UO_2-Zr弥散燃料板严重事故早期行为与熔融芯体迁移模型研究

基于UO2-Zr弥散燃料板的结构与材料特性,利用已有的扩散、Nb-Zr反应以及UO2-Zr等材料学相关文献研究了UO2-Zr弥散燃料板严重事故过程中的氧化、固相反应以及熔融物迁移等特殊过程的机理模型,能为含UO2-Zr弥散燃料板堆芯的严重事故行为特性研究与安全分析提供参考。     

多气泡对燃料颗粒应力分布的影响研究

利用有限元模拟方法建立了UO2弥散型燃料颗粒受内部多个气泡内压作用的模型,计算得到了燃料颗粒内部存在多个气泡时的应力分布结果。结果表明,当气泡沿x轴均匀排列时,y方向的最大正应力随气泡数量的增多而增大,且增大幅度逐渐减小,气泡对燃料颗粒内部最大正应力的影响存在极限;当存在多行气泡时,燃料颗粒内部x方向的最大正应力随气泡行数的增加而增大,y方向的最大正应力随气泡行数的增加而减小;气泡造成的燃料颗粒内部的应力集中效应随距径比的增大而减小。     

UAIx-AI弥散体的强度与UAIx含量的关系

直接测量了 UAl_x-Al 弥散型燃料元件板中燃料芯体的强度,研究了不同 UAl_x 含量对 UAl_x-Al弥散体强度的影响。实验结果与文献值进行了比较和讨论。     

气泡相互作用对燃料颗粒应力分布的影响

本工作建立了受气泡内压作用的双气泡UO2模型，利用有限元方法得到燃料颗粒受气泡内压作用、不同气泡间距条件下的燃料颗粒应力分布结果，并讨论了气泡间距、气泡半径和气泡内压对气泡之间相互作用的影响。研究结果表明，受气泡相互作用的影响，燃料颗粒内部产生了应力集中，应力集中倍率与气泡间距和气泡半径的比值（距径比）有关，与气泡内压无关。当距径比等于1时，应力集中倍率约为未考虑气泡相互作用影响时的2倍。当气泡尺寸不同时，应力集中主要发生在靠近小气泡的燃料基体处。     

弥散燃料颗粒裂纹起源的有限元模拟分析

通过建立含多气泡的燃料颗粒模型,采用有限元方法分析了燃料颗粒在裂变气体气泡内压作用下的应力分布,统计了燃料颗粒内部气泡位置对气泡内壁处的最大拉应力的影响,并结合实验结果探寻了弥散燃料颗粒在辐照后退火时的裂纹起源。结果表明:当弥散燃料颗粒内部含有多个裂变气体气泡时,受气泡内压作用,气泡内壁径向应力为压应力,环向应力为拉应力;气泡位置距燃料颗粒心部越远,气泡内壁处的最大环向拉应力越大;表层气泡的最大环向拉应力远大于心部气泡的;燃料颗粒裂纹起源于表层气泡内壁。     

UO2弥散型燃料辐照后高温失效时显微分析

对辐照后燃料板进行退火试验,用显微镜观察了UO2颗粒的微观形貌随着温度的升高的变化情况.在高温下裂变气体膨胀,在UO2颗粒内气孔贯通形成裂纹穿破涂层,引起UO2颗粒局部破碎脱落,UO2涂层外的反应层由于高温加剧的扩散反应还形成了明显的孔洞.     

弥散型燃料芯体结构的蒙特卡罗模拟(英文)

在研究堆中的辐照条件下，U3Si2-Al 弥散型燃料的燃料颗粒和基体界面发生相互扩散。由于相互扩散反应,在每个 U3Si2颗粒的周围形成 U3Al7Si2反应层。反应层厚度随辐照时间和裂变密度而增加。反应层的形成造成了 U3Si2燃料和铝基体的消耗。该过程导致燃料芯体几何结构的演化。根据弥散体中燃料的随机分布特点,作者采用蒙特卡罗方法发展了燃料芯体结构演化的模拟方法。每个颗粒的特性都可以用直径和位置来表示。芯体结构参数包括颗粒尺寸分布、制造状态下的燃料体积分数、反应层厚度、反应层体积、U3Si2燃料体积分数、铝体积分数、接触几率和颗粒相互连接分数。特别是对于制造状态下的燃料体积分数为 43%时,颗粒尺寸较好地服从正态分布。模拟了在 6 mm×6 mm×0.5 mm 的芯体体积中 13 000 个抽样颗粒的情况下,各芯体结构参数随反应层厚度从 0～16 μm 变化时的函数变化情况。     

