Field-Scale Migration of 99Tc and 1291 at the Nevada Test Site

摘要

The groundwater at the Nevada Test Site (NTS) contains many long-lived radionuclides, including (sup 99)TC (technetium) and (sup 129)I (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 (sup 99)Tc and (sup 129)I 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 TcO(sub 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 (TcO(sub 2) - 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.