U-10Mo/Al-2Si扩散层性质研究

采用热压扩散偶方法研究了U-10Mo/Al-2Si的扩散层性质.实验在真空热压炉中完成,温度550～570℃.时间5～21 h.结果表明:扩散层随时间的延长和温度的提高而增厚;U-Mo侧生成了抑制U-Mo/Al的扩散反应,Si含量高达47.4%(原子分数)的富Si层.从U-Mo侧到Al-2Si侧,U和Mo的含量递减而A...     

U-Mo合金与Al扩散反应特征研究

采用扩散偶方法研究了U-Mo合金与Al扩散反应特征.扩散偶以热压方式实现持续贴合.实验在真空热压炉中完成,热压温度550-570℃,时间5～21 h.结果表明:U-Mo/Al扩散层界面形貌和成分与扩散层厚度有关;在扩散层界面处U、Mo和Al的含量突变;U-Mo侧扩散层产物主要为(U,Mo)Al3,Al侧产物为(U,Mo)Al4和UMo2Al20.U-Mo/Al扩散反应是Al越过U-Mo/Al原始界面向U-Mo侧扩散并发生固体反应和扩散层向Al层生长的过程.     

U-Mo合金γ相稳定性研究

研究了U-Mo、U-Mo-X（X＝Ti、V、Si）合金及U-Mo/Al、U-Mo-X/Al扩散偶界面层的γ相稳定性,探讨了合金元素和退火工艺对γ相稳定性的影响。结果表明：Mo含量越高,U-Mo合金的γ相稳定性就越高;U-6.5Mo-0.5Si合金的γ相稳定性较高,是因为U Si混合焓较低,但加入Si易导致形成USi_x脆性相;而U-6.5Mo-0.5Ti和U-6.5Mo-0.5V合金的γ相稳定性较差,是因为Mo在Ti、V体系内具有较低的混合焓,易形成固溶体或金属间化合物,导致γ相贫Mo;随着退火温度从500℃升高至600℃,γ相发生共析分解,扩散层的γ相数量减少,α相增多,α相成为Al的快速扩散通道,促使形成UAl₄、UMo₂Al₂₀和U₆Mo₄Al₄₃等富Al相。     

U-Mo-Zr／Al-Si的互扩散行为

通过弥散体和扩散偶堆外退火试验，研究了Zr添加到U-Mo合金对U-Mo-Zr和Al-si反应的影响。Zr含量为1wt．％、2wt．％和4wt．％的U-7wt．％Mo合金锭由真空感应熔炼而成，采用离心雾化法制成粉末。对经γ相热处理过的U-7Mo-Zr合金进行高温退火试验，研究其γ相稳定性。X射线衍射分析结果表明：U-7Mo-Zr合金的γ相分解与U-7Mo合金类似。为研究互扩散行为，使用U-Mo-Zr粉末和Al-（0、0．4、2、5）wt．％Si合金粉末制备了弥散型样品。采用和弥散型样品化学成份相同的材料制备了扩散偶样品并进行了退火试验，以比较弥散型样品和扩散偶样品的互扩散行为。高Zr含量的弥散型样品在600℃时互扩散速度小幅增大，而扩散偶样品表明Zr添加到U-7Mo中降低了反应增长速度。Si能够减缓反应增长速度。U-Mo合金中添加的Zr没有在反应层中富集，而添加到～中的Si在反应层富集。U-Mo-Zr／Al-Si扩散偶中形成的反应产物为富Si的U（Si、Al）2。     

U-10wt%Mo合金与LT24Al的反应层性质研究

对U-10wt%Mo合金和LT24Al合金的反应层性质做了较详细的研究.将U-Mo/Al扩散偶试样在不同条件下进行热压处理,用光学显微镜(OM)和扫描电子显微镜(SEM)分析反应层的厚度,用能谱仪(EDS)分析各元素在反应区内的分布情况,用X射线衍射仪(XRD)测定了反应层的相组成.分析结果表明:U-Mo合金与Al的扩散方式是反应扩散,方向主要为Al原子通过空位扩散向U-Mo合金中迁移;反应层生长动力学表明反应为扩散所控制;U-Mo/Al的单相反应层主要由(U, Mo)Al3组成;两相或多相反应层主要由(U, Mo)Al3和(U, Mo)Al4组成,此外还含有Al20Mo2U;Al中的杂质Si容易在反应层中富集,这种趋势说明Si对改善U-Mo合金和Al的相容性起积极作用.     