IMF燃耗特性与次锕系核素产量分析

在轻水堆中采用惰性基质燃料(IMF)能有效地从源头上降低乏燃料中次锕系核素(MA)的含量。为了研究IMF的燃耗特性,选取两种典型IMF方案PuO2+ZrO2+MgO和PuO2+ThO2,开展不同PuO2含量下IMF燃耗反应性计算,并与UO2燃料以及MOX燃料进行比较分析。结果表明:在总燃耗时间为1 095d情况下,两种IMF方案中PuO2体积分数为2%~10%时,其寿期末kinf均大于1,但PuO2+ZrO2+MgO方案的燃耗反应性波动大于PuO2+ThO2方案,PuO2+ThO2方案燃料寿期末MA的含量明显小于前者;在同一等效重金属质量分数下,MOX、UO2燃料寿期末MA的含量均大于两种IMF。     

界面反应引起弥散型燃料的芯体结构演化

在反应堆运行工况下,Ｕ３Ｓｉ２－Ａｌ弥散型燃料的燃料颗粒与基体的界面相互扩散形成反应层,从而导致芯体结构的演化。本文根据Ｍｏｎｔｅ－Ｃａｒｌｏ原理建立了弥散型燃料芯体的模拟方法,并用该方法模拟了燃料相体积分散为４３％和具有一定尺寸分布的球形燃料颗粒在芯片中的空间随机排列。     

UO_2-多壁碳纳米管复合燃料芯块的制备工艺

分别采用热压烧结与无压烧结工艺制备了掺杂5%~20%多壁碳纳米管(MWNTs)的UO2复合燃料芯块,分析了芯块的性能。结果表明:乙醇湿法球磨可将MWNTs均匀分散到UO2基体中;热压烧结芯块随MWNTs含量的增加,芯块密度逐渐下降,MWNTs含量为5%的芯块密度为96.7%TD;无压烧结芯块随MWNTs含量的增加,芯块密度先升高后降低,MWNTs含量为12.5%的芯块密度最高,为97.2%TD;1 400℃、50 MPa热压烧结工艺,MWNTs与UO2基体未发生反应;1 750℃无压烧结工艺,MWNTs与UO2基体产生微弱反应生成少量UC相;SEM显示,MWNTs在UO2基体以沿晶和穿晶状态分布;在250℃,热压烧结UO2-10%MWNTs芯块热导率为6.76 W/(m·K),提高了20.28%;无压烧结UO2-12.5%MWNTs芯块热导率为6.65 W/(m·K),提高了18.33%。     

Composite materials and systems as alternative inert matrix fuel to dispose civil or weapon grade plutonium in light water reactors.

To complete the IMF cercer studies on the problem of Pu utilization in LWRs, a cermet fuel approach is presented. The advantages of cermet fuel are associated with high heat conductivity, ability to retain the fission products and a well-developed fabrication process. Attractive possibilities for the creation of new cermet fuels and cermet fuel elements are also presented. R&D activity aimed at the development of cermet fuel element with PuO₂-Zr composite was undertaken. As a result of this activity comparative analysis of thermodynamic calculations for UO₂-Zr and PuO₂-Zr composites was carried out, as well as an assessment of Pu loading and preliminary thermal calculations. As a consequence, it was concluded that the PuO₂-Zr cermet system could be considered as a possible variant of new cermet fuel and cermet fuel element for Pu burning in LWRs.     

An overview of reactivity initiated accident behavior of rock-like fueled pressurized water reactors

Reactivity initiated accident (RIA) analyses of plutonium rock-like oxide (ROX) fueled PWRs have been carried out with the point kinetics calculations. As a result, the analyses have shown a very severe transient behavior of the ROX fueled PWR, which is unacceptable without any improvement. It was also found that the RIA behavior of ROX fueled PWRs can be improved by increasing the negative fuel temperature coefficient (_f). For this improvement, the additives in the ROX fuel such as UO₂ and ThO₂ were considered, as well as a ROX assembly partial loading UO₂ core. With UO₂ additive, it was successful to have satisfying _f and RIA behavior of ROX fuel core, while the partial loading core must be further improved. Besides the ROX-PWR RIA analytical study, the actual behavior of the ROX fuel pin under RIA condition has been experimentally investigated at the Nuclear Safety Research Reactor (NSRR) of JAERI. Though the ROX fuel pin failure mechanism with fuel melting seems quite different from that of UO₂ pin with cladding melting, the ROX pin failure threshold was found to be roughly the same as that of UO₂ in terms of accumulated energy per unit fuel volume.     

