Taizo Kanai

Experimental Study on Wave Propagation Behavior on Free Surface of Lithium Flow for IFMIF

Velocity measurement of surface waves on high-speed liquid lithium (Li) flow was conducted by using the Li circulation loop at Osaka University to support target monitor and diagnostics applications for the International Fusion Materials Irradiation Facility (IFMIF). Free surface shapes were recorded with a high-speed video camera, and surface waves were tracked with the statistical correlations of image intensity patterns over a velocity range of 5 to 15 m/s. As a result, the velocity distribution of surface waves was measured. The development of surface velocity beyond the nozzle edge was clearly measured. The velocity measurement by this method might suffer from some influence from stationary waves, which were generated by a damaged nozzle edge. The measured velocity in a region free from stationary waves was seen to exceed the mean flow velocity, probably due to two-dimensional regular waves. For this case, the measured velocity may consist of the advection velocity of the Li flow and the phase velocity of the wave. For an irregular wave region, the measured velocity was shown to be approximately the same as the mean flow velocity. The present flow velocity measurement can be used in the high-velocity range where random waves are generated.

Effect of Two-Phase Flow Structure in Decontamination Factor of Filtered Containment Venting System

In order to gain the best use of filtered containment venting systems (FCVSs), the decomtamination factor of FCVSs is to be investigated as a function of system parameter including steam flow rate, pressure, temperature, water level, and operating time. A full-height test facilities were designed and constructed in Central Research Institute of Electric Power Industry (CRIEPI), Japan to evaluate the decontamination factor (DF) in FCVSs. The target types are the orifice and the venturi FCVSs. The height and the internal diameter of the cylindrical test vessel is 8 m and 0.5 m. Bubbly flows were visualized through the view window up to 0.8 MPa and 170 °C. Steam bubbles in 0.2 wt% sodium thiosulfate and 0.5 wt% sodium hydroxide were found to be much smaller than those in water. The DF were evaluated for the aerosol, elemental iodine and organic iodine. The installed aerosol optical spectrometer measures the number density and the diameter of aerosols. The concentrations of elemental iodine were quantified with an inductively-coupled plasma with mass spectrometry (ICP-MS). The concentration of organic iodine was quantified with a gas chromatography with mass spectrometry (GC-MS). In order to investigate two-phase flow dynamics in the vessel, separate effect tests were conducted with air-water test facility. The height of cylindrical test vessel is 8 m. Visual observation was conducted for two internal diameter levels: 0.05 and 0.5 m. High speed video frames were recorded through the transparent (acrylic) vessel wall. Wire-Mesh Sensors (WMS) were installed to acquire a cross-sectional void fraction to compare with DF in the facility. On the basis of the obtained database, we develop the FCVSs performance evaluation technique and propose an optimal FCVSs operation method for a further safety improvements of the nuclear power plant.© 2014 ASME

Development of a Multi-Dimensional Measurement Sensor of Void Fraction and Phasic Velocity for Boiling Two-Phase Flow in a 5×5 Heated Rod Bundle

A subchannel void sensor (SCVS) was developed to measure the cross-sectional distribution of a void fraction in a 5×5 heated rod bundle with o.d. 10 mm and heated length 2000 mm, and applied in a boiling two-phase flow experiment under the atmospheric conditions assumed in an accident and spent fuel pool. The SCVS comprises 6-wire by 6-wire and 5-rod by 5-rod electrodes. Wire electrodes 0.2 mm in diameter are arranged in latticed patterns between the rod bundle, while a conductance value in a region near one wire and another gives a local void fraction in the central-subchannel region. 32 points (= 6×6−4) of the local void fraction can be obtained as a cross-sectional distribution. In addition, a local void fraction near the rod surface can be estimated by a conductance value in a region near one wire and one rod using the simulated fuel rods as rod electrodes, which allows 100 additional points (=4×25) of the local void fraction to be acquired. The devised sensors are installed at five height levels to acquire two-phase flow dynamics in an axial direction. A pair of SCVS is mounted at each level and placed 30 mm apart to estimate the one-dimensional phasic velocity distribution based on the cross-correlation analysis of both layers. The time resolution of void measurement exceeds 800 frames (cross-sections) per second. The heated rod bundle has an axially and radially uniform power profile, and eight pairs of sheath thermocouples are embedded on the heated rod to monitor its surface temperature distribution. The boiling two-phase flow experiment, which simulated a boil-off process, was conducted with the devised SCVS and experimental data was acquired under various experimental conditions, such as inlet-flow velocity, rod-bundle power and inlet subcooling. The experimental results exhibited axial and radial distribution of two-phase flow structures, i.e. void-fraction and phasic-velocity distributions quantitatively.Copyright