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.