Experimental design for transient in-pile boiling studies at the TREAT facility

Transient irradiation testing for nuclear fuels and materials requires unique facilities that can provide necessary neutronic and thermal hydraulic boundary conditions. Especially in water reactors, limiting material performance is frequently closely related to limiting conditions such as critical heat flux and post-departure from nucleate boiling conditions. Out-of-pile experiments provide crucial data for understanding these behaviors though the addition of irradiation effects is known to fundamentally change performance behavior. Extensive experimental capabilities and experiments are under development to support testing at the Transient Reactor Test (TREAT) facility. Several test vehicles are rapidly reaching readiness to support testing of Accident Tolerant Fuels and other advanced light water reactor fuels needs. Specific design targets include detailed characterization of boiling behavior during transient irradiation events with cladding-surface temperature measurement using thermocouple attachment designs and infrared thermometry and void fraction using electrical impedance based techniques. This paper summarizes experimental capabilities and early results to support thermal hydraulic characterization under irradiation. It also provides an introduction to thermal hydraulic experiments planned to characterize transient in-pile boiling behavior associated with critical heat flux under fast transient conditions.