锆英石基An4+放射性核素固化体性能研究

为研究锆英石基An4+(四价锕系核素)放射性核素固化体的性能,利用Ce4+作为An4+的模拟替代物质,以ZrO2、SiO2和CeO2粉体为原料,采用高温固相法制备出包容20%(物质的量,下同)Ce4+的锆英石基固化体,利用60Co源γ射线辐照装置对其进行572.1kGy的γ射线辐照.利用粉末X射线衍射仪、扫描电子显微镜和电感耦合等离子体质谱仪对γ射线辐照前后固化体的物相、结构、微观形貌及模拟核素的浸出行为进行了研究.结果表明,固化体中虽包容有20%的Ce4+,但其主物相仍以锆英石物相为主,与标准样品相比晶胞参数发生10-4nm量级的变化,经γ射线辐照后样品晶胞参数仅发生了10-5~10-4nm量级的微弱变化,在pH6.5的HCI浸出液中Ce4+的平衡浓度低于0.30μg/L.     

Review of the complexation of tetravalent actinides by ISA and gluconate under alkaline to hyperalkaline conditions

Isosaccharinic (ISA) and gluconic acids (GLU) are polyhydroxy carboxylic compounds showing a high affinity to metal complexation. Both organic ligands are expected in the cementitious environments usually considered for the disposal of low- and intermediate-level radioactive wastes. The hyperalkaline conditions imposed by cementitious materials contribute to the formation of ISA through cellulose degradation, whereas GLU is commonly used as a concrete additive. Despite the high stability attributed to ISA/GLU complexes of tetravalent actinides, the number and reliability of available experimental studies is still limited. This work aims at providing a general and comprehensive overview of the state of the art regarding Th, U(IV), Np(IV), and Pu(IV) complexes with ISA and GLU.In the presence of ISA/GLU concentrations in the range 10^− 5–10^− 2 M and absence of calcium, An(IV)(OH)_x(L)_y complexes (An(IV) = Th, U(IV), Np(IV), Pu(IV); L = ISA, GLU) are expected to dominate the aqueous speciation of tetravalent actinides in the alkaline pH range. There is a moderate agreement among their stability, although the stoichiometry of certain An(IV)-GLU complexes is still ill-defined. Under hyperalkaline conditions and presence of calcium, the species CaTh(OH)₄(L)₂(aq) has been described for both ISA and GLU, and similar complexes may be expected to form with other tetravalent actinides.In the present work, the available thermodynamic data for An(IV)–ISA/GLU complexes have been reviewed and re-calculated to ensure the internal consistency of the stability constants assessed. Further modelling exercises, estimations based on Linear Free-Energy Relationships (LFER) among tetravalent actinides, as well as direct analogies between ISA and GLU complexes have also been performed. This approach has led to the definition of a speciation scheme for the complexes of Th, U(IV), Np(IV) and Pu(IV) with ISA and GLU forming in alkaline to hyperalkaline pH conditions, both in the absence and presence of calcium.     

QUANTIFICATION OF ACTINIDE MIGRATION PATHWAYS AT ROCKY FLATS,COLORADO1

ABSTRACT: Migration of plutonium, americium, and uranium (actinides) in the environment at the Rocky Flats Environmental Technology Site (RFETS) is the subject of ongoing studies to develop effective strategies for cleanup and regulatory closure of the Department of Energy facility. The Actinide Migration Evaluation pathway analysis quantified actinide transport processes to validate a qualitative conceptual model of environmental actinide transport. Major actinide transport mechanisms evaluated include surface water, ground water, airborne, and biological pathways. Relative quantities of actinide movement via different pathways were compared in terms of actinide loads delivered off the RFETS, using a combination of monitoring data, predictive transport models and results from historic RFETS studies. Results indicate air and surface water constitute the dominant transport mechanisms for plutonium and americium. In ground water, shallow alluvial flow is a limited pathway for plutonium and americium because of the low aqueous solubility of these actinides and their tendency to sorb to soil. However, localized flow in shallow alluvium is a more significant pathway for uranium movement, because of the relatively higher solubility of uranium (VI) species, though isotopic ratios indicate much of the uranium is from natural sources. Biological transport of actinides by mammals, birds, fish, and arthropods is small compared to the other pathways.