乙异羟肟酸与U、Np、Pu配合物的结构和热力学性质的密度泛函理论研究

采用密度泛函理论(DFT),在B3LYP/RECP/6-31G(d,p)水平对U(Ⅵ)、U(Ⅳ)、Np(Ⅳ)、Pu(Ⅳ)与乙异羟肟酸(AHA)摩尔比为1∶1和1∶2配合物的结构和热力学参数进行了研究。结构计算发现,M-O键键长随原子序数增加而减短,对配合物进行自然轨道分析(NBO)发现,M和AHA的摩尔比为1∶1的配合物中M-O键是明显的离子键,共价成分很少,在1∶2配合物中M-O键共价成分增加。对配位反应的热力学参数进行计算发现,金属离子与AHA配合物的稳定性依次为Pu(Ⅳ)Np(Ⅳ)U(Ⅳ)U(Ⅵ),理论计算结果与实验测量得到的稳定常数顺序一致。     

乙异羟肟酸改善Purex流程铀产品中U-Pu的分离

研究采用新的无盐络合剂乙异羟肟酸（ＡＨＡ）来改善Ｐｕｒｅｘ流程铀线Ｕ－Ｐｕ分离。萃取及洗涤体系中Ｐｕ（Ⅳ）及Ｕ（Ⅵ）的分配实验结果表明：ＡＨＡ能够很好地络合Ｐｕ（Ⅳ）,它既能抑制水相中Ｐｕ（Ⅳ）被３０％ＴＢＰ／ＯＫ萃取,又能有效地把萃取到３０％ＴＢＰ／ＯＫ中的Ｐｕ（Ⅳ）洗涤到水相。同时,ＡＨＡ的存在不影响３０％ＴＢＰ／ＯＫ对Ｕ（Ⅵ）的萃取。     

L边密度计稳定性监控及U、Pu测量

本文采用金属Zr片作为质控样品监控L边密度计的长期稳定性,在此基础上采用L边密度计测量系列水相U标准溶液和水相Pu标准溶液,绘制水相U工作曲线和水相Pu工作曲线,建立了L边密度计测量U、Pu的分析方法,并采用该工作曲线测量了系列U和Pu标准溶液。结果显示,该方法既可测量水相U、Pu,也可测量有机相U、Pu,对于10 g/L以上的U溶液,测量结果的相对偏差小于5%;对于5 g/L以上的Pu溶液,测量结果的相对偏差小于1.7%。以上结果表明,本文所建立的L边密度计测量U、Pu的方法准确度良好,可用于实际U、Pu的测量。     

Measurement of homogeneity of U and Pu isotopes in PWR spent fuel powder mixture

We present a feasibility study of the homogenization of pressurized water reactor spent nuclear fuel (SNF) powder through a mechanical mixing process. Because burn-up of the SNF depends on the position in the SNF assembly, concentrations of uranium, plutonium, and fission products are distributed differently according to the burn-up profile. The heterogeneity of the material elements affects the selection of a representative sample for quantitative analysis. Homogenization process improvement to reduce the sampling error is thus required to precisely determine the amount of uranium, plutonium, and fission products in the SNF. In this study, fine powders (<70 μm) extracted from one SNF rod were mixed, and the degree of homogenization was determined as a function of the mixing time indicating the relative standard deviations of the ¹³⁴Cs/¹³⁷Cs, Pu, and U isotope ratio measurements.     

Uncertainty Analyses in the Resolved Resonance Region of 235U, 238U,and 239Pu with the Reich-Moore R-Matrix Theory for JENDL-3.2

A simple method to estimate covariances for resolved resonance parameters was developed. Although a large number of resolved resonances are observed for major actinides, uncertainties in averaged cross sections are more important than those in resonance parameters in reactor calculations. The method developed here derives a covariance matrix for the resolved resonance parameters which gives an appropriate uncertainty of the averaged cross sections. The method was adopted to evaluate the covariance data for ²³⁵U, ²³⁸U, and ²³⁹Pu resonance parameters in JENDL-3.2, with the Reich-Moore R-matrix formula.     

