This report documents the efforts to model the conceptual design of the STS natural circulation flow loop using TRACE. The results, summarized in Section 2.1, support the conclusion that the conceptual STS natural circulation flow loop design provides sufficient cooling of the tungsten target and exhibits predictable flow behavior, provided that certain design features and/or operating conditions are used. In particular:
• A sufficient initial liquid volume fraction is required to avoid dryout of the target flow channels.
• Inclusion of a pressurizer or bellows volume at the top of the loop is recommended and is capable of achieving steady, non-oscillatory flow and temperature conditions at sufficiently high loop pressure.
Section 1 provides a detailed description of the geometry and assumptions used in the model, and Section 2 presents the results for the current flow loop design as well as some investigation of potential design modifications with the goal of enhancing the thermal hydraulic stability of the loop.