RELAP/SCDAPSIM/MOD4.0程序的FHR应用扩展及验证

基于轻水堆最佳估算系统分析程序RELAP/SCDAPSIM/MOD4.0,添加新的FLi Na K熔盐热物性参数和适用于熔盐的对流换热系数,开发了适用于FHR系统的热工水力分析程序RELAP5-FHR。通过FLi Na K高温熔盐实验回路对RELAP5-FHR程序进行实验验证。结果表明:RELAP5-FHR程序计算值与实验值吻合较好,验证了程序的适用性。     

FKZr的热物性及热稳定性研究

熔盐堆冷却剂的热物性是熔盐堆物理、热工水力学设计以及安全分析的重要参数。KF-ZrF4(58-42 mol%)(FKZr)是熔盐堆中的一个具有潜在应用价值的冷却剂。该组成熔盐的热物性在文献中鲜有报道,这为其实际应用带来困难。分别采用差示扫描量热(Differential Scanning Calorimetry,DSC)、阿基米德和热重分析等方法测量和表征了FKZr熔盐的熔点、熔化焓、密度等重要的热物性参数和热稳定性。实验结果表明FKZr的熔点为693.6 K,与文献报道结果一致,符合熔盐堆中冷却剂的要求;熔化焓为71.8 J·g?1;密度为??3.3841?0.8954?10?3T(753?923 K);热重分析表明FKZr在873 K下性质稳定,不发生明显的挥发现象。     

工质替代FLiBe研究涡流二极管单向特性的模化分析

涡流二极管作为氟盐冷却高温堆(Fluoride-salt-cooled High-temperature Reactor,FHR)非能动余热排出系统的关键设备,其单向性将影响FHR事故工况下排出堆芯余热的能力和正常工况时堆芯的热损失。为了研究在冷却剂FLi Be熔盐工质下涡流二极管的单向特性,并解决FLi Be较强腐蚀性、高熔点直接进行实验难度较大及成本较高的问题,本文采用比较安全和便于实验的水、#22透平油和HTS-1作为FLi Be的替代工质,通过相似理论进行流体模化,并采用数值模拟方法研究模化方法的可行性。结果表明:采用HTS-1、水和#22透平油工质代替FLi Be研究相同结构尺寸涡流二极管内的单向特性是可行的。HTS-1模化FLi Be在涡流二极管内流动可实现完全相似,水和#22透平油模化FLi Be可实现部分相似。通过数值模拟初步验证部分相似模化方法是可行的。     

FLiNaK熔盐中CsF的蒸发与分离

Cs的同位素是核裂变的主要产物之一,在熔盐反应堆液态燃料盐中以Cs F的化学形态存在,定期从燃料盐中除去或减少其含量将有助于提高反应堆的中子经济性。本文用FLi Na K熔盐模拟熔盐堆载体盐FLi Be体系,研究了Cs F在不同蒸发条件下的蒸发行为,并尝试进行了减压蒸馏和金属Li还原蒸发技术分离Cs F的实验研究。研究表明,在5 Pa蒸馏压力下,Cs F的蒸发量随温度呈线性上升趋势,780oC时Cs F的含量由1%降到0.14%,分离率达86%,但此时载体盐的蒸发量达9.5%;在常压、700oC条件下,熔盐中Cs F的蒸发比例随还原剂Li的添加量而提高,当添加的金属Li的摩尔浓度与Cs F为120:1时,Cs F分离率达91%。研究结果为了解Cs F在氟盐体系中的蒸发行为和建立可行的分离方法提供基础实验依据。     

不同Cr含量的镍基高温合金在LiF-NaF-KF熔盐中的腐蚀行为

为探究不同Cr含量的镍基合金在熔盐环境中的腐蚀行为,在700°C的FLi Na K(Li F-Na F-KF:46.5-11.5-42 mol%)盐中对Hastelloy B-2、Haynes 242、Hastelloy S、GH3030和Hastelloy X五种不同Cr含量的镍基高温合金进行了400 h的腐蚀实验。利用扫描电子显微镜(Scanning Electron Microscope,SEM)和电子探针(Electron Probe Microanalysis,EPMA)对腐蚀后样品进行表征,结合样品失重,对不同Cr含量合金的腐蚀规律进行归纳分析。结果表明,合金的耐腐蚀性能受其Cr含量的影响较大,低Cr合金(Hastelloy B-2和Haynes 242)具有较好的耐熔盐腐蚀性能,高Cr合金耐熔盐腐蚀性能较差,当合金中Cr含量大于20%时(GH3030和Hastelloy X),腐蚀急剧增加,合金表面出现明显的贫Cr层,合金不适合在熔盐环境中应用。     