Removal of Americium by Its Evaporation during Carbothermic Reduction of Plutonium Dioxide

The kinetic study of the reduction of U(VI) at the titanium electrode in nitric acid and hydrazine media was carried out at 25±0.5°C. Uranium (VI) is reduced through a totally irreversible process and kinetic parameters are affected by both the concentration of nitric acid and the electrolytic potential. An empirical equation to express the rate of the reduction of U(VI) was proposed and was confirmed to be in fairly good agreement with the amount of U(IV) produced by the controlled-potential electrolysis. The optimal condition for the preparation of U(IV) from U(VI) was found to be the electrolysis at -0.5V vs. Ag-AgC1/sat.KC1 in 1–2 M HNO₃ and 0.1–0.2_M hydrazine.     

DFT study on the bonding properties of Pu(III) and Pu(IV) chloro complexes

Understanding of chemical bonding is a fundamentally important topic. Given the importance of bonding studies, we performed quantum calculations on plutonium chloro complexes (PuClx(III) and PuClx(IV)) that are believed to form as molten chloride salts during nuclear waste treatment. The result of these calculations was verified by comparing them to experimental data on a similar actinide chloro complex. Charge and bond order analyses of the complexes provide insight into the electronic properties, bonding, and nuclear magnetic resonance characteristics of the plutonium chloro complexes. The chemical shift of the Pu(III) complexes are found to be negative while those of Pu(IV) are positive.     

离子色谱分离-峰面积比值法测定核燃料元件中的钚

建立了用离子色谱法和峰面积比值法分离U并测量核燃料元件中钚的方法。该方法可以消除铀等基体的干扰,色谱条件在一定范围内变化时对测量结果无影响。在一定色谱条件下,通过实验获得相同含量的钚铀峰面积之比后,实际测量时可不采用钚标准溶液对仪器进行校准。方法的检出限为0.05 mg/L。该方法适用于各种乏燃料元件中钚含量的测定。     

Thermodynamic behavior of (U,Pu) mixed-oxide fuels

Transpiration experiments were performed at temperatures between 1000 and 1700°C to study the thermodynamics and defect structure of hypostoichiometric UO₂-20 wt % PuO₂ solid-solution systems. The oxygen partial pressures were established by using flowing $\text{H}{}_2\text{/H}{}_2\text{O}$ mixtures. After equilibration, the quenched products were analyzed by chemical, X-ray, neutron-diffraction and metallographic techniques. The versus temperature curves for the mixed oxide with different oxygen-to-metal ratios were plotted.Based on X-ray, neutron diffraction and metallographic data, it was concluded that the 20 wt % PuO₂ mixed oxide exists as a single phase under normal conditions, even at an oxygen-to-metal ratio as low as 1.92.The data from density measurements and neutron-diffraction analysis indicated that the predominant defects in the hypostoichiometric UO₂-20 wt % PuO₂ are anion vacancies.     

西北太平洋表层海水中239+240Pu浓度及240Pu/239Pu同位素比

钚是与核工业密切相关的敏感元素,是来源于人类核活动、以痕量或超痕量水平存在于环境中的重要锕系元素。与陆地土壤中钚的环境行为不同,输入到海洋环境中的钚会随洋流路径进行远距离迁移扩散。因此,对于包括我国近海在内的西北太平洋区域海水,除受全球沉降影响外,还长期受到美国太平洋核试验场（PPG）所造成区域污染的显著影响。本文利用从相关报道中收集的数据,对西北太平洋表层海水中钚浓度及同位素比的分布特征进行了分析。结果表明,2000年至今,西北太平洋表层海水中^239+240Pu浓度和²⁴⁰Pu/²³⁹Pu同位素比分别在1.15~22.3 mBq/m³和0.184~0.31间变化,其中,^239+240Pu浓度分布与西北太平洋各区域的环境条件等密切相关,而²⁴⁰Pu/²³⁹Pu分布则相对均匀,后者在除中国南海以外的西北太平洋地区均值为0.247±0.025(1σ),据此估算得美国太平洋核试验场区域污染输入的钚对该海域表层海水中钚的贡献约占其总活度的45%。此外,本文还对福岛核电站附近海域中核事故前后钚的相关数据进行了分析对比,未观察到该事故对西北太平洋海域中钚分布的影响。     

