Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87507, United States.
Department of Environmental Health and Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, United States.
Environ Sci Technol. 2024 Oct 22;58(42):18903-18914. doi: 10.1021/acs.est.4c04048. Epub 2024 Oct 4.
The detection of noble gas radioisotopes following a suspected underground nuclear explosion is the surest indicator that nuclear detonation has occurred. However, the accurate interpretation and attribution of radioisotopic signatures is only possible with a complete understanding of transport processes occurring between the nuclear cavity and surface. In the far-field, diffusive forces contributing to gas transport are impacted by temperature gradients and subsurface lithology. In the current study, we investigate diffusive transport of xenon (Xe), krypton (Kr), and sulfur hexafluoride (SF) through intact Bandelier tuff at elevated temperatures using a newly developed high temperature diffusion cell. Diffusion coefficients determined using Finite Element Heat and Mass transfer code simulations and the Parameter ESTimation tool range from 2.6-3.1 × 10 m/s at 20 °C, 3.4-5.1 × 10 m/s at 40 °C, and 4.3-7.0 × 10 m/s at 70 °C. Sorption was found to be an important transport mechanism at ambient temperatures (20 °C). Most critically, our study shows that empirical porosity-based diffusion estimates for these gases through tuff captured neither the magnitude nor trends relative to a nonsorbing sandstone. These new insights highlight the importance of experimental transport investigations and will be used to improve models for subsurface gas propagation relevant to proliferation detection and environmental contamination.
检测疑似地下核爆炸后产生的稀有气体放射性同位素是核爆炸发生的确切指标。然而，只有在完全了解核空腔与地表之间发生的传输过程的情况下，才能对放射性同位素特征进行准确的解释和归因。在远场中，对气体传输有贡献的扩散力受温度梯度和地下岩性的影响。在当前的研究中，我们使用新开发的高温扩散池，在高温下研究氙（Xe）、氪（Kr）和六氟化硫（SF）通过完整的斑脱土的扩散传输。使用有限元热和质量转移代码模拟和参数估计工具确定的扩散系数在 20°C 时为 2.6-3.1×10m/s，在 40°C 时为 3.4-5.1×10m/s，在 70°C 时为 4.3-7.0×10m/s。发现吸附是环境温度（20°C）下的一种重要传输机制。最重要的是，我们的研究表明，基于经验孔隙率的这些气体通过斑脱土的扩散估计既没有捕捉到与非吸附砂岩相比的量级，也没有捕捉到趋势。这些新的见解强调了进行实验传输研究的重要性，并将用于改进与增殖检测和环境污染有关的地下气体传播模型。
