INVESTIGATION ON EFFECTS OF ENLARGED PIPE RUPTURE SIZE AND AIR PENETRATION TIMING IN REALSCALE EXPERIMENT OF SIPHON BREAKER

To ensure the safety of research reactors, the water level must be maintained above the required height. When a pipe ruptures, the siphon phenomenon causes continuous loss of coolant until the hydraulic head is removed. To protect the reactor core from this kind of accident, a siphon breaker has been suggested as a passive safety device. This study mainly focused on two variables: the size of the pipe rupture and the timing of air entrainment. In this study, the size of the pipe rupture was increased to the guillotine break case. There was a region in which a larger pipe rupture did not need a larger siphon breaker, and the water flow rate was related to the size of the pipe rupture and affected the residual water quantity. The timing of air entrainment was predicted to influence residual water level. However, the residual water level was not affected by the timing of air entrainment. The experimental cases, which showed the characteristic of partical sweep-out mode in the separation of siphon breaking phenomenon [2], showed almost same trend of physical properties.ungraded1111Ysciescopu

Experimental and numerical study for a siphon breaker design of a research reactor

For guaranteeing the pool water inventory, which is important to the nuclear safety of a research reactor, a siphon breaker is installed to limit the pool water drain during and after all postulated initiating events in the research reactor. Because the main pipe size of the reactor is relatively large, the size of the siphon break line should be determined to break the siphon phenomena. The siphon breaker design is validated through experiments and numerical simulations. An experimental loop was manufactured at a similar scale of a common research reactor, and a commercially available CFD code was used to compare the experimental results. The undershooting height was measured with a camera and absolute pressure transducer according to the siphon break line sizes. The pressure and superficial velocity inside the main pipe according to the pool water level were analyzed to understand the siphon break phenomena. The CFD code was tested to determine its usefulness for simulating siphon break phenomena over the same conditions with the experiment using several models for the two-phase flow phenomena. The undershooting height, pressure, and liquid superficial velocity were calculated using homogeneous and inhomogeneous models with the SST turbulent model and compared with the experimental results. Although the results of the ANSYS CFD model show some differences with the experimental data, the CFD results using the inhomogeneous model show good agreement with the experimental data. In addition, the homogeneous model results can be used conservatively in the design of a siphon breaker. (C) 2012 Elsevier Ltd. All rights reserved.X117sciescopu

INVESTIGATION ON EFFECTS OF ENLARGED PIPE RUPTURE SIZE AND AIR PENETRATION TIMING IN REAL-SCALE EXPERIMENT OF SIPHON BREAKER

To ensure the safety of research reactors, the water level must be maintained above the required height. When a pipe ruptures, the siphon phenomenon causes continuous loss of coolant until the hydraulic head is removed. To protect the reactor core from this kind of accident, a siphon breaker has been suggested as a passive safety device. This study mainly focused on two variables: the size of the pipe rupture and the timing of air entrainment. In this study, the size of the pipe rupture was increased to the guillotine break case. There was a region in which a larger pipe rupture did not need a larger siphon breaker, and the water flow rate was related to the size of the pipe rupture and affected the residual water quantity. The timing of air entrainment was predicted to influence residual water level. However, the residual water level was not affected by the timing of air entrainment. The experimental cases, which showed the characteristic of partical sweep-out mode in the separation of siphon breaking phenomenon [2], showed almost same trend of physical properties

A combined approach for high-performance Li–O2 batteries: A binder-free carbon electrode and atomic layer deposition of RuO2 as an inhibitor–promoter

A rechargeable lithium–oxygen (Li–O2) battery is considered as a promising technology for electrochemical energy storage systems because its theoretical energy density is much higher than those of state-of-the-art Li-ion batteries. The cathode (positive electrode) for Li–O2 batteries is made of carbon and polymeric binders; however, these constituents undergo parasitic decomposition reactions during battery operation, which in turn causes considerable performance degradation. Therefore, the rational design of the cathode is necessary for building robust and high-performance Li–O2 batteries. Here, a binder-free carbon nanotube (CNT) electrode surface-modified by atomic layer deposition (ALD) of dual acting RuO2 as an inhibitor–promoter is proposed for rechargeable Li–O2 batteries. RuO2 nanoparticles formed directly on the binder-free CNT electrode by ALD play a dual role to inhibit carbon decomposition and to promote Li2O2 decomposition. The binder-free RuO2/CNT cathode with the unique architecture shows outstanding electrochemical performance as characterized by small voltage gaps (∼0.9 V) as well as excellent cyclability without any signs of capacity decay over 80 cycles

Experimental study of siphon breaking phenomenon in the real-scaled research reactor pool

Pipe rupture is one of the main causes of loss-of-coolant accident (LOCA). A siphon-breaking system would provide a passive mean of preventing LOCA, increasing the safety of research reactors. But despite the need for such a system, previous research on siphon breaking has not been conducted in a systematic manner. In this study, specific lines and holes were selected to act as siphon breakers, and the effect of size and other variables were investigated using an experimental facility similar on the scale of a real reactor. The performance of various siphon breakers was evaluated experimentally for different siphon-breaker sizes, pipe-rupture points, and pipe-rupture sizes. The effect of an orifice was also considered. Visualization of siphon breaking and examination of transient pressure data were used to analyze siphon-breaking phenomena. Filling a horizontal main pipe at the highest point by entrained air had a large effect on triggering siphon breaking; however, the stacked air entrained during the siphon-breaking event alone was insufficient to cause the phenomenon. All of the experimental parameters were investigated by comparing the undershooting height and transient pressure data trends. Experimental investigation and observation could give the possible postulate that all experimental parameters could be described as physical parameters, such as air flow rate, water flow rate and air quantity. (C) 2012 Elsevier B.V. All rights reserved.X1179sciescopu