As part of the Global Threat Reduction Initiative (GTRI)the High Flux Isotope Reactor (HFIR) is converting itsfuel from high-enriched uranium to low-enriched uranium.Currently, multi-physics simulations that model fluid-structureinteraction (FSI) phenomena are being performed to ensure thesafety of the reactor with the new fuel type. A monolithicsolver that fully couples fluid and structural dynamics is usedto model deflections in the new design. A classical experimentis chosen to validate the capabilities of the current solver andthe method. A single plate simulation with various boundaryconditions as well as a 5-plate simulation are presented. Useof the monolithic solver provides stable solutions for the largedeflections and the tight coupling of the fluid and structure and the maximum deflections are captured accurately.