Coupled multi-physics analysis of low-enriched uranium nuclear thermal propulsion reactors

Abstract

The growing demand for high-performance propulsion systems in aerospace has highlighted that current multi-physics coupling technologies cannot accurately assess the performance and safety of low-enriched uranium nuclear thermal propulsion reactors (LEU-NTPRs) under extreme conditions. Accordingly, this study employs advanced multi-physics coupling methods to investigate the performance, safety, and thermoelastic behavior of LEU-NTPR assemblies and their core geometries under several extreme boundary conditions, providing a scientific basis for reactor design. By utilizing OpenFOAM, a multi-region neutron transport-conjugate heat transfer coupling solver is developed to perform pin-by-pin multi-physics coupling calculations for reactor assemblies and full-core geometries. Both the neutron transport and conjugate heat transfer equations are solved, and the resulting steady-state temperature distribution is used as the input for thermoelastic calculations. Thermoelastic analyses are conducted using the solid4Foam solver of OpenFOAM by assuming a small strain to evaluate the displacement and equivalent thermal stress distributions. The assembly coupled simulation shows a significantly improved prediction accuracy for fuel temperature compared to non-coupled methods. Core-coupled simulations confirm that the conceptual design adheres to physical and thermal engineering standards. A thermoelastic analysis reveals that the maximum thermal stress is ∼ 246 MPa, while the maximum fuel displacement reaches 7.1 mm. These findings suggest that thermal stress, particularly in regions with significant temperature gradients, can be a critical factor limiting core power output. By adjusting the core inlet flow rates, the maximum assembly temperature is controlled within safe limits while achieving uniform coolant outlet temperatures. The proposed multi-regional coupling approach enhances the prediction accuracy for the performance, safety, and thermoelastic characteristics of LEU-NTPRs under extreme conditions, while ensuring a high specific impulse in propulsion systems.