Fabrication, Thermophysical, and Mechanical Properties of Cermet and Cercer Fuel Composites for Nuclear Thermal Propulsion

Nuclear thermal propulsion (NTP) utilizes nuclear fission to double the efficiency of
in-space propulsion systems compared with traditional combustion rocket systems.
NTP systems are limited primarily by the fuel material choice, due to the extreme
conditions they will need to endure, including temperatures up to 3000 K, multiple
thermal cycles with rapid heating and cooling, exposure to hot flowing hydrogen,
large thermal gradients, and high neutron flux. Particle based fuels, namely ceramic-
metallic (cermet) and ceramic-ceramic (cercer) composites are both promising fuel
element material candidates for NTP. Given the high temperature nature, these
materials are difficult to fabricate and very little thermophysical and mechanical
property data exists. The fabrication of a cermet with a molybdenum-tungsten matrix
and a cercer with a zirconium carbide matrix using surrogate fuel particles have been
optimized utilizing spark plasma sintering to produce materials > 97% theoretical
density. Thermophysical properties including the coefficient of thermal expansion,
thermal conductivity, and heat capacity were determined up to 1000 °C. Compression
and notched bend bar tests up to 800 °C also provided information on the effect of
the particles to the strength of the composites. From this data, predictive models
were created to approximate the thermophysical and mechanical properties of fueled
materials for use in NTