Distribution of 99Tc and 129I in the vicinity of underground nuclear tests at the Nevada Test Site

Abstract

99 Tc and 129 I are important contributors to risk assessment due to their long halflives and high mobility as aqueous anionic species. We analyzed 99 Tc and 129 I in groundwater samples in and near 11 underground nuclear tests and in melt glass and rock samples retrieved from the Chancellor test cavity, Nevada Test Site. The 129 I/ 127 I ratio ranges from 10 -3 to 10 -6 in cavity water and 10 -4 to 10 -9 in satellite wells. The 99 Tc concentration ranges from 3 to 10 -4 Bq/L in cavity waters and from 0.3 to 10 -4 Bq/L in satellite wells. Downstream migration is apparent for both radionuclides. However, it is affected by both retardation and initial distribution. In-situ 99 Tc and 129 I K d s calculated using rubble and water concentrations are 3 to 22 mL/g and 0 to 0.12 mL/g, respectively and are suggestive of mildly reducing conditions. 129 I distribution in the melt glass, rubble and groundwater of the Chancellor test cavity is 28%, 24% and 48%, respectively; for 99 Tc, it is 65%, 35% and 0.3%, respectively. Our partitioning estimates differ from those of underground tests in French Polynesia, implying that fission product distribution may vary from test to test. Factors that may influence this distribution include geologic conditions (e.g. lithology, water and CO 2 content) and the cooling history of the test cavity.

Determination of technetium-99 in environmental samples: A review

“…23 Before further chemical separation, 99 Tc should be released from the sample matrices into solution. Two common techniques for releasing 99 Tc from solid samples after ashing are acid leaching [8,11,12,82] and alkali fusion [17,[87][88][89]. Concentrated HNO 3 [6,90] 99 Tc and 2 h are necessary to release 99 Tc from sample matrices.…”

“…Alkali fusion is a method for complete decomposition of solid samples, especially soil, sediment and rocks. A mixture of Na 2 O 2 and carbonate-free NaOH was often used as fusion reagents for the decomposition of solid samples at 400 0 C-700 0 C [17,88,89]. The fusion cake is dissolved with water or diluted acid solution prior to isolation 24 of 99 Tc.…”

“…ICP-MS is a relatively powerful technique which has been extensively utilized to determine 99 Tc in environmental samples [18][19][20][21]75,88,[120][121][122]. Compared with β-counting, ICP-MS possesses evident advantages including short analytical time (usually several minutes per sample) and relatively high sensitivity.…”

Neptunium Transport Behavior in the Vicinity of Underground Nuclear Tests at the Nevada Test Site

“…Even if the initial distribution of Np is similar, if not the same, as Pu, the former radionuclide tends to become pentavalent and mobile as it migrates away from its origins over time (Lindahl et al 2004& 2005, Novikov et al 2009). The groundwater conditions in NNSS hot wells are relatively isolated and the redox conditions can vary (Hu et al 2008, Nimz andThompson 1992). As a result, oxidizing conditions cannot be assumed for all NNSS groundwaters.…”

Measurement of I-129 in environmental samples by ICP-CRI-QMS: possibilities and limitations

“…The concerns either in radiation protection [1][2][3][4][5][6] or in scientific research [4,[7][8][9][10] highlight the necessity of a suitable technique for 129 I analysis. The big challenge in the investigation of 129 I in the environment comes from the low concentration of 129 I in the environmental samples and its long half-life, which make it difficult to be determined either by mass spectrometry or by a radioactivity decay measurement.…”