Toshiki Ezure

Experimental Study on Gas Entrainment at Free Surface in Reactor Vessel of a Compact Sodium-Cooled Fast Reactor

An innovative sodium-cooled fast reactor has been investigated as part of the fast reactor cycle technology development (FaCT) project. In the reactor, a compact reactor vessel (R/V) with increased sodium flow velocity was designedto reduce the construction cost. One of the thermal hydraulic problems associated with this design is gas entrainment at the free surface in the R/V. Horizontal plates are set below the free surface in order to prevent the gas entrainment. A water experiment was performed using a partial model built to 1/1.8 scale. The objective was to investigate the occurrence of gas entrainment under certain conditions and the mechanism of the gas entrainment. It was found that there were two types of gas entrainment phenomenon, and the conditions for their occurrence were far different from the rated condition in the reactor. One type of gas entrainment occurred at the wake region of flow around the cold leg pipe created due to the larger horizontal velocity in the R/V. The other type of gas entrainment occurred at the region between the hot leg pipe and the R/V wall when the coolant level was low and the downward velocity was large. The mechanisms of the gas entrainment at the two regions were clarified by the detailed measurement of transient flow velocity field.

Transient Behavior of Gas Entrainment Caused by Surface Vortex

A compact sodium-cooled reactor is an important candidate as a fast breeder reactor (FBR) and has been investigated in the feasibility study of FBR cycle. Due to the compact sizing of the reactor vessel, gas entrainment at the free surface of sodium coolant becomes one of the significant issues for reactor design, and it is required to clarify the criterion of gas entrainment at free surface and the tolerance. In the present study, some visualization experiments were performed in a water-air system focusing on the gas entrainment due to surface vortex and its transient phenomena. Influences of horizontal velocity were clarified by the visualization. The gas entrainment due to the surface vortex occurs intermittently. Time trends of circulation and length of gas core for the intermittent surface vortices were measured by the particle image velocimetry and visualization. It was found that the gas core length extends with time delay to the increase of circulation around the vortex.

Experimental Study on Gas Entrainment Due to Nonstationary Vortex in a Sodium Cooled Fast Reactor—Comparison of Onset Conditions Between Sodium and Water

An innovative sodium cooled fast reactor has been investigated as part of the fast reactor cycle technology development project. In the reactor, a compact reactor vessel (R/V) with increased sodium flow velocity was designed to reduce the construction cost. One of the thermal hydraulic problems in this design is gas entrainment at the free surface in the R/V. In most of past studies, water experiments were performed to investigate the gas entrainment in the reactor. It is necessary to evaluate an influence of fluid physical property on the gas entrainment phenomena. In this study, sodium experiments were carried out to clarify the onset criteria of the gas entrainment due to a free surface vortex. Water experiments using a test section in which geometry is the same as that in the sodium tests were also performed. The gas entrainment in water slightly tended to take place in comparison with that in sodium under low velocity conditions. Overall, the onset condition map on the lateral and downward flow velocities in the sodium and water experiments were in good agreement.

Experimental Study on Gas Entrainment Due to Non-Stationary Vortex in a Sodium Cooled Fast Reactor: Comparison of Onset Conditions Between Sodium and Water

An innovative sodium cooled fast reactor has been investigated as part of the fast reactor cycle technology development (FaCT) project. In the reactor, a compact reactor vessel (R/V) with increased sodium flow velocity was designed to reduce the construction cost. One of the thermal hydraulic problems in this design is gas entrainment at the free surface in the R/V. In most of past studies, water experiments were performed to investigate the gas entrainment in the reactor. It is necessary to evaluate an influence of fluid physical property on the gas entrainment phenomena. In this study, sodium experiments were carried out to clarify the onset criteria of the gas entrainment due to a free surface vortex. Water experiments using a test section in which geometry is the same as that in the sodium tests were also performed. The gas entrainment in water slightly tended to take place in comparison with that in sodium under low velocity conditions. Overall onset condition map on lateral and downward flow velocities in the sodium and water experiments were in good agreement.Copyright