Field-scale model for the natural attenuation of uranium at the Hanford 300 Area using high-performance computing
Field-scale model for the natural attenuation of uranium at the Hanford 300 Area using high-performance computing
复制标题
DOI：
10.1029/2009wr008819
复制
发表时间：
2010-09-22
影响因子：
5.4
通讯作者：
Lichtner, Peter C.
中科院分区：
文献类型：
--
作者：
Hammond, Glenn E.;Lichtner, Peter C.
高分辨率，三维，反应流和运输模拟进行描述迁移的六价铀[U（VI）]在汉福德300区接壤的哥伦比亚河，并更好地了解持久性的铀羽在现场。在美国能源部SciDAC-2项目下开发的计算机代码PFLOTRAN用于在ORNL的Cray XT 4/XT 5超级计算机Jaguar上执行的模拟。在模拟中使用的概念模型是基于三个不同的阶段或时间段的U（VI）羽流的演变的认识。这些对应于：（1）初始废物就位;（2）初始存在不稳定和不稳定U（VI），演化U（VI）羽流从源区延伸到河流边界，代表当今条件;（3）包气带中所有不稳定U（VI）和不稳定U（VI）的完全清除。这项工作主要集中在模拟第二阶段使用平衡和多速率吸附模型不稳定的U（VI）和一个连续的来源释放的不稳定的U（VI）在南工艺池通过溶解的变斑铜矿作为替代矿物。对于这种情况下，哥伦比亚河水位的快速波动与不稳定铀（VI）的缓慢释放相结合的污染沉积物中被发现发挥主导作用，在确定U（VI）的迁移行为与吸附只有二级效应。然而，多速率模型是必不可少的，在解释突破曲线从实验室柱实验使用相同的沉积物，并证明是重要的第三阶段。计算表明，U（VI）排放到河流中的高度波动率在棘轮状行为作为河流水位上升和福尔斯。在计算河流边界处U（VI）通量时，必须在模型中解决高频波动问题。通过对瞬时通量进行时间平均来平均叠加在河流水位波动上的噪声，发现到河流的累积U（VI）通量随时间近似线性地增加。流速和U（VI）通量是高度敏感的电导边界条件，描述河流-沉积物界面。通过调整电导系数，使之更好地匹配所测得的测压头，获得了良好的协议与现场研究的平均水通量10（9）公斤/年和U（VI）的25公斤/年的河流含水层边界的计算域包括南工艺池塘。最后，它表明，通过全球质量守恒，从源区的U（VI）浸出率有关的U（VI）通量在河流边界。
High-resolution, three-dimensional, reactive flow and transport simulations are carried out to describe the migration of hexavalent uranium [U(VI)] at the Hanford 300 Area bordering the Columbia River and to better understand the persistence of the uranium plume at the site. The computer code PFLOTRAN developed under a DOE SciDAC-2 project is employed in the simulations that are executed on ORNL's Cray XT4/XT5 supercomputer Jaguar. The conceptual model used in the simulations is based on the recognition of three distinct phases or time periods in the evolution of the U(VI) plume. These correspond to (1) initial waste emplacement; (2) initial presence of both labile and nonlabile U(VI) with an evolved U(VI) plume extending from the source region to the river boundary, representing present-day conditions; and (3) the complete removal of all nonlabile U(VI) and labile U(VI) in the vadose zone. This work focuses primarily on modeling Phase II using equilibrium and multirate sorption models for labile U(VI) and a continuous source release of nonlabile U(VI) in the South Process Pond through dissolution of metatorbernite as a surrogate mineral. For this case, rapid fluctuations in the Columbia River stage combined with the slow release of nonlabile U(VI) from contaminated sediment are found to play a predominant role in determining the migration behavior of U(VI) with sorption only a second-order effect. Nevertheless, a multirate model was essential in explaining breakthrough curves obtained from laboratory column experiments using the same sediment and is demonstrated to be important in Phase III. The calculations demonstrate that U(VI) is discharged to the river at a highly fluctuating rate in a ratchet-like behavior as the river stage rises and falls. The high-frequency fluctuations must be resolved in the model to calculate the flux of U(VI) at the river boundary. By time averaging the instantaneous flux to average out noise superimposed on the river stage fluctuations, the cumulative U(VI) flux to the river is found to increase approximately linearly with time. The flow rate and U(VI) flux are highly sensitive to the conductance boundary condition that describes the river-sediment interface. By adjusting the conductance coefficient to give a better match to the measured piezometric head, good agreement was obtained with field studies for both the mean flux of water of 10(9) kg/yr and U(VI) of 25 kg/yr at the river-aquifer boundary for a computational domain encompassing the South Process Pond. Finally, it is demonstrated that, through global mass conservation, the U(VI) leach rate from the source region is related to the U(VI) flux at the river boundary.