弥散燃料板芯体中U-Mo/Al-Si合金基体反应层性质研究

针对弥散型燃料板采用实验方法分析U-Mo燃料相与Al-Si基体反应层的性质。实验结果表明:反应层主要出现在U-Mo燃料颗粒的内部微裂纹处及燃料颗粒与基体界面处,其形貌和厚度均不规则。U-Mo与Al-Si遵循空位扩散机制,扩散过程主要为Al、Si向U-Mo合金的扩散。在反应层中Al含量基本维持不变,Si含量沿基体-燃料相方向递增,并聚集在U-Mo侧的反应层中。当基体中Si含量达到5%时,可明显抑制扩散反应的进行,从而改进燃料板性能。     

不同温度下Al-Si共晶合金与Zr-2合金的相容性研究

用粉末冶金工艺制备了Al-Si共晶合金与Zr-2合金扩散偶,研究了不同等温热处理温度和时间条件下扩散偶的相容性.采用扫描电镜(SEM)、能谱分析(EDS)和X射线衍射(XRD)技术分析了扩散偶界面处的微观形貌和元素分布,讨论了扩散层形成机理.结果表明,环境温度及材料状态显著影响扩散偶之间的相容性.650℃时,液态Al-Si合金对Zr-2合金的浸润和扩散形成了较明显的以Zr3Al化合物为主的扩散层;560℃时,扩散元素之间仅产生固态扩散,形成的扩散层很薄;350℃时,扩散系数更小,几乎未发生扩散和形成扩散层,Al-Si共晶合金与Zr-2合金之间具有良好的相容性.     

Al-Si共晶合金与1Cr18Ni9Ti不锈钢的相容性研究

用粉末冶金法制备了Al-Si共晶合金与1Cr18Ni9Ti不锈钢反应堆扩散偶。采用电子显微镜（SEM）、能谱分析仪（EDS）、X射线衍射仪（XRD）D究了扩散偶在560℃和650℃时的相容性及扩散层形成机理。结果表明，扩散温度对两种材料之间的相容性有显著影响；650℃时，Al-Si共晶合金与1Cr18Ni9Ti之间通过浸润和扩散反应形成了比较明显的扩散层。XRD谱也表明，扩散层中存在Fe2Al5化合物；560℃时Al-Si共晶合金与1Cr18Ni9Ti之间仅发生固相反应，形成的扩散层很薄，二者相容性较好。     

U-Mo合金与Zr合金的相容性研究

采用扩散偶方法研究U-Mo合金与Zr的相容性。扩散偶采用包覆热轧法制备,热处理温度为750℃和800℃,热处理时间为10 h和50 h。结果表明:U-Mo合金与Zr合金间的扩散层有分层现象,在U-Mo/Zr界面扩散反应成分复杂界面处存在类似Mo2Zr的析出物。经X射线衍射(XRD)检测表明U-Mo/Zr扩散层由M2Zr、UZr2和U等组成。U-Mo/Zr的扩散过程是U和Mo原子向Zr扩散,Mo优先与Zr反应生成Mo2Zr、U通过Mo2Zr扩散形成γ-(U,Zr)固溶体的过程。U-Mo合金与Zr具有良好的相容性。     

U-Mo合金与Zr-4合金的扩散层性质研究

本文对U-Mo合金与Zr-4合金的扩散层性质进行了研究。三明治结构的U-Mo/Zr-4扩散偶在760~800℃下包覆热轧后,保温10~66 h。采用扫描电子显微镜(SEM)分析了扩散层的形貌和厚度,采用波谱仪(WDS)分析了各元素在扩散区内的分布情况,采用X射线衍射仪(XRD)测定了扩散层的相组成。分析结果表明,即使在800℃的高温下,U-Mo/Zr-4的扩散程度依然微弱,表现出良好的相容性;U-Mo/Zr的扩散层中间出现裂纹,裂纹两侧的扩散层相组成明显不同,靠近U-Mo侧为富Mo相,其主要是以化合物ZrMo_2为基的固溶体;靠近Zr-4侧的为富Zr相,其主要是以化合物UZr_2为基的固溶体;裂纹认为是由U和Zr不等量的原子交换所造成的。     

Heats of formation of (U,Mo)Al3 and U(Al,Si)3

The heats of formation of (U,Mo)Al₃ intermetallic compounds were obtained by measuring the reaction heats of U-Mo/Al dispersion samples by differential scanning calorimetry. Based on literature data for the reaction heats of U₃Si/Al and U₃Si₂/Al dispersion samples, the heats of formation of U(Al,Si)₃ as a function of the Si content were calculated. The heat of formation of (U,Mo)Al₃ becomes less negative as the Mo content increases. Conversely, the heat of formation of U(Al,Si)₃ becomes more negative with increasing Si content.     

