years and under hydrogeologic conditions very similar to the proposed geological repository at Yucca Mountain. The results of our study show that Tc does not necessarily exist as a mobile and conservative species \({\text{TcO}}_4^ - \), as has been commonly assumed. This conclusion is corroborated by recent in situ redox potential measurements, which show that groundwaters at multiple locations of the NTS are not oxidizing, and mobility of reduced Tc species (TcO2 • nH2O) is greatly decreased. Speciation of iodine and its associated reactivity is also complex in the groundwater at the NTS, and its effect on the mobility of iodine should be the subject of future studies.

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This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. The work is funded through the Science and Technology Program of the Office of Civilian Radioactive Waste Management of the U.S. Department of Energy. The authors thank Timothy Rose, Annie Kersting, Jean Moran, and Karen Rath for stimulating discussions and helpful comments.

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Correspondence to Qinhong Hu.

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Hu, Q., Smith, D.K. Field-Scale Migration of 99Tc and 129I at the Nevada Test Site. MRS Online Proceedings Library 824, 336–341 (2004).

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