Deposition of cesium iodide particles in bends and sections of vertical pipe under severe accident conditions

A relatively small-scale aerosol deposition experiment (called WAVE) in a q uartz glass pipe with a 90 degrees bend followed by a short straight sectio n was performed at Japan Atomic Energy Research Institute to investigate th e effect of pipe orientation on the cesium iodide (CsI) aerosol deposition. In these basic configurations, the section after the bend was either horiz ontal, upward and downward, respectively. The upward case showed 5 and 10 t imes larger CsI mass deposition in the vertical section of pipe than the ho rizontal and downward configurations, respectively. The experiments were an alyzed by coupling a three-dimensional fluid-dynamic and an aerosol behavio r codes. The calculations were in reasonable agreement with the measured ae rosol mass deposition except for the upward case because the principal CsI deposition mechanism is thermophoresis which depends on the thermal gradien t in gas and the gradient was well predicted by the fluid-dynamic code. In order to better predict the deposited mass in vertical section of upward ca se, Nusselt number which is used for thermophoretic deposition calculation had to be reevaluated carefully by considering the effect of secondary free convection in the vertical pipe which flowed opposite to the main stream. (C) 2000 Elsevier Science Ltd. All rights reserved.