Characterization of the reaction layer in U-7wt%Mo/Al diffusion couples

The reaction layer in chemical diffusion couples U-7wt%Mo/Al was investigated using optical and scanning electron microscopy, electron probe microanalysis and X-ray diffraction (XRD) techniques. When the U-7wt%Mo alloy was previously homogenized and the γ(U, Mo) phase was retained, the formation of (U, Mo)Al₃ and (U, Mo)Al₄ was observed at 580 °C. Also a very thin band was detected close to the Al side, the structure of the ternary compound Al₂₀UMo₂ might be assigned to it. When the decomposition of the γ(U, Mo) took place, a drastic change in the diffusion behavior was observed. In this case, XRD indicated the presence of phases with the structures of (U, Mo)Al₃, Al₄₃U₆Mo₄, γ(U, Mo) and α(U) in the reaction layer.     

Characterization of the interaction layer grown by interdiffusion between U-7wt%Mo and Al A356 alloy at 550 and 340 °C

U(Mo) alloys are under study to get a low-enriched U fuel for research and test reactors. Qualification experiments of dispersion fuel elements have shown that the interaction layer between the U(Mo) particles and the Al matrix behaves unsatisfactorily. The addition of Si to Al seems to be a good solution. The goal of this work is to identify the phases constituting the interaction layer for out-of-pile interdiffusion couples U(Mo)/Al(Si). Samples γU-7wt%Mo/Al A356 alloy (7.1 wt%Si) made by Friction Stir Welding were annealed at 550 and 340 °C. Results from metallography, microanalysis and X-ray diffraction, indicate that the interaction layer at 550 °C is formed by the phases U(Al,Si)₃, U₃Si₅ and Al₂₀Mo₂ U, while at 340 °C it is formed by U(Al,Si)₃ and U₃Si₅. X-ray diffraction with synchrotron radiation showed that the Si-rich phase, previously reported in the interaction layer at 550 °C near U(Mo) alloy, is U₃Si₅.     

Annealing behavior of ultrathin Mo layer located at interface or on surface of Ti－Si system

Annealing behavior,at different annealing temperatures,of an ultrathin Mo layer located between a Ti film and Si substrate or deposited on the top of surface of a Ti film was investigated by Rutherford backscattering spectrometry(RBS), cross-sectional transmission electron microscopy(TEM) and energy dispersive X-ray spectrometry(EDS),In a Ti/Mo/Si structure,partially reacted film with layer structure of Ti-rich silicide/TiSi2/(Mo,Ti) Si2 on a Si substrate was formed after 550℃ annealing for 30min.The ratio of Mo to Ti in(Mo,Ti)Si2 layer decreases from near Si substrate upwards and becomes zero at about 20nm away.In a Mo/Ti/Si structure, The surface Mo layer enhances the Si diffusion from the substrate during annealing.Mo bearing Ti rich silicide exists on the surface until 600℃ and then converts to (Mo,Ti )Si2 after 650℃ annealing,and the atomic ratio of Mo to Ti decreases from the top surface into Ti silicide film,and becomes zero at about 30nm away from the surface.In both cases of interface Mo and surface Mo layer,thd atomic ratio of Mo to Ti in the region of (Mo,Ti)Si2 was found to be very low,with an average value of less than 0.2.Low content of Mo in Mo containing ternary silicide leads easily to the formation of the stable phase of C54(Mo,Ti)Si2,which acts as a template for the formation of C54 TiSi2 beneath when Mo is deposited on the surface.     