基于气动悬浮的高温氧化物熔体热物性测量

堆芯熔融物的热物性是研究反应堆严重事故进程及堆内堆外现象机理的重要基础参数。当堆芯熔化时，堆内温度达3 000 K,形成U-Zr-O-Fe多元混合物，而气动悬浮技术是优选的高温下测量堆芯熔融物基础热物性的技术。本文描述了一套基于气动悬浮和激光加热技术的密度、表面张力和黏度的测量装置，目前已实现高温氧化物密度的实验测量。装置采用收缩-扩张型锥形喷嘴悬浮球状样品，采用CO₂连续激光器加热并熔化样品，采用双色红外测温仪监测样品的温度并进行激光器功率反馈控制；采用高速相机记录样品轮廓的变化，并结合图像分析法计算样品的体积，最后得到被测材料在高温下的密度。实验测量得到2 750～3 200 K范围内氧化锆熔体的密度，其在熔点(2 988 K)处的密度为4.717 g/cm~3,温度系数为-7.202×10^-4 g/(cm~3·K)。     

熔盐冷冻壁传热平衡数值模拟及实验研究

在熔盐堆燃料干法处理流程中,处理设备面临着严重的材质腐蚀问题。熔盐冷冻壁技术被视为保护相关设备耐受化学腐蚀的有效方法。熔盐冷冻壁厚度及温度场分布对防护效果及相关干法工艺参数有重要影响,在中心冷却式冷冻壁实验装置上采用FLi Na K熔盐介质开展了冷冻壁维持的实验研究,采用中心冷棒空气冷却的方式得到了不同壁温下冷冻壁的厚度范围及反应釜内温度场分布。结合数值模拟计算了冷冻壁的传热平衡工况,并与实验值进行对比和分析,得到了较为适宜的冷冻壁厚度的调节工况。冷冻壁厚度控制工艺和釜内温度场分布可为冷冻壁工艺容器的设计提供参考。     

熔盐燃料对加速器驱动的次临界堆中子学性能的影响

加速器驱动的次临界熔盐堆(Accelerator-Driven Subcritical Molten Salt Reactor,ADS-MSR)结合了熔盐堆与ADS的许多优点,在先进核燃料利用方面有独特的优势。为了研究熔盐燃料的使用对ADS系统堆芯的中子学性能的影响,基于MCNP(Monte Carlo N Particle Transport Code)程序,分别计算并分析了熔盐燃料对加速器驱动的次临界堆的外源质子效率、中子能谱以及钍铀转换比等参数的影响。结果表明:相较于氧化物燃料,熔盐燃料的使用将会增加对外源中子和裂变中子的慢化,并且会提高堆芯的入射质子效率。同时,由于熔盐燃料的慢化效应,FLi Be和FLi熔盐燃料燃耗初期的钍铀转换比(CR)分别为1.023和1.062,略低于氧化物燃料的1.068。另一方面,熔盐燃料的在线处理会极大降低燃耗过程中的反应性损失。通过在线燃料处理和在线添料,FLi熔盐和FLi Be熔盐燃料的CR分别在燃耗运行的第1年和第3年超过氧化物燃料,并且能够长期稳定在1.06和1.00左右。     

HYSYS软件应用于熔盐冷却系统瞬态分析的可行性研究

系统软件对熔盐堆冷却剂系统的整体模拟、瞬态分析和安全研究起到至关重要的作用。针对化工领域系统仿真软件HYSYS进行二次开发,植入熔盐物性,修改熔盐换热模型,利用软件已有模型(等效回路加热器模型)尝试分析其对熔盐冷却系统仿真的可行性。为验证修改后的软件的可靠性,对中国科学院上海应用物理研究所钍基核能中心硝酸盐熔盐(KNO3-NaNO2-NaNO3 Molten Salt,HTS)实验装置进行了系统仿真模拟,并与实验结果进行了对比。结果显示,扩展后的软件对熔盐冷却系统的分析研究具有较好的适用性。     

