A study on the burn-up characteristics of inert matrix fuels

Proper disposal of minor actinides (MA), long-lived fission products (LLFPs), and transuranium element (TRU) plays a key role in the sustainable development of fission nuclear power. Adoption of inert matrix fuels (IMFs) can effectively reduce the amount of ²³⁷Np and Np element in the spent fuel of present-day commercial power reactors. In order to study the burn-up characteristics of IMFs caused by the unique composition, burn-up calculations and MA accumulation of two typical IMFs, PuO₂ + ZrO₂ + MgO and PuO₂ + ThO₂, are performed in this paper. Results indicate that k_inf at beginning of life (BOL) and reactivity drop with burn-up for PuO₂ + ZrO₂ + MgO are much larger than those of PuO₂ + ThO₂ IMF. The yields of ²³⁷Np and Np element in IMFs are two orders smaller than those of UO₂ and mixed oxide (MOX) fuels. For the same PuO₂ volume fraction and a certain burn-up, the masses of ²³⁷Np, Np element, and ²⁴¹Am for PuO₂ + ZrO₂ + MgO are smaller than those of PuO₂ + ThO₂; however, the mass of total MA is larger. IMF has high destruction efficiencies of TRU and plutonium (Pu). The results and conclusion provide basic data for the ongoing IMF design and application study.     

A study on selective precipitation of U(VI) by hydrophilic cyclic urea derivatives for development of a reprocessing system based on precipitation method

Selective precipitation ability of 2-imidazolidone (EU) and tetrahydro-2-pyrimidinone (PU) for U(VI) species in HNO₃ solutions containing U(VI), U(IV) (simulant of Pu(IV)), and simulated fission products (FPs) was investigated. As a result, it was found that these compounds precipitate almost quantitatively U(VI) as UO₂(NO₃)₂L₂ (L = EU, PU) from 3.0 M HNO₃ solution. In contrast, these urea derivatives form neither solid precipitates nor oily products with U(IV) in HNO₃ solutions containing only U(IV) species and even in U(VI)–U(IV) admixture system. Therefore, the separation of U(VI) from U(IV) was demonstrated to be achieved in use of EU and PU. Furthermore, EU and PU are capable to remove most of simulated FPs[Sr(II), Ru(III), Rh(III), Re(VII) La(III), Ce(III), Pr(III), Nd(III), and Sm(III)] from U(VI) to give their decontamination factors (DFs) higher than 100, while those values of Zr(IV), Mo(VI), Pd(II), and Ba(II) are necessary to be improved in both systems. From these results, it is expected that EU and PU are the promising precipitants for selective separation of U(VI) from HNO₃ solutions dissolving spent FBR fuels.     

钧瓷铜红釉呈色机制的初步研究

利用同步辐射光源,对一枚带红釉的元代钧瓷表面进行了无损的X射线吸收精细结构分析(SR-XAFS).将釉中铜的相关标准谱作线性拟合,并与样品的近边图谱作比较分析,结果表明,红釉层内,铜的存在状况为:37%的单价铜和63%的零价铜,零价铜主要以金属团簇或多聚体形式存在其中.而在红釉表面,则主要为单价铜.对延展边的处理结果表明,单价铜孤立地镶嵌在玻璃体网格结构中.铜的这些特殊存在形式导致了钧釉独特的光学性质.另外,采用同步辐射X射线荧光光谱(SRXFS)分析技术,无损测定了釉中元素的分布特征,最后,尝试对这些复杂结构的形成机理进行了探讨.     

Scenario with inert matrix fuel: a specific study

In this paper, we describe a strategy study concerning the future of the French nuclear energy infrastructure, with a scenario involving reactors loaded with inert matrix fuel. We select the problem of the inventory control of minor actinides by target introduction into fast reactors. Added to pressurized water reactors in the French nuclear infrastructure, this scenario permits one to balance plutonium and minor actinide production and consumption and to obtain a substantial reduction of the radiological impact compared to a non-reprocessing fuel scenario on a one million year scale.     

