Glenn T. Seaborg Institute, Physical & Life Sciences , Lawrence Livermore National Laboratory , Livermore , California 94550 , United States.
Environ Sci Technol. 2019 Jul 2;53(13):7363-7370. doi: 10.1021/acs.est.8b07199. Epub 2019 Jun 21.
Approximately 2.8 t of plutonium (Pu) has been deposited in the Nevada National Security Site (NNSS) subsurface as a result of underground nuclear testing. Most of this Pu is sequestered in nuclear melt glass. However, Pu migration has been observed and attributed to colloid facilitated transport. To identify the mechanisms controlling Pu mobilization, long-term (∼3 year) laboratory nuclear melt glass alteration experiments were performed at 25 to 200 °C to mimic hydrothermal conditions in the vicinity of underground nuclear tests. The clay and zeolite colloids produced in these experiments are similar to those identified in NNSS groundwater. At 200 °C, maximum Pu and colloid concentrations of 30 Bq/L and 150 mg/L, respectively, were observed. However, much lower Pu and colloid concentrations were observed at 25 and 80 °C. These data suggest that Pu concentrations above the drinking water Maximum Contaminant Levels (0.56 Bq/L) may exist during early hydrothermal conditions in the vicinity of underground nuclear tests. However, formation of colloid-associated Pu will tend to decrease with time as nuclear test cavity temperatures decrease. Furthermore, median colloid concentrations in NNSS groundwater (1.8 mg/L) suggest that the high colloid and Pu concentrations observed in our 140 and 200 °C experiments are unlikely to persist in downgradient NNSS groundwater. While our experiments did not span all groundwater and nuclear melt glass conditions that may be present at the NNSS, our results are consistent with the documented low Pu concentrations in NNSS groundwater.
由于地下核试验，大约有 2.8 吨钚（Pu）沉积在内华达国家安全场址（NNSS）地下。这些 Pu 中的大部分被隔离在核熔融玻璃中。然而，已经观察到 Pu 的迁移，并归因于胶体促进的传输。为了确定控制 Pu 动员的机制，在 25 至 200°C 的温度下进行了长达 3 年的实验室核熔融玻璃变化实验，以模拟地下核试验附近的热液条件。在这些实验中产生的粘土和沸石胶体与在 NNSS 地下水中鉴定出的胶体相似。在 200°C 时，观察到最大 Pu 和胶体浓度分别为 30 Bq/L 和 150 mg/L。然而，在 25°C 和 80°C 时观察到的 Pu 和胶体浓度要低得多。这些数据表明，在地下核试验附近的早期热液条件下，Pu 浓度可能超过饮用水最大污染物水平（0.56 Bq/L）。然而，随着核试验腔温度的降低，胶体结合的 Pu 的形成将趋于减少。此外，NNSS 地下水中的胶体浓度中位数（1.8 mg/L）表明，在我们的 140°C 和 200°C 实验中观察到的高胶体和 Pu 浓度不太可能在向下游的 NNSS 地下水中持续存在。虽然我们的实验没有涵盖可能存在于 NNSS 的所有地下水和核熔融玻璃条件，但我们的结果与 NNSS 地下水中记录的低 Pu 浓度一致。
