Sassi Michel, Okumura Masahiko, Machida Masahiko, Rosso Kevin M
Physical Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99354, USA.
Phys Chem Chem Phys. 2017 Oct 11;19(39):27007-27014. doi: 10.1039/c7cp04496h.
The accidental release and incorporation of radiocesium into soil minerals represents a massive environmental, technical and social challenge. Accurately forecasting the evolving distribution and fate of long- and medium-lived isotopes such as Cs and Cs over decadal time scales is essential. The cesium cation has long been modeled as a strongly and selectively sorbed species into clay mineral interlayers; however, because of the time scales involved by the radioisotopes half-lives, the effects of radioactive decay on Cs retention have been unknown. We report density functional theory (DFT) simulations of transmutation effects of radiocesium on long-term Cs retention in phlogopite. The calculations show that the progressive appearance of daughter product Ba is accompanied by a proportional increase in thermodynamic driving force to preferentially discharge remaining Cs, both radioactive and stable, back into aqueous solution. Based on thermodynamic analysis, the findings indicate that radiocesium transmutation provides a mean to weaken the binding of Cs in phyllosilicate minerals, therefore potentially involving a premature re-release of Cs back into the environment. In the case where radiogenic Ba ions accumulate in the mineral, collateral effects would ultimately be an increase in the overall interlayer binding energy and a lower resorption capacity.
放射性铯意外释放并掺入土壤矿物质中是一项巨大的环境、技术和社会挑战。准确预测铯-137和铯-134等长寿命和中寿命同位素在数十年时间尺度上不断变化的分布和归宿至关重要。长期以来，铯阳离子一直被模拟为强烈且选择性地吸附在粘土矿物层间的物种；然而，由于放射性同位素半衰期所涉及的时间尺度，放射性衰变对铯保留的影响一直未知。我们报告了放射性铯嬗变对金云母中长期铯保留影响的密度泛函理论（DFT）模拟。计算结果表明，子产物钡的逐渐出现伴随着热力学驱动力的相应增加，促使剩余的放射性铯和稳定铯优先释放回水溶液中。基于热力学分析，研究结果表明放射性铯嬗变提供了一种削弱铯在层状硅酸盐矿物中结合力的方式，因此可能导致铯过早地重新释放回环境中。在矿物中放射性成因钡离子积累的情况下，附带效应最终将是层间总结合能增加和再吸附能力降低。
