The nuclear thermal propulsion (NTP) system can shorten the travel time in deep space exploration and reduce the initial mass of the launch vehicle due to its superior characteristics including high specific impulse and large thrust. Particle bed reactor (PBR) is the most appropriate one among all reactor concepts to equip the NTP systems. By employing small fuel particles and radial flow path of coolant in the heat release region, PBR can achieve high power density and small core pressure drop. To make the best use of PBR, the thermal-hydraulic design of the fuel element should be carefully considered and a flow-power matching technology should be developed.The fuel element consists of the hot and cold frits used to contain the nuclear particle fuel and control radial flow of hydrogen over the particle bed. Usually, a cold frit dominated design is adopted to relieve the unbalanced axial pressure difference between the inlet annulus and hot gas channel in the fuel element and improve the robustness of flow distribution. However, this measure could lead to a significant pressure drop in the PBR core. In this paper, a novel design employing a divergent hot gas channel is proposed to achieve a uniform flow distribution without any additional flow resistance. Through the one-dimensional pressure variation analysis in the inlet annulus, hot gas channel, cold frit, hot frit, and fuel particle bed, the governing equation of dimensionless axial velocity in the inlet annulus is established. Based on this, the model to determine the cross-section of the hot gas channel is derived and the geometry parameters of this fuel element with a conical angle in the hot gas channel are obtained.Afterward, the flow and heat transfer process in this fuel element is simulated by using computational fluid dynamics (CFD) code, and the indicated effective reduction of flow mal-distribution verifies the theoretical model.This study shows that the proposed design of the divergent hot gas channel can provide a new idea for thermal-hydraulic optimization of the fuel element and particle bed reactor.

Preliminary Design of a Fuel Element With Divergent Hot Gas Channel In Particle Bed Reactor for Nuclear Thermal Propulsion

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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