纳米TiO_2增强NaNO_3-KNO_3-NaNO_2熔盐的中温储热特性

NaNO_3-KNO_3-NaNO_2(Hitec)熔盐作为一种理想的中高温传储热介质,未来有望在太阳能热利用等领域展开广泛应用。但其作为中温储热介质而言,其比热和导热性能相对较低,若能提高其比热和导热系数无疑将在太阳能热利用等实际应用中具有很重要的意义。采用水法技术制备了纳米TiO_2/Hitec熔盐复合储热介质,采用不同的表征技术研究了不同粒径、不同添加量纳米TiO_2颗粒对复合储热介质的比热、导热系数和热稳定性的影响。结果表明:与Hitec熔盐相比,纳米TiO_2颗粒明显提高了熔盐复合储热介质的储热特性。其中25 nm粒径,添加质量分数为0.062 5%纳米TiO_2对Hitec熔盐复合储热介质的比热(提高12%)和导热系数(增大15%)增强显著,同时热稳定性也得到改善。     

The effect of corrosion product CrF3 on thermo-physical properties of FLiNaK

FLiNaK (LiF–NaF–KF: 46.5–11.5–42 mol %) is a promising candidate as the secondary loop coolant in molten salt reactor. The thermo-physical properties of pure FLiNaK and FLiNaK containing up to 6000 ppm (equivalent to mg/kg) corrosion product CrF₃ were measured. The results indicate that the effects of CrF₃ on melting point, enthalpy, specific heat capacity, density and thermal diffusivity of FLiNaK in liquid state are negligible within the allowable error range, meanwhile the change of thermal diffusivity is significant for FLiNaK in solid state. This work provides fundamental knowledge for the thermo-physical properties of coolant in molten salt reactor.     

钍基熔盐堆核能系统中熔盐的蒸馏纯化与分离

氟盐具有化学与辐射稳定性高、热容量大、传热性能好、运行温度高和蒸汽压低等优点,被用作熔盐堆的燃料载体和冷却剂。随着熔盐堆技术的发展,开发熔盐的净化、回收工艺非常必要。熔盐减压蒸馏技术基于物质挥发性差异进行组分分离,由于过程操作简单、不引入新的物质等特点,在燃料处理过程中有广泛应用。利用减压蒸馏技术对钍基熔盐堆核能系统的载体盐回收、电解产物纯化、模拟燃料球去除浸渗熔盐等方面进行了研究。研究结果表明,含CsF、SrF_2、LaF_3和ThF_4的FLiNaK盐经减压蒸馏处理,可从FLiNaK中除去SrF_2和LaF_3,去污因子分别为4.4×10~3和1.9×10~3,Th的去污因子为94;通过蒸馏可去除电解产物表面夹带的氟盐,纯化电解产物;燃料球中浸渗熔盐在1 085℃下处理37h可去除石墨球中94%的浸渗熔盐。     

Corrosion behavior of Hastelloy-N alloys in molten salt fluoride in Ar gas or in air

The effects of air on the corrosion of Hastelloy-N alloys in molten salt coolant containing fission product elements were investigated to determine the safety of structural materials in high-temperature reactors cooled with fluoride salt. Corrosion tests of Hastelloy-N in the molten fluoride salt FLiNaK in an alumina crucible and a graphite crucible under argon gas or air were performed at 773–923 K for 100 h. The depth of corrosive attack, as well as the extent of chromium and molybdenum depletion, increased with increasing temperature. The extent of Hastelloy-N corrosion in molten salt under air was significantly greater than under argon gas. The effect of adding the impurity cesium iodide to molten salt containing nuclear waste fuel on the corrosion behavior was negligible.     

Modeling oxidic molten core-concrete interaction in WECHSL

The WECHSL code aims at modeling the physical and chemical phenomena governing the molten core-concrete interaction in a severe reactor accident, when the molten core has penetrated the pressure vessel. Attention has recently been drawn to the influence of the melt properties, among others of the viscosity of oxidic melts, on the heat transfer, and on the melt behavior during MCCI. In the first step, the viscosity model in WECHSL was changed in order to better fit the experimental viscosities. To take into account the variation of the viscosity with temperature, an iterative scheme has been introduced in WECHSL to determine the gradient from the pool bulk temperature to the interface temperature in the melt boundary layer. In addition, the influence of porosity of the melt on the thermal conductivity was modeled. Finally, a method was implemented to correct the heat transfer relations. In this paper the WECHSL code including the above modifications is applied to a PWR accident scenario.     