Transmission electron microscopy characterization of irradiated U–7Mo/Al–2Si dispersion fuel

The plate-type dispersion fuels, with the atomized U(Mo) fuel particles dispersed in the Al or Al alloy matrix, are being developed for use in research and test reactors worldwide. It is found that the irradiation performance of a plate-type dispersion fuel depends on the radiation stability of the various phases in a fuel plate. Transmission electron microscopy was performed on a sample (peak fuel mid-plane temperature ～109 °C and fission density ～4.5 × 10²⁷ f m^?3) taken from an irradiated U–7Mo dispersion fuel plate with Al–2Si alloy matrix to investigate the role of Si addition in the matrix on the radiation stability of the phase(s) in the U–7Mo fuel/matrix interaction layer. A similar interaction layer that forms in irradiated U–7Mo dispersion fuels with pure Al matrix has been found to exhibit poor irradiation stability, likely as a result of poor fission gas retention. The interaction layer for both U–7Mo/Al–2Si and U–7Mo/Al fuels is observed to be amorphous. However, unlike the latter, the amorphous layer for the former was found to effectively retain fission gases in areas with high Si concentration. When the Si concentration becomes relatively low, the fission gas bubbles agglomerate into fewer large pores. Within the U–7Mo fuel particles, a bubble superlattice ordered as fcc structure and oriented parallel to the bcc metal lattice was observed where the average bubble size and the superlattice constant are 3.5 nm and 11.5 nm, respectively. The estimated fission gas inventory in the bubble superlattice correlates well with the fission density in the fuel.     

Irradiation behavior of ground U(Mo) fuel with and without Si added to the matrix

In the framework of the IRIS-TUM irradiation program, several full size, flat dispersion fuel plates containing ground U(Mo) fuel kernels in an aluminum matrix, with and without addition of silicon (2.1 wt.%), have been irradiated in the OSIRIS reactor. The highest irradiated fuel plate (with an Al-Si matrix) reached a local maximum burnup of 88.3% ²³⁵U LEU-equivalent and showed a maximum thickness increase of 323 μm (66%) but remained intact. This paper reports the post irradiation examination results obtained on four IRIS-TUM plates. The evolution of the fission gas behavior in this fuel type from homogeneously dispersed nanobubbles to the eventual formation of large but apparently stable fission gas bubbles at the interface of the interaction layer and the fuel kernel is illustrated. It is also shown that the observed moderate, but positive effect of Si as inhibitor for the U(Mo)-Al interaction is related to the dispersion of this element in the interaction layer, although its concentration is very inhomogeneous and appears to be too low to fully inhibit interaction layer growth.     

Post-irradiation examination of uranium-7 wt% molybdenum atomized dispersion fuel

Two low-enriched uranium fuel plates consisting of U-7wt%Mo atomized powder dispersed in an aluminum matrix, have been irradiated in the FUTURE irradiation rig of the BR2 reactor at SCK•CEN. The plates were submitted to a heat flux of maximum 353 W/cm² while the surface cladding temperature is kept below 130 °C. After 40 full power days, visual examination and profilometry of the fuel plates revealed an increase of the plate thickness. In view of this observation, the irradiation campaign was prematurely stopped and the fuel plates were retrieved from the reactor, having at their end-of-life a maximum burn-up of 32.8% ²³⁵U (6.5% FIMA). The microstructure of one of the fuel plates has been characterized in an extensive post-irradiation campaign. The U(Mo) fuel particles have been found to interact with the Al matrix, resulting in an interaction layer which can be identified as (U,Mo)Al₃ and (U,Mo)Al₄. Based on the composition of the interaction layer it is shown that the observed physical parameters like thickness of the interaction layer between the Al matrix and the U(Mo) fuel particles compare well to the values calculated by the MAIA code, an U(Mo) behavior modeling code developed by the Commissariat à l’énergie atomique (CEA).     

Microstructural characterization of U-7Mo/Al-Si alloy matrix dispersion fuel plates fabricated at 500 °C

The starting microstructure of a dispersion fuel plate will impact the overall performance of the plate during irradiation. To improve the understanding of the as-fabricated microstructures of U-Mo dispersion fuel plates, particularly the interaction layers that can form between the fuel particles and the matrix, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses have been performed on samples from depleted U-7Mo (U-7Mo) dispersion fuel plates with either Al-2 wt.% Si(Al-2Si) or AA4043 alloy matrix. It was observed that in the thick interaction layers, U(Al, Si)3 and U6Mo4Al43 were present, and in the thin interaction layers, (U, Mo) (Al, Si)3, U(Al, Si)4, U3Si3Al2, U3Si5, and possibly USi-type phases were observed. The U3Si3Al2 phase contained some Mo. Based on the results of this investigation, the time that a dispersion fuel plate is exposed to a relatively high temperature during fabrication will impact the nature of the interaction layers around the fuel particles. Uniformly thin, Si-rich layers will develop around the U-7Mo particles for shorter exposure times, and thicker, Si-depleted layers will develop for the longer exposure times.