Hosseinpour Khanmiri Mohammad
Nuclear Fuel Cycle Research School, Nuclear Science and Technology Research Institute, AEOI, Tehran, 14893-836, Iran.
Sci Rep. 2025 Aug 25;15(1):31314. doi: 10.1038/s41598-025-16532-1.
The superior efficacy of synroc as an immobilization matrix for actinides in spent nuclear fuel has been extensively validated, positioning it as a leading candidate for long-term nuclear waste management. In this context, isotopic investigations of natural analogues are indispensable for optimizing synroc formulations, particularly regarding their capacity to incorporate and retain actinides and their decay products over geological timescales. In this study, a naturally occurring member of the pyrochlore supergroup was identified as betafite through integrated SEM, EMPA, and XRD analyses. The isotopic behavior of uranium was investigated by comparing the activity ratios of parent (U) and daughter (U) nuclides within U(IV) and U(VI) enriched forms of the mineral, formed and preserved over approximately 2 billion years. The U/U activity ratios, 1.089 ± 0.016 in U(IV) forms and 0.956 ± 0.007 in U(VI) forms, demonstrate a preferential accumulation of radiogenic U in the tetravalent uranium sites. Based on the obtained findings, this may indicate a structural affinity and retention capacity of U(IV) for daughter isotopes, which might contribute to its stability under reducing conditions; however, further investigation is required to evaluate its long-term implications. Moreover, dissolution features and redox partitioning indicate that approximately 33% of U(IV) in the system results from the disproportionation of intermediate U(V), highlighting a critical redox transformation pathway relevant to actinide immobilization. These findings underscore the importance of redox-sensitive behavior and uranium isotope fractionation in pyrochlore-group minerals and reinforce the relevance of natural analogues in tailoring synroc compositions. Such analogues serve as empirical benchmarks for predicting the performance of actinide-bearing phases in nuclear waste repositories over geologic timescales.
合成岩石（Synroc）作为乏核燃料中锕系元素固定基质的卓越功效已得到广泛验证，使其成为长期核废料管理的主要候选物。在此背景下，对天然类似物进行同位素研究对于优化合成岩石配方不可或缺，特别是在其在地质时间尺度上纳入和保留锕系元素及其衰变产物的能力方面。在本研究中，通过综合扫描电子显微镜（SEM）、电子探针微分析（EMPA）和X射线衍射（XRD）分析，将一种天然存在的烧绿石超群成员鉴定为贝塔石。通过比较在大约20亿年形成并保存的该矿物富含U(IV)和U(VI)形式中母体（U）和子体（U）核素的活度比，研究了铀的同位素行为。U(IV)形式的U/U活度比为1.089±0.016，U(VI)形式的为0.956±0.007，这表明放射性U在四价铀位点优先积累。基于所得结果，这可能表明U(IV)对子体同位素具有结构亲和力和保留能力，这可能有助于其在还原条件下的稳定性；然而，需要进一步研究以评估其长期影响。此外，溶解特征和氧化还原分配表明，体系中约33%的U(IV)来自中间价态U(V)的歧化反应，突出了与锕系元素固定相关的关键氧化还原转化途径。这些发现强调了烧绿石族矿物中氧化还原敏感行为和铀同位素分馏的重要性，并加强了天然类似物在定制合成岩石成分方面的相关性。此类类似物作为经验基准，用于预测地质时间尺度上核废料储存库中含锕系元素相的性能。