The protective performance of a molten salt frozen wall in the process of fluoride volatility of uranium

The fluoride volatility method(FVM) is a technique tailored to separate uranium from fuel salt of molten salt reactors. A key challenge in RD of the FVM is corrosion due to the presence of molten salt and corrosive gases at high temperature. In this work, a frozen-wall technique was proposed to produce a physical barrier between construction materials and corrosive reactants.The protective performance of the frozen wall against molten salt was assessed using FLiNaK molten salt with introduced fluorine gas, which was regarded as a simulation of the FVM process. SS304, SS316 L, Inconel 600 and graphite were chosen as the test samples. The extent of corrosion was characterized by an analysis of weight loss and scanning electron microscope studies. All four test samples suffered severe corrosion in the molten salt phase with the corrosion resistance as: Inconel 600 SS316 L graphite SS304. The presence of the frozen wall could protect materials against corrosion by molten salt and corrosive gases, and compared with materials exposed to molten salt, the corrosion rates of materials protected by the frozen wall were decreased by at least one order of magnitude.     

氧化物沉淀-减压蒸馏耦合分离FLiNaK熔盐中的NdF_3

利用氧化物沉淀-减压蒸馏耦合法研究FLiNaK熔盐体系中氟化物的蒸发行为及稀土Nd的分离。高温下氧化物CaO与稀土氟化物NdF_3反应形成难溶于熔盐的稀土氧化物,通过减压蒸馏蒸发、收集冷凝FLiNaK熔盐,提高稀土与熔盐的分离度,促进熔盐的回收利用。研究表明,含有NdF_3(w=3%)的FLiNaK熔盐中加入CaO,730°C下反应6 h,n(NdF_3):n(CaO)=1:3时NdF_3的转化率达95%。X射线衍射(X-ray Diffraction,XRD)分析表明生成的Nd_2O_3主要沉淀在熔盐的底部。经730°C高温沉淀、930°C熔盐蒸馏,冷凝盐中稀土Nd的去污因子达9.4′105,而未经沉淀处理Nd的去污因子为3.1′104,表明高温沉淀蒸馏耦合法使稀土NdF_3转化为氧化物Nd_2O_3,显著增大稀土与FLiNaK的分离度,提高收集盐的纯度。     

氟化物熔盐体系中碘元素含量测定

使用NaClO氧化-电感耦合等离子体质谱(ICP-MS)分析技术测定了氟化物熔盐中碘元素含量,拟用于模拟熔盐反应堆环境中碘的行为研究。结果表明:含CsI的FLiNaK熔盐经NaClO氧化前处理,可使用ICP-MS有效测量其中的碘含量(以IO^-₃形式存在的碘),当FLiNaK盐取样量为0.1 g时,方法检出限为0.066μg/g,加标回收率为103.1%~104.3%,相对标准偏差(s r)<6%(n=6)。使用该方法与直接使用离子色谱法测量的结果一致,且该方法具有测量速度更快、检出限更低的优势,证实NaClO氧化-ICP-MS测量法可用于氟化物熔盐中低含量碘的有效测量。     

基于TREND程序的石墨通道液态熔盐堆无保护反应性引入事故初步分析

采用自编系统分析程序TREND,基于液态点堆动力学模型,针对10 MW石墨通道液态熔盐堆的设计,研究分析不同反应性在阶跃引入和线性引入情况下10 MW石墨通道液态熔盐堆堆芯功率、石墨温度和堆芯出口熔盐温度的瞬态变化。结果表明,阶跃引入低于570pcm（1pcm=10?5）反应性,堆系统能在无保护的情况下安全运行;当单根控制棒失提引入约800pcm时,反应性引入速率不超过8pcm/s,反应堆能够利用自身的温度、功率负反馈特性有效地控制功率峰值和降低堆芯出口温度,保证反应堆在无保护情况下安全运行。因此,液态熔盐堆具有良好的固有安全性。      

Influences of 7Li enrichment on Th-U fuel breeding for an Improved Molten Salt Fast Reactor (IMSFR)

The molten salt fast reactor (MSFR) shows great promise with high breeding ratio (BR),large negative temperature coefficient of reactivity,high thermal-electric conversion efficiency,inherent safety,and online reprocessing.Based on an improved MSFR optimized by adding axial fertile salt and a graphite reflector,the influences of 7Li enrichment on Th-U breeding are investigated,aiming to provide a feasible selection for the molten salt with high fissile breeding and a relatively low technology requirement for 7Li concentration.With the self-developed molten salt reactor reprocessing sequence based on SCALE6.1,the burn-up calculations with online reprocessing are carried out.Parameters are explored including BR,233U production,double time (DT),spectrum,6Li inventory,neutron absorption,and the tritium production.The results show that the 7Li enrichment of 99.95％ is appropriate in the fast fission reactor.In this case,BR above 1.10 can be achieved for a long time,corresponding to the 233U production of 130 kg per year and DT of 36 years.After 80 years' operation,the tritium production for 99.5％ is only about 7 kg,and there is no obvious increase compared to that for 99.9995％.