Experimental study of a ten sodium heat pipe bundle array with various failure modes

Alkali metal heat pipes are key components for high-temperature heat removal in microreactors, where multiple heat pipes are embedded directly within the reactor core. Their collective thermal behavior, including interactions under off-normal conditions, remains insufficiently characterized. This study investigates the performance of a ten-heat-pipe array under a range of operating conditions, including simulated failure scenarios. Under steady-state operation, the vertical configuration produced more uniform vapor temperatures among the heat pipes, albeit with slightly longer startup times and marginally higher average operating temperatures compared to the horizontal orientation. System uncertainties associated with the heat pipe array configuration were quantified to support future model validation. Complete loss-of-function conditions were simulated by replacing one or two sodium heat pipes with empty tubes. In these cases, neighboring heat pipes redistributed the thermal load, resulting in increased local heat fluxes and a corresponding rise in system temperature. This localized overloading further amplified thermal stresses on adjacent heat pipes. The experimental results provide data for characterizing thermal interactions within heat-pipe arrays, offering useful guidance for the design of future experiments and the validation of numerical models used in the analysis of heat-pipe-cooled microreactor systems.