Progress on the University of Wisconsin SCW heat transfer tests

Full text of publication follows: As advancements in materials are being generated, there is increasing interest to operate nuclear reactors at higher temperatures to increase the plant efficiency and lower electricity production costs. A particularly interesting way to increase the efficiency by as much as 30% above that of current light water reactors is to operate the nuclear reactor with supercritical water (SCW) as the coolant. The Generation IV initiative has included SCW reactors as one of the viable candidates to be considered for further development and possible deployment. Associated with this reactor concept are several areas of fundamental research that require further study. Supercritical water is a unique fluid that experiences dramatic changes in its thermo-physical properties near the pseudo-critical point. These changes can substantially alter local heat transfer characteristics. Existing models and correlations, such as the Dittus-Boelter heat transfer correlation, are therefore not valid for these conditions. A survey of existing work on SCW heat transfer shows that the existing models and correlations predict widely varying results and depending on which models are used may make detailed reactor core designs unfeasible. This paper focuses on the progress of modification of the University of Wisconsin's SCW loop to investigate heat transfer on simulated fuel rods capable of heat fluxes up to 1500 kW/m2. A summary of the progress on measuring the flow velocity through a sapphire window using both LDV and PIV techniques will be discussed along with preliminary heat transfer data from the loop. The SCW loop is designed to operate at temperatures of 550 C and flow rates of 80 gpm, resulting in velocities passed a single 1.03 cm fuel pin of 1-8 m/s consistent with the velocities anticipated in the INEEL SCWR design. (authors)