Feasibility of the electrochemical way in molten fluorides for separating thorium and lanthanides and extracting lanthanides from the solvent

An alternative way of reprocessing nuclear fuel by hydrometallurgy could be using treatment with molten salts, particularly fluoride melts. Moreover, one of the six concepts chosen for GEN IV nuclear reactors (Technology Roadmap - http://gif.inel.gov/roadmap/) is the molten salt reactor (MSR). The originality of the concept is the use of molten salts as liquid fuel and coolant. During the running of the reactor, fission products, particularly lanthanides, accumulate in the melt and have to be eliminated to optimise reactor operation. This study concerns the feasibility of the separation actinides-lanthanides-solvent by selectively electrodepositing the elements to be separated on an inert (Mo, Ta) or a reactive (Ni) cathodic substrate in molten fluoride media. The main results of this work lead to the conclusions that:

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The solvents to be used for efficient separation must be fluoride media containing lithium as cation.

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Inert substrates are suitable for actinide/lanthanide separation; nickel substrate is more suitable for the extraction of lanthanides from the solvent, owing to the depolarisation occurring in the cathodic process through alloy formation.

     

Refinement in the ultrasonic velocity data and estimation of the critical parameters for molten uranium dioxide

Based on the previously reported internal pressure approach and by making use of recent and more accurate experimental measurements on the density, and heat capacity of liquid UO₂ up to ∼8000 K, reliable data on the sound propagation velocity in molten uranium dioxide have been obtained. An equation of state for liquid urania has also been developed which predicts a critical temperature (T_c) ≈ 10 500 K, critical pressure (P_c) ≈ 219 MPa and critical density (ρ_c) ≈ 2510 kg m⁻³.     

Examination of U valence states in the brannerite structure by near-infrared diffuse reflectance and X-ray photoelectron spectroscopies

The valence state of uranium doped into a f⁰ thorium analog of brannerite (i.e., thorutite) has been examined using near-infrared (NIR) diffuse reflectance (DRS) and X-ray photoelectron (XPS) spectroscopies. NIR transitions of U⁴⁺, which are not observed in spectra of brannerite, have been detected in the samples of U_xTh_1−xTi₂O₆, and we propose that strong specular reflectance is responsible for the lack of U⁴⁺ features in UTi₂O₆. Characteristic U⁵⁺ bands have been identified in samples in which sufficient Ca²⁺ has been added to nominally effect complete oxidation to U⁵⁺. XPS results support the assignments of U⁴⁺ and U⁵⁺ by DRS. The presence of residual U⁴⁺ bands in the spectra of the Ca-doped samples is consistent with segregation of Ca²⁺ to the grain boundaries during high temperature sintering.     

Damage inhomogeneity in the core region of displacement cascades in simplified nuclear glasses

Displacement cascades at energies ranging from 16 keV to 70 keV were simulated by classical molecular dynamics. Damage inhomogeneity was observed in each case: the atomic density was diminished by the incident projectile to a variable extent depending on the regions concerned. The regions near the initial projectile position are largely annealed, and regions near the end of the cascade are relatively unaffected because of the low residual projectile energy. However, maximum damage occurs in intermediate regions from collisions with incident projectiles at energies ranging from about 10 keV to 25 keV. This phenomenon illustrates the competition between structure annealing and projectile-induced damage: both increase with the local energy, but with different dynamics. At the highest energies, annealing wins out over damage, restoring the glass structure to its pristine state; hence the good structural behaviour in the zones closest to the initial projectile position, which are subjected to the greatest local temperature rise.     

The development of a stress analysis code for nuclear graphite components in gas-cooled reactors

Most of the UK nuclear power reactors are gas-cooled and graphite moderated. As well as acting as a moderator the graphite also acts as a structural component providing channels for the coolant gas and control rods. For this reason the structural integrity assessments of nuclear graphite components is an essential element of reactor design. In order to perform graphite component stress analysis, the definition of the constitutive equation relating stress and strain for irradiated graphite is required. Apart from the usual elastic and thermal strains, irradiated graphite components are subject to additional strains due to fast neutron irradiation and radiolytic oxidation. In this paper a material model for nuclear graphite is presented along with an example of a stress analysis of a nuclear graphite moderator brick subject to both fast neutron irradiation and radiolytic oxidation.     

核设施退役辐射检测及其仪器仪表应用

核设施退役辐射场检测技术在核设施退役的整个过程中起着非常重要的作用.较系统论述了核设施退役辐射检测的质量保证,最后从满足核设施退役工作的需要出发,评述了退役过程辐射检测仪器仪表的选择及其应用.指出国内辐射监测仪器仪表在满足核设施退役的需求上的较大差距,值得各有关方面关注.     

中国核动力院核基地外围空气CO 2中14C分布特征及所致公众年有效剂量评价

基于2014—2017年中国核动力院核基地外围环境空气中¹⁴C的监督性监测数据,对关键居民组各种途径的待积有效剂量进行了粗略的估算。结果表明:综合楼与南坝工会空气中¹⁴C活度浓度差异有统计学意义,综合楼与木城水厂空气中¹⁴C活度浓度差异有统计学意义,南坝工会与木城空气中¹⁴C活度浓度差异无统计学意义,表明排放出来的¹⁴CO₂在空气中扩散混合很快。综合楼附近居民组中成人、青少年、儿童、幼儿经各途径的¹⁴C年平均摄入量分别为40.55、40.52、29.10、19.80 kBq/a;年待积有效剂量分别为23.31、22.91、23.08、19.44 μSv/a。其中成人组成员所受¹⁴C致待积有效剂量最大为23.31 μSv/a,但此待积有效剂量也仅占评价剂量目标值(0.25 mSv)的9.3%以下。由此可以得出,核基地核施设正常运行工况下,¹⁴C对核基地外围环境的影响很小。     

The role of the reactor size for an investment in the nuclear sector: An evaluation of not-financial parameters

The literature presents many studies about the economics of new Nuclear Power Plants (NPPs). Such studies are based on Discounted Cash Flow (DCF) methods encompassing the accounts related to Construction, Operation & Maintenance, Fuel and Decommissioning. However the investment evaluation of a nuclear reactor should also include not-financial factors such as siting and grid constraints, impact on the national industrial system, etc.The Integrated model for the Competitiveness Assessment of SMRs (INCAS), developed by Politecnico di Milano cooperating with the IAEA, is designed to analyze the choice of the better Nuclear Power Plant size as a multidimensional problem. In particular the INCAS’s module “External Factors” evaluates the impact of the factors that are not considered in the traditional DCF methods.This paper presents a list of these factors, providing, for each one, the rationale and the quantification procedure; then each factor is quantified for the Italian case. The IRIS reactor has been chosen as SMR representative.The approach and the framework of the model can be applied to worldwide countries while the specific results apply to most of the European countries. The results show that SMRs have better performances than LRs with respect to the external factors, in general and in the Italian scenario in particular.     

A detailed study of the d + B system for nuclear reaction analysis - Part A: The B(d,p)B reaction in the energy region Ed,lab = 900-2000 keV

The differential cross-sections of the ¹⁰B(d,p_{0,1,2,3,4-5,6}) reactions for the determination of the depth distribution of boron in near-surface layers of materials have been determined in the projectile energy region E_d,lab = 900-2000 keV. The experiment was carried out in energy steps of 25 keV and for eight detector angles between 135° and 170° (in steps of 5°). The obtained experimental data are suitable for nuclear reaction analysis (NRA) studies. A qualitative discussion of the observed cross-section variations through the strong influence of overlapping resonances in the d + ¹⁰B system is also presented.