Hydrodynamic instabilities in flat-plate-type fuel assemblies Original Research Article

Flow-induced static and dynamic instabilities observed in the cores of many research and power reactor designs are investigated using a system of stacked thin flat rectangular fuel plates. In the engineering test reactor (ETR) the core consists of up to 19 thin flat rectangular fuel plates stacked in parallel. The plates are separated by narrow channels through which the coolant flows. In experimental setups the fuel plates have been observed to plastically collapse or become dynamically unstable at high coolant flow rates. In this paper, analytical models of systems of thin flat rectangular fuel element plates are developed which take into account the effects of the fluid reactive loadings, coolant flow velocity, plate aspect ratio and the channel height between the plates. Instability criteria, based on divergence and dynamic resonance, for design against flow-induced instabilities in flat plate-type reactor cores are presented. These results are compared with experimental observations from previous pre-reactor and assembly mock-up tests, and the Miller critical flow velocity theory.