离子液体中UO2(CMPO)3(NO3)2的组装及CMPO萃取铀的机理

离子液体具有独特的物理化学性质,可以参与或影响两亲分子自组装。离子液体介质中的自组装研究所涉及的两亲分子多为有机化合物,而金属配合物在离子液体中的组装鲜有报道。另外,萃取剂正辛基苯基-N,N-二异丁基胺基甲酰基甲基氧化膦(CMPO)在1-乙基-3-甲基咪唑双三氟甲基磺酰亚胺盐(C₂mimNTf²)中萃取UO₂⁺²时形成的萃合物结构组成有待深入研究。本工作探究了UO₂(CMPO)₃(NO₃)₂在C₂mimNTf²中的组装行为。原位透射电镜(原位TEM)研究表明:UO₂(CMPO)₃(NO₃)₂在C₂mimNTf²(含70μL水)中形成聚集体,冷冻刻蚀电镜(FF-TEM)显示该聚集体是胶束。此外,研究了CMPO-C₂mimNTf²体系萃取UO₂⁺²时形成的萃合物组成。离子色谱结果表明:萃取前后水相中NO^-₃浓度变化不大,电喷雾质谱(ESI-MS)上均为UO₂(CMPO)₃(NTf₂)₂的碎片离子峰,这些结果说明:CMPO-C₂mimNTf²体系萃取UO₂⁺²时形成的萃合物组成为UO₂(CMPO)₃(NTf₂)₂而非UO₂(CMPO)₃(NO₃)₂。这有助于深入了解金属配合物在离子液体中的组装行为,并对理解CMPO-C₂mimNTf²体系萃取UO₂⁺²的机理提供了重要参考。     

UO2燃料燃耗对高放废物管理的影响研究

从乏燃料的不同燃耗引起放射性和化学组成的变化出发,分析乏燃料经后处理后的衰变热、Mo及贵金属含量对玻璃固化工艺和玻璃固化体储存的影响,计算得到了不同燃耗乏燃料制得的高放玻璃的数量。计算结果认为：对于冷却8 a的乏燃料,决定玻璃固化体包容量的不是高放主组分的热功率;对于燃耗小于40 GW•d/tU的乏燃料,决定玻璃固化体包容量的是Mo元素含量;当燃耗大于45 GW•d/tU时,贵金属含量成为决定玻璃固化体包容量的主要因素,同时UO₂燃料燃耗与高放玻璃固化体数量上存在线性关系,燃耗增加会导致高放废物玻璃固化体数量增加。随着燃耗的增加,以Mo含量及贵金属含量计算得到的玻璃固化体数量比以衰变热计算得到的玻璃固化体数量多,因此,高放废物玻璃固化前将Mo及贵金属进行分离有利于减少高放废物玻璃固化体数量。对于UO₂燃料,燃耗加深对于高放废物玻璃固化体暂存时间几乎无影响。     

Dynamics aspects of plutonium burning in an inert matrix

Burnup calculations have been performed on a mini fuel assembly containing 21 fuel rods and four water holes at the corners. The fuel rod positions were filled with 4% enriched UO₂ fuel and with either reactor grade or weapons grade plutonium mixed in an inert matrix. The ratio between the UO₂ and the IMF rods was varied to investigate the influence of the UO₂ fuel on the dynamics of the assembly. From a simple reactor model with one delayed neutron group and first-order fuel and temperature feedback mechanisms, the linear transfer function from reactivity to reactor power was calculated that was subsequently used in a root-locus analysis. From this, it is concluded that only 20% of the fuel rods need to be made of UO₂ to have a fuel that is linearly stable up to 1000 days of irradiation.     

Rock-like oxide fuel behavior under reactivity initiated accident conditions

Pulse irradiation tests of two types of rock-like oxide (ROX) fuel, i.e. yttria stabilized zirconia (YSZ) and YSZ/Spinel composite, were conducted in the Nuclear Safety Research Reactor (NSRR) to investigate the fuel behavior under reactivity-initiated accident conditions. The ROX fuels failed with cladding burst at fuel volumetric enthalpies above 10 GJ m⁻³, which was comparable to that of UO₂ fuel. The failure of the ROX fuels, however, occurred with considerable fuel melting and was quite different to that of UO₂ fuel, which was caused by cladding melting and embrittlement due to heavy oxidation. Lower fuel melting temperature of the ROX fuels compared to that of UO₂ contributed to the different fuel failure modes. Certain amount of molten ROX fuel dispersed out at the failure. However, the mechanical energy generation due to the molten fuel/water interaction was negligible for the ROX fuels at peak fuel enthalpies below 12 GJ m⁻³.     

UO2复合燃料芯块导热性能有限元模拟

目前各国均在开发适用于压水堆的含有高导热性第二相材料的新型先进UO₂复合燃料芯块。本文通过有限元计算方法分析了新型先进UO₂复合燃料芯块关键结构参数对其导热性能的影响。结果表明：少量高导热性第二相材料的添加可显著降低燃料芯块服役过程中的中心线温度;第二相的种类、含量、分布形式等均对新型先进UO₂复合燃料芯块的导热性能有重要影响。