High-resolution thermal analysis of nuclear thermal propulsion fuel element using OpenFOAM

Highlights: • NTP provides high thrust and specific impulse for space exploration. • Various LEU NTP concepts are typically analyzed using reduced-order tools. • Reduced-order engineering tools rely on empirical heat transfer correlations. • High order numerical CFD tools (e.g. OpenFOAM) can improve the computational fidelity. • High resolution analysis of a fuel element was validated against experimental data. This paper conducts high-resolution thermal hydraulic analysis of a Nuclear Thermal Propulsion (NTP) Fuel Element (FE) using a finite volume approach. Recent NTP design efforts have focused on using low-enriched uranium (LEU) fuel as an alternative to the historical highly-enriched uranium (HEU) fuel. In addition to changing materials' properties, variations in dimensions and flow characteristics are also considered. This makes the applicability of legacy experimental data questionable for the new LEU designs, as the data was generated for a specific range of design characteristics. Nowadays, there is limited accessibility to experimental capability under realistic hot hydrogen conditions. However, some experimental setups could be replaced or complemented by higher-order numerical analysis, which is the end objective of the computational framework developed here. This study implements a 3D conjugate heat transfer (CHT) numerical solver between solid and fluid regions using OpenFOAM Computational Fluid Dynamic (CFD) toolbox. The hydrogen flow in the fluid region is simulated using Reynolds-averaged Naiver-Stokes (RANS) model, while the solid region is modeled using a conduction heat transfer solver. The 3D simulation results are validated against experimental data obtained from the Nuclear Engine for Rocket Vehicle Application (NERVA) Nuclear Rocket Experimental (NRX) A6 program. The latter shares similar design parameters with modern NTP systems, such as dimensions and flow conditions. In addition, legacy heat transfer correlations were implanted in a reduced-order 1.5D semi-analytic solution, and the results were compared against the OpenFOAM solution. The results presented in this paper conclude that OpenFOAM can serve as a high-resolution thermal hydraulic code both for reproducing legacy experiments and educating reduced-order models.