Design and Heat Transfer Analysis of Spherical Cermet Fuel for Nuclear Thermal Propulsion Based on Tungsten Coated Particles

Abstract

Nuclear thermal propulsion (NTP) is suitable for future manned Mars missions and beyond due to its high power and high specific impulse. Considering the low development level of ZrC fuel balls and the complex preparation process of prismatic cermet, this paper proposes a new type of NTP fuel: spherical cermet fuel pellet, which has the advantages of high development level of cermet materials and can be prepared integrally through 3D printing. Based on existing test results and heat transfer analysis, the fuel is designed in materials and geometric dimensions. During the design process, it is find that the size effect of coated particles will form local hot spots due to the difference of thermal conductivity between UO2 and tungsten matrix. Formulas for the temperature and the local hot spot in cermet fuel ball are derived. These formulas reveal the relationship between the peak temperature and the design parameters. According to the requirements for temperature, heat transfer area, and uranium loading, the fuel is designed in detail to maximize its applicable hydrogen temperature. The final design is that the cermet fuel ball has a diameter of 5.6 mm with cladding thickness 300 μm, using pure tungsten as the matrix and cladding, and is filled with 53 vol% tungsten coated particles. The coated particle diameter is 220 μm with coating thickness 10 μm. Analysis of the applicable hydrogen temperature for this fuel shows that it can satisfy a hydrogen temperature of 2600∼2850 K for NTP pebble bed reactor of 1000∼2000 MW. This research designs a new type of NTP fuel and provides a basis for core neutronics and thermohydraulic analysis with spherical cermet fuel pellet.

Keywords: nuclear thermal propulsion, CERMET fuel, heat transfer, Hot spot, Hydrogen temperature