Thermal-hydraulic response of the TREAT multi-vessel static environment test vehicle

As part of the resumption of transient testing in the United States, multiple test vehicles are currently under design, which are ideally suited for achieving various test environments. Of these, the multistatic environment rodlet transient test apparatus (SERTTA) is the most mature design. The test vehicle is designed for testing up to four isolated specimens under a variety of conditions ranging from gas, steam, water, and liquid sodium. During proposed transient events such as reactivity initiated accidents (RIA) and loss of coolant accidents (LOCA) in reactors, prototypic environments dictate a wide range of thermal-hydraulic boundary conditions. The purpose of the this work is to provide the thermal hydraulic response of the Multi-SERTTA test vehicle subjected to fuel specimen energy depositions representative of pressurized water reactor (PWR) conditions. Calculations are performed for a RIA-type power pulse in a 10 cm long UO2-zircaloy rodlet immersed in a water environment in Multi-SERTTA. The relatively small volume available in the Multi-SERTTA causes the vessel pressure to be very sensitive to total energy deposition. The effects of total energy deposition and free gas volume in the pressure vessel are presented. The design provides additional flexibility of environment conditions through use of the expansion tank volume. The results show the influence of the vehicle geometric and safety constraints and provide indication of the expected thermal-hydraulic conditions relative to typical RIA transient events.