Development of a new test section for the experimental analysis of critical velocity in flat plate fuel element for nuclear research reactor

Abstract

The fuel elements of a MTR type nuclear reactor are mostly composed of aluminum containing the core of uranium sílica (U3Si2) dispersed in an aluminum matrix. These plates have a thickness of the order of millimeters and are much longer in relation to their thickness. This configuration, combined with the need for a flow at high flow rates to ensure the cooling of the fuel element in operation, may create problems of mechanical failure of fuel plate. In the case of critical velocity, excessive permanent deflections of the plates can cause blockage of the flow channel in the reactor core and lead to overheating in the plates. In the first work a test section that simulates a plate-like fuel element with three cooling channels was developed. The dimensions of the test section were based on the dimensions of the Fuel Element of the Brazilian Multipurpose Reactor (RMB). The critical velocity was reached with 14.5 m/s leading to the consequent plastic deformation of the flow channel plates. The signals of extensometers from the test section also showed excitation frequencies due to fluid related phenomena, for example: pressure pulse due to cavitations, fluid resonances, etc. The new test section is being designed to allow internal instrumentation and visualization for a better understanding of the fluid structure coupling. With this new section of test we intend to generate data that allow the assembly of a model that can better simulate the phenomenon of critical velocity for the RMB.