Hiroyuki Miyakoshi

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.

Study on Mixing Due to Transversal Flow in a Fuel Subassembly of Fast Reactor: Sodium Experiment Using a 37-Pin Subassembly Model

Estimation of the highest temperature in a fuel subassembly is needed for safety and reliable operation of fast reactors. Cross flow has a significant role for mixing phenomena in the subassembly. Especially, the cross flow will be enhanced in a deformed pin bundle of high burnup core. Such mixing due to the cross flow was investigated. Sodium experiments were carried out using a wire wrapped 37-pin subassembly model. In order to see a cross flow in a simple and clear geometry as an element of mixing phenomena, a blockage was installed in the subassembly. Mixing due to the cross flow was found in the experiment. The subchannel analysis code, ASFRE, was applied to the experimental analyses. Measured axial and transverse temperature distributions in the subassembly were correlated with the cross flow and the wire spacer. The calculated temperature profiles were in good agreement with the experimental results. ASFRE simulated the influence of the wire spacer also. Database for the mixing phenomena with the cross flow was obtained.Copyright