Instability measurement for plate-type fuels subjected to narrow-parallel flow

Abstract

Plate-type fuel assemblies are utilized in many research reactors. Some are open-loop, pool-type reactors, but others are pressurized reactors with high coolant flow rates. Parallel flows between the fuel plates can make these plates unstable. Several studies in the early 60s reported that the plates could lose their stability through a static type of instability. In accordance with studies in the 70s, however, the type of instability, whether static or dynamic, may depend on the boundary conditions. In this study, we present experimental observations of the instability of a fuel plate subjected to a narrow-axial flow between several different fuel plates. We sought to measure and compare the critical flow velocity with predictions according to Miller’s theory, which is generally used during the design of a plate-type fuel. For this experiment, we installed strain gages on a target plate (instrumented plate) positioned at the center of five simulated plates to reflect the fluid interaction in the narrow gaps between the plates. Pressure sensors were also installed to measure the static pressure differences between two channels adjacent to the target plate in an effort to identify the moment of instability. We observed that the stability of the target plate is lost due to a static type of instability at a flow velocity of 16.4 m/s, slightly lower than the flow velocity predicted using Miller’s equation for a fixed–fixed boundary condition.