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This technical note deals with simulation-based design optimization for the ex-core Transformational Challenge Reactor (TCR). Three-dimensional geometry was created for the TCR ex-core. Computational fluid dynamics (CFD) simulations were performed to optimize forced circulation airflow. The CFD model includes thermofluidic phenomena such as convective, conductive, and radiative heat transfer. The simulation results are presented for three different inlet coolant mass flow rates (2, 4, and 8 kg/s). The observed optimized flow rate for the base configuration was 5 kg/s. The calculated peak temperatures were within the safety limits for all components including the bio-shield (433 K) and the shroud mechanism (473 K). [ABSTRACT FROM AUTHOR]

To enable the design of a light water small modular reactor, the boiling flow inside a helical coil steam generator has been simulated with the two-fluid model in Nek-2P. Nek-2P is the multiphase branch of the spectral element code Nek5000. Details of the implementation of the two-fluid model and the included closure models are discussed. The presented closure models include interactions for momentum, heat, and mass transfer between phases. Models for the drag, lift, and turbulent dispersion forces are included. The complete model is fully consistent in the limits of both phasic volume fractions approaching zero and is able to simulate flows of dispersed vapor, continuous liquid, dispersed liquid, continuous vapor, or any combination thereof. The closure models and their implementation in Nek-2P have been validated by comparing to experimental data for a boiling flow, demonstrating excellent agreement. Results from the simulation of the helical coil indicate strong phasic separation driven by the effects of buoyancy and inertia. Significant differences were observed in the results compared to simulations performed using Star-CCM+, although these differences were somewhat expected. [ABSTRACT FROM AUTHOR]