A study on selective precipitation ability of cyclic urea to U(VI) for developing reprocessing system based on precipitation method

We have proposed a new reprocessing system based on precipitation method. In order to find out precipitants with high selectivity to U(VI) and to investigate factors controlling precipitation ability to U(VI) and U(IV), properties of 3,4,5,6-tetrahydro-1,3-dimethyl-2(1H)-pyrimidinone (DMPU) as a precipitant have been examined by using U(VI), U(IV) as a simulant of Pu(IV), and simulated fission products (FPs). We have evaluated precipitation ratios (P.R.) for U(VI) and U(IV), solubility of U(VI) precipitates to 3.0 mol dm^?3 (M) HNO₃ solution, melting points (MPs) of U(VI) precipitates, log P (distribution ratio of a substance in 1-octanol/water biphasic system, a measure of hydrophobicity) of precipitants, and decontamination factors (DFs) of FPs. The properties of DMPU were compared with those in systems using N-n-butyl-2-pyrrolidone (NBP), N-cyclohexyl-2-pyrrolidone (NCP), and other pyrrolidone derivatives as the precipitant. The P.R. values of DMPU to U(VI) and U(IV) in 3.0 M HNO₃ solutions were around 99% at [DMPU]/[U(VI)] = 2.0 and 0% at [DMPU]/[U(IV)] = 5.0, respectively. In DMPU system, the DF values of the most of simulated FPs [Rb(I), Cs(I), Sr(II), Ba(II), Ru(III), Rh(III), La(III), Ce(III), Pr(III), Nd(III), and Sm(III)] used in the present study were found to be more than 100. Even in U(VI)–U(IV) coexisting system, the selectivity of DMPU to U(VI) was higher than those of NBP and NCP. This selective precipitation ability of DMPU to U(VI) was evaluated by the solubility of U(VI) precipitates on the basis of their MPs and the log P values of precipitants. As a result, it was found that the precipitants having low hydrophobicity and forming the U(VI) precipitates with high MPs have highly selective precipitation ability to U(VI).     

无损测定铀材料上铝镀层厚度的研究

为探讨初级X射线与铝镀层和铀工体物质、铀的特征线与铝镀层之间的相互作用以及铀基体的放射性对测量铝厚度的影响程度,提出强度与镀层厚度关系的数学模型,以及在同一数学模型中,根据铝镀层厚度的实际情况分别选用铀的M和L线测定薄样和厚样。建立了无损测定铀材料上铝镀层厚度（8．2－55．5μm）的测试方法。对8．2－18μm的薄试样,方法的精密度优于3％;对18－－55．5μm的厚试样,方法的精度密度优于5％。     

A study of grain boundary sliding in copper with and without an addition of phosphorus

Copper will be used as a corrosion barrier in the storage of high level nuclear waste. In order to improve the creep fracture properties of the material it will contain 30-50 ppm of phosphorus, OFP copper as opposed to OF copper without P. It has been suggested that the phosphorus impedes grain boundary sliding in copper and recently a quantitative theory based on this idea has shown that there is no risk for creep-brittle fracture of OFP copper under waste storage conditions. In order to verify the basis of this theory grain boundary sliding has been investigated in copper with and without a P addition. The method has been to examine intentionally scratched surfaces of tensile specimens tension tested to plastic strains of 1%, 2% and 4% at 150 and 200 °C. After testing specimen surfaces have been examined in SEM and sliding distances have been measured as in-surface displacement of scratches. The results have been plotted as distribution functions where the fraction of slides smaller than a given value is plotted versus sliding distance. The result is that in most cases the distribution functions for OF and OFP copper overlap. In a small number of cases there is a tendency that less sliding has occurred in OFP copper. The overall conclusion is however that although there may be a slight difference between the materials with regard to grain boundary sliding it is not large enough to explain the observed difference in creep brittleness. Tension tests to fracture in the temperature range 100-200 °C show that the tensile properties of the two copper qualities are more or less identical until intergranular cracking starts in the OF copper. Then the flow stress decreases in comparison with OFP. It is suggested that at least part of the observed differences in creep strength between the two coppers may be due to the effect of intergranular cracking.     

