Experimental study of high temperature particle dropping in coolant liquid

A series of experiments of the premixing stage of fuel-coolant interactions (FCI), namely the particles falling into water, were carried out. The force on the particles during the course of falling has been studied. The dropping character of hot particle was influenced by three main parameters, i.e., particle temperature, particle diameter and coolant subcooling that varied over a wide range. A high-speed camera recorded the falling speed of the particle and the moving curves were obtained. The experimental results showed that for the film boiling on the surface of particle and water, the temperature increase of either particle or coolant would slow down the particle falling velocity. The falling velocity of particle in small diameter is lower than that of the bigger particle. The present work can provide an experimental foundation for further investigation of high-speed transient evaporation heat transfer.     

The result of a wall failure in-pile experiment under the EAGLE project

The WF (wall failure) test of the EAGLE program, in which 2 kg of uranium dioxide fuel-pins were melted by nuclear heating, was successfully conducted in the IGR (Impulse Graphite Reactor) of NNC/Kazakhstan. In this test, a 3 mm-thick stainless steel (SS) wall structure was placed between fuel pins and a 10 mm-thick sodium-filled channel (sodium gap). During the transient, fuel pins were heated, which led to the formation of a fuel-steel mixture pool. Under the transient nuclear heating condition, the SS wall was strongly heated by the molten pool, leading to wall failure. The time needed for fuel penetration into the sodium-filled gap was very short (less than 1 s after the pool formation). The result suggests that molten core materials formed in hypothetical LMFBR core disruptive accidents have a certain potential to destroy SS-wall boundaries early in the accident phase, thereby providing fuel escape paths from the core region. The early establishment of such fuel escape paths is regarded as a favorable characteristic in eliminating the possibility of severe re-criticality events. A preliminary interpretation on the WF test results is presented in this paper.     

Improvements of evaporation drag model

A special visible experiment facility has been designed and built, and an observable experiment is performed by pouring one or several high-temperature particles into a water pool in the facility. The experiment result has verified Yang‘s evaporation drag model, which holds that the non-symmetric profile of the local evaporation rate and the local density of vapor would bring about a resultant torce on the hot particle so as to resist its motion. However, in Yang‘s evaporation drag model, radiation heat transfer is taken as the only way to transfer heat from hot particle to the vapor-liquid interface, and all of the radiation energy is deposited on the vapor-liquid interface and contributed to the vaporization rate and mass balance of the vapor film. In improved model heat conduction and heat convection are taken into account. This paper presents calculations of the improved model, putting emphasis on the effect of hot particle‘s temperature on the radiation absorption behavior of water.     

A Numerical Analysis of Molten Metal Drop and Coolant Interaction

The interaction of molten metal drop and coolant is numerically analyzed to investigate the mechanism of fragmentation in vapor explosion. The numerical study is carried out by using a developed simulation code based on multi-phase thermal hydraulic model, which includes physical phenomena required for the analysis: heat transfer, mass change, liquid evaporation and treatment of surface. Several computational techniques are also implemented to improve the efficiency and stability of the numerical scheme. The obtained numerical results show that the growth of spikes on the molten metal drop surface is similar to that observed in Ciccarelli's experiment. The numerical study suggests that quick growth of spikes is the essential mechanism of fragmentation, which is caused by Taylor instability.     

Experimental and computational study on jet final depth under coolant jet-melt interaction

Pouring coolant into molten material provides an efficient method for cooling molten core debris in light water reactor. This coolant jet-melt interaction mode needs to be studied for proposed application and safety concern. The jet breakup pattern and its final depth are crucial factors for efficient cooling. In the present study, the hydraulic penetration behavior of coolant jet is investigated using experimental and numerical approaches. A series of visual experiments are conducted using low-density gasoline as coolant jet and high-density water as molten fuel. The images of jet behaviors and the data of gasoline jet penetration depth are obtained and analyzed. Based on FLUENT15.0 a 3D axisymmetric model is built and Volume of Fluid (VOF) method is used. The hydraulic penetration behaviors of jet and final penetration depth are correctly simulated and analyzed. The fluctuating phenomenon of penetration depth and the effects of various parameters are discussed. Jet velocity and density ratio are key factors to final penetration depth. The conclusions are helpful to understand the parameter influence and the fluctuation mechanism of final penetration depth and substantiate the understanding of the coolant jet hydraulic penetration behavior during coolant jet-melt interaction.     