Measurement of Average Cross Section for 238U(n, 2n)237U Reaction

Accurate solution of the group diffusion equations for PWR cores requires explicit treatment of the non-homogeneous macroscopic parameters within each fuel assembly. It is argued that the response matrix approach is a convenient method to handle this problem provided all matrix elements for the non-homogeneous assemblies can be computed. This so called local problem is solved in this paper by a perturbation algorithm which leads to sensitivity coefficients for the power series expansions of the response matrix elements. A numerical study for 2 representative assemblies of the Indian Point Unit No. 2 (IP2) reactor is carried out and response matrices obtained by the perturbative method are compared with values computed by a finite difference program.     

Thermal conductivity of near-stoichiometric (U, Ce)C and (U, Pu, Ce)C solid solutions

The thermal conductivities of near-stoichiometric (U, Ce)C and (U, Pu, Ce)C solid solutions containing CeC up to 10 mol% were determined in the temperature range from 740 to 1600 K by the laser flash method. The thermal conductivity decreased with the cerium content in the solid solutions. The electrical resistivities were also measured for the purpose of analyzing the heat conduction mechanism. It was found that the decrease of electronic heat conduction caused by the addition of cerium resulted in decreasing the thermal conductivities of (U, Ce)C and (U, Pu, Ce)C compared with UC and (U, Pu)C.     

Pu在花岗岩中的吸附行为

为了解Pu在甘肃北山地区地下深度约为600 m的花岗岩中的吸附行为,研究了各种水质(重蒸水、模拟地下水、BS03井地下水)、pH值(3.0~10.0)、CO32-离子浓度(4.0×10-3~1.0×10-1mol/L)、氧浓度等因素对吸附的影响。通过对吸附后水相物化参数(如pH值、Eh、电导率等)、Pu的价态、固相表面特征参数(比表面、孔径、总孔容等)等数据的比较以及解吸实验结果,推测可能的吸附机理:Pu在花岗岩上以表面配合物的形式吸附,且可用Freundlich吸附等温式描述。     

Behavior and Removal of Impurity Sulphate in Sol-Gel Process for ThO2 and (Th,U)O2 Microsphere Fabrication

The behavior of impurity sulphate, fed from source Th(NO₃)₄, in a sol-gel process for fabricating (Th, U)O₂ microspheres is studied. In sols, almost all the sulphates are adsorbed on colloid particles regardless of U content U/M (M:Th+U). However, the sulphate in gelmicrospheres is easily washed out for U/M higher than 10mol/₀, while not for lower U/M; especially, the sulphate in ThO₂ gel-microspheres is difficult to be removed even by long-time washing. The sulphur remaining in the gel-microspheres is able to be removed out by heating in air or steam at 1,000°C for 3h; as for ThO₂, slight residue is found but not after 1,300°C heating. On the other hand, heating them in Ar-4%H₂ atmosphere, even at 1,500°C, allows most of the sulphur to remain as an unidentified M-O-S compound; during the heating, the sulphur is gradually released by the reaction with H₂ to form H₂S.

The study finds optimum conditions for removal of the impurity sulphate in the sol-gel process.     

铀属性测量中的时间关联符合法研究进展

综述了在铀属性测量中,时间关联符合法的研究进展情况,简要地介绍了铀、钚的属性,核材料的被动与主动探测方式、时间关联符合法的基本原理、起源和发展,详细地归纳了时间关联符合法在计算方法、数值模拟、实验研究和应用研究四个方面的国内外研究现状,并分析了发展趋势及需要解决的问题。