Mechanistic modeling for ring-type BWR fuel spacer design 1. Drift flow model

The fuel spacer is one of the components of a fuel rod bundle and its role is to maintain an appropriate rod-to-rod clearance. Since the fuel spacer i nfluences liquid film flow on fuel rods in BWR core, its specification has a strong effect on thermal hydraulics in the core such as critical power an d pressure drop. Spacers have been developed through empirical modification s, so that a large amount of test data are required far optimum design of t he spacer. It is, therefore, important to develop a mechanistic model of th e spacer for future design of BWR fuel bundles. The authors considered that enhancement of droplet deposition is induced downstream of the spacer wher e velocity profiles split by a spacer are recovered into one velocity profi le; higher velocity in the core and lower velocity in a gap clearance betwe en the rod surface and the spacer. In this paper, the effect of spacer geom etry on the droplet deposition rates downstream of it was investigated expe rimentally in a open rectangular channel using air and water as test fluids . A Phase Doppler Anemometer (PDA) was used for this measurement. In additi on, velocity profile equations were obtained from the drift flow model. Fro m these results, a mechanistic model of enhancing droplet deposition rate d ownstream of the spacer was proposed. (C) 2000 Elsevier Science S.A. All ri ghts reserved.