Wall Effects on Terminal Velocity of Test Fuel Bundle in the Fuel Test Loop of High Flux Research Reactor

Fuel Test Loop (FTL) is a self-contained independent experimental loop which is designed for testing of nuclear fuel materials under simulated power reactor conditions in the High Flux Research Reactor being developed at BARC. It is a high-pressure loop with maximum operating pressure up to 17.5 MPa and maximum operating temperature up to 330 °C. The In-Pool Test Section of the FTL consists of a series of concentric tubes with different thicknesses and functionality. The test fuel bundle resides within the innermost Fuel Tube which is further enclosed within an internally insulated Pressure Tube which acts as a pressure boundary enclosure to the test fuel bundles. The present work deals with the investigation of wall effects on the terminal velocity of test fuel bundles falling under gravity within the In-Pool Test Section. While loading/unloading of the test fuel bundle, accidentally the fuel bundle may fall under the influence of gravity within the fluid filled Fuel Tube. The minimum gap between the fuel bundle and the fuel tube is 2 mm. Thus, the wall effects on the velocity of the falling fuel cannot be neglected. The purpose of the present work is to estimate this wall effects on the terminal velocity of the falling fuel in terms of Drag Coefficient. This involves, initially estimating drag characteristics and terminal velocities with wall effects for different geometries, and finally predicting the overall characteristics with the test fuel bundle as the geometry of interest. To fulfill this objective, an analytical methodology is established which has been validated through a commercial code.