Research Centre for Radwaste Disposal & Williamson Research Centre for Molecular Environmental Science, Department of Earth and Environmental Sciences, University of Manchester, Oxford Road, Manchester M13 9PL, U.K.
Civil and Environmental Engineering, University of Strathclyde, Glasgow, G11XQ, U.K.
Environ Sci Technol. 2021 Apr 20;55(8):4597-4606. doi: 10.1021/acs.est.0c03594. Epub 2021 Mar 23.
Geological disposal is the globally preferred long-term solution for higher activity radioactive wastes (HAW) including intermediate level waste (ILW). In a cementitious disposal system, cellulosic waste items present in ILW may undergo alkaline hydrolysis, producing significant quantities of isosaccharinic acid (ISA), a chelating agent for radionuclides. Although microbial degradation of ISA has been demonstrated, its impact upon the fate of radionuclides in a geological disposal facility (GDF) is a topic of ongoing research. This study investigates the fate of U(VI) in pH-neutral, anoxic, microbial enrichment cultures, approaching conditions similar to the far field of a GDF, containing ISA as the sole carbon source, and elevated phosphate concentrations, incubated both (i) under fermentation and (ii) Fe(III)-reducing conditions. In the ISA-fermentation experiment, U(VI) was precipitated as insoluble U(VI)-phosphates, whereas under Fe(III)-reducing conditions, the majority of the uranium was precipitated as reduced U(IV)-phosphates, presumably formed via enzymatic reduction mediated by metal-reducing bacteria, including Geobacter species. Overall, this suggests the establishment of a microbially mediated "bio-barrier" extending into the far field geosphere surrounding a GDF is possible and this biobarrier has the potential to evolve in response to GDF evolution and can have a controlling impact on the fate of radionuclides.
地质处置是全球首选的高活度放射性废物（HAW）长期解决方案，包括中活度废物（ILW）。在水泥固化处置系统中，ILW 中存在的纤维素废物可能会发生碱性水解，产生大量的异抗坏血酸（ISA），这是一种放射性核素的螯合剂。尽管已经证明了 ISA 的微生物降解，但它对地质处置设施（GDF）中放射性核素命运的影响是一个正在研究的课题。本研究调查了在 pH 值中性、缺氧、微生物富集培养物中 U(VI)的命运，这些培养物接近 GDF 远场的条件，其中 ISA 是唯一的碳源，且含有高浓度的磷酸盐，分别在（i）发酵和（ii）Fe(III)还原条件下进行培养。在 ISA 发酵实验中，U(VI)被沉淀为不溶性 U(VI)-磷酸盐，而在 Fe(III)还原条件下，大部分铀被沉淀为还原的 U(IV)-磷酸盐，据推测这是通过包括 Geobacter 属在内的金属还原细菌介导的酶还原形成的。总体而言，这表明在 GDF 周围的远场地球层中建立微生物介导的“生物屏障”是可能的，并且这种生物屏障有可能根据 GDF 的演化而演化，并对放射性核素的命运产生控制作用。