高矿化度油藏聚合物基微泡沫驱油体系优化

针对某高矿化度油藏采用常规化学剂不抗盐,提高采收率难度大的问题,在高矿化度油藏条件下,以泡沫综合指数(FCI)筛选了两种起泡性好的表面活性剂TSS(12-2-12)-2OH和Triton X-100。在此基础上,优化了聚合物基微泡沫驱油体系中的起泡剂浓度、助起泡剂浓度和泡沫稳泡剂浓度,得到了最佳的聚合物基微泡沫驱油体系0.2%(w)TSS(12-2-12)-2OH+0.1%(w)Triton X-100+0.150%(w)KY5S+地层水。为高矿化度油藏提高采收率提供一条新的途径。     

Predicting ambulatory function following lower extremity trauma using the functional capacity index

This study evaluated the accuracy of experts’ predictions of ambulatory function following lower extremity trauma using the Functional capacity index (FCI). Data from three orthopedic trauma studies designed to determine long-term function following specific types of lower extremity injuries were used to examine the extent of agreement between the reported and predicted ambulatory function of 921 subjects. Functional limitations reported by the cohort using a generalized health status measure and more detailed questions on lower extremity function were compared with those predicted by experts based on the injuries sustained. The overall agreement between predicted and self-reported FCI function for ambulation was relatively low (31%). In the majority of cases (80%), the disagreement differed by one functional level. Subjects were more likely to report worse function than predicted by the experts. Multivariate modeling identified different injuries, combinations of injuries, and patient characteristics that significantly influenced agreement. For example, subjects who sustained both a tibia and a femur fracture were three times more likely than subjects who did not sustain either fracture type to report poorer ambulatory function than predicted. Many challenges are faced in predicting long-term function following trauma. More empirical data are needed to inform the process. These data suggest that until the FCI can more accurately predict long-term ambulatory function following different lower extremity injuries, it should not be used for this purpose.     

A Thermal Fragmentation Model Induced by Surface Solidification

A fragmentation phenomenon of a melt droplet induced by surface solidification has been studied for many years, but the fragmentation rate model, based on such a thermal mechanism, is not available for numerical simulation tools. In this study, in order to develop a fragmentation rate correlation of a melt droplet, induced by surface solidification, a thermal fragmentation mechanism is proposed, based on the Taylor instability. The theoretical fragmentation model is developed and a simplified non-dimensional correlation is proposed for convenient application to simulation tools. The developed fragmentation rate correlation is verified by simulating the MIXA experiment.     

Small-scale Experiment on Subcooled Water Jet Injection into Molten Alloy by Using Fluid Temperature-Phase Coupled Measurement and Visualization

The plunging water jet behavior into a pool of a molten lead-bismuth alloy is experimentally investigated. The mixing and interactions of fluids were detected by measuring the fluid temperature as well as the fluid phase distinction by the newly developed bifunctional probes.

In general knowledge of fuel-coolant interactions, the film boiling of water is caused immediately after the first contact of high-temperature melt and water, but the vapor film is locally collapsed by some reasons and the direct contact is extensively propagating in some cases which may produce the explosive vapor generation. In the melt-injection mode previously investigated by numerous researchers, the triggering of explosive interactions is considered as a local rewetting caused by instabilities of the vapor film as the melt temperature decrease. In the coolant-injection mode discussed by the present study, on the other hand, the water temperature poured into bulk melt continues to rise for penetration, in general, that should be effective to stabilize the film boiling. The present experiments showed, however, that the explosive boiling occurred in a condition that both water and melt initial temperatures were high enough for maintaining stable film boiling on the melt-water interface that is clearly different manner of the melt injection mode. Such unstable phenomena are observed when the instantaneous interfacial contact temperature exceeds the homogeneous nucleation temperature of water and the amount of saturated water is accumulated in a melt pool.     

基于模糊聚类迭代模型的洪灾评估标准计算方法

对于洪灾评估工作来说,制定一个具有普适性的洪灾等级评估标准是很重要的,而目前缺少一个被公开认可的标准制定方案。在模糊聚类迭代模型的基础上,提出了一种不受时空分布影响的洪灾评估标准计算方法。在求解目标函数时,采用混沌文化进化算法进行了优化。以四川省1976-2006年洪灾样本为例,计算出了四川省洪灾的标准化等级评估标准,并进行了验证。分析表明:该标准是合理有效并符合洪灾分布特点的,可以作为其它模型的评估标准。采用相对值标准,不受时空分布不同的影响,可以用于所有具有同一范围级别和较完备历史灾情数据的洪灾评估标准工作。