Synchrotron diffraction study of dissolution and precipitation kinetics of hydrides in Zircaloy-4

This paper presents observations of in situ heating and cooling cycles using synchrotron X-ray diffraction carried out on Zircaloy-4 plates charged to different levels of hydrogen content. The diffraction peak intensities were used to derive the weight fraction of hydrogen in solid solution and the solvi curves upon dissolution and precipitation. The heating and cooling rate did not seem to have a major influence on the solvi. Fast-cooling/dwell experiments showed that the precipitation kinetics are very fast. Finally the evolutions of the lattice strains from individual grain families were studied during dissolution and precipitation. The aim was to understand the role of interphase misfit stresses on the mechanisms of hydride formation and hysteresis between dissolution and precipitation. The results emphasise that changes in dissolved H concentration are responsible for a non-negligible part of the lattice distortion in the matrix, and that the diffraction strains must therefore be analysed with care.     

A critique of the stochastic transition matrix formalism

The Stochastic Transition Matrix (STM) formalism has been introduced by Akcasu to compute the ensemble average flux of bimaterial stochastic density statistics with deterministic sources. The method uses an integral flux representation based on a stochastic propagator and as boundary conditions the entering and exiting fluxes at the left of a finite slab. In this paper we generalize the STM formalism to the energy-dependent continuous transport equation, analyze and discuss basic issues of the formalism and compare it to the classical Levermore–Pomranig model and to reference calculations for simplified rod problems. We also extend the formalism in two different ways to consistently compute the ensemble and the material averages flux.     

Energy-loss distributions for single particles and several particles in a thin silicon absorber

The energy-loss distributions for protons, with kinetic energies between 220 and 850 MeV, and for several relativistic particles produced at incoming beam momentum of 115 GeV/c, have been measured in an ion-implanted silicon detector of 300 μm thickness. The data are well descrìbed by an improved energy-loss distribution which takes into account the long-distance collisions disregarded in both the Landau and Vavilov distributions.     

Design feasibility study of a divertor component reinforced with fibrous metal matrix composite laminate

Fibrous metal matrix composites possess advanced mechanical properties compared to conventional alloys. It is expected that the application of these composites to a divertor component will enhance the structural reliability. A possible design concept would be a system consisting of tungsten armour, copper composite interlayer and copper heat sink where the composite interlayer is locally inserted into the highly stressed domain near the bond interface. For assessment of the design feasibility of the composite divertor concept, a non-linear multi-scale finite element analysis was performed. To this end, a micro-mechanics algorithm was implemented into a finite element code. A reactor-relevant heat flux load was assumed. Focus was placed on the evolution of stress state, plastic deformation and ductile damage on both macro- and microscopic scales. The structural response of the component and the micro-scale stress evolution of the composite laminate were investigated.     

Release of short-lived noble gases from HTGR fuel with failed coated fuel particles and contaminated matrix

Fuel compacts of the high-temperature gas-cooled reactor may contain a fraction of exposed uranium as defective coated fuel particles and a contamination of graphite matrix. Releases of short-lived noble gases were measured on the fuel compacts containing artificial failed particles as well as those having a highly contaminated matrix. The results were compared with the prediction by the JAERI model of short-lived gas release, which has been generated from previous irradiation testings. The release from the compacts with artificial failed particles agreed with the prediction except at lower temperatures where the fission-induced diffusion would predominate. The release from the matrix-contaminated compacts was different from the model prediction: The model fairly accurately predicted R/B of Xe, but significantly overpredicted that of Kr.