An experimental investigation of the fluid structure interactions of a single curved nuclear fuel plate in a narrow channel

Abstract

Nuclear research reactors are major scientific tools used by researchers all over the word to produce medical isotopes, irradiated materials, as well as study nuclear processes. Most fuel for research reactors is in the form of plates of uranium clad in aluminum. Forced water flows across the plates for cooling and reaction moderation. The Global Threat Reduction Initiative (GTRI) is an international effort to develop an acceptable low enriched uranium(LEU) fuel to replace the current high enriched uranium (HEU) fuel in research reactors. Because HEU fuel could be used for nuclear weapons, the goal of the GTRI is to prevent proliferation of HEU. The fuel plates and their assemblies must be redesigned using LEU fuel. Also, the LEU assemblies must fit the same profile within the reactors as the HEU assemblies and must provide a similar neutron distribution. The redesigned fuel plates will be thinner and the inter-plate coolant channels will be wider. The fluid structure interaction (FSI) between the fuel plates and coolant needs to be investigated to understand the potential for channel collapse. Channel collapse occurs when plates deflect to the point of touching the neighboring plate significantly cutting off coolant supply. Fluid structure interaction experiments were carried out to validate numerical FSI models that will be used to design structurally stable LEU fuel plates and assemblies. Past analysis has been conducted on flat and involute plates in single and multiple plate assemblies with channels of equal thickness. No previous experiments have been carried out on a curved plate with unequal channel gaps. The experimental setup consists of two stainless steel cylinders with a plate of 0.4604 mm thickness between them to form two flow channels. The inner channel is designed at 2.032 mm thickness and the outer channel thickness is 2.54 mm. The unequal channels are intended to simulate the maximum and minimum allowable channel thickness in the fuel assembly tolerances for the University of Missouri Research Reactor. The test plate is much thinner than the prototype fuel plate design in order to provide measurable deflections for the flow rates that are achievable in the current flow loop. Deflection is measured through plexiglass windows in the outer cylinder using a laser displacement sensor. The flow experiments showed that curved plates deflect into the initially larger channel and have a maximum deflection that increases at a rate greater than linearly with mass flow of the water. The maximum deflection measured was roughly 0.25 mm at a mass flow rate of 2.5 kg/s (average channel velocity of 4.4 m/s). When deflection is plotted against flow rate, a hysteresis is seen between subsequent sets of measurements throughout the experiment. The hysteresis was investigated and attributed to thermal expansion of the test plate due to the pump heating the circulating water. The experimental pressure results matched well with the numerical FSI models of the experimental setup.