Migration of Technetium-99 in the Alluvial Aquifer at the Nevada Test Site, Nevada

Abstract

Radionuclide migration / Technetium-99 / Relative migration rates SummaryThe Cambric Experiment, under the auspices of the Hydrology/ Radionuclide Migration Project, is measuring the migration of radionuclides from the site of an old underground nuclear test. Ten years after the 1965 test, a re-entry well (RNM-1) was drilled into the remnant of the explosion cavity to obtain core and water samples. Pumping water from a satellite well (RNM-2S) 91 m from the cavity subsequently induced an artificial gradient that has allowed soluble radionuclides to migrate from the cavity. Tritium (HTO) has been observed in the RNM-2S water; its elution has been well characterized. Other radionuclides have also been monitored in water from RNM-2S: 36 C1, 85 Kr, l29 I, and 106 Ru. We have recently measured "Tc at the 10-20 fg/1 level in RNM-2S water. In contrast to the 3 H source term, which is essentially entirely available to transport, these results indicate that only ~0.01 % of the "Tc has escaped from the vitrified rock matrix into the water. The technetium in solution appears to be migrating more slowly than the 36 C1 is. Although "Tc's initial breakthrough is similar to that for 3 H, the migration rate of the "Tc center of mass appears to slightly exceed that of 3 H, perhaps as a result of anion exclusion effects. All measured "Tc concentrations are considerably below limits established for public drinking water.

Vadose Zone Transport Field Study: Summary Report

“…Under oxidizing conditions, 99 Tc exists as the soluble heptavalent pertechnetate ion, TcO 4 -which is highly mobile in soils and groundwater. Measurements in a wide range of soils, including alluvium, suggest that TcO 4 -also exhibits anion exclusion effects (Lieser and Bauscher 1987;Zhuang et al 1988;Schroeder et al 1993). Neglecting this mechanism could result in overestimating vadose zone water flux and recharge rates to the groundwater based on chloride mass balance, underestimating the impact of colloids, and underestimating the migration rates of high-risk contaminants like 99 Tc.…”

Technetium measurements by accelerator mass spectrometry at LLNL

“…This radionuclide is a weak beta emitter which is difficult to measure at low levels by decay counting methods. A number of mass spectrometric methods have been developed to address needs for low-level 99 Tc measurements, including thermal ionization mass spectrometry (TIMS), [1][2][3] inductively-coupled plasma mass spectrometry (ICP-MS), [4][5][6] resonance ionization mass spectrometry (RIMS). 7,8 More recently, the feasibility of accelerator mass spectrometry (AMS) for 99 Tc measurements has been demonstrated.…”

Determination of technetium-99 in environmental samples: A review

“…With the advantages of high sensitivity and short analysis time, MS has been applied in many areas and studied extensively, in recent years for measurement of 99 Tc, especially in low level environmental samples [14][15][16][17][18][19][20][21]112,[117][118][119]]. The first trace-level analysis of 99 Tc using MS was reported by Anderson et al [87].…”

“…Since then, extensive measurement of 99 Tc has been carried out using this technique. So far, several MS techniques, including AMS [14][15][16], RIMS [112,117], TIMS [17,118,119], and the popular ICP-MS [18][19][20][21], have been introduced to determine the concentration of 99 Tc.…”

“…Thermal ionization mass spectrometry (TIMS) and resonance ionization mass spectrometry (RIMS) are two of the more important of these [17,112,[117][118][119]. TIMS with multiple ion collectors is generally the method of choice for isotope ratio measurements with high precision (down to 0.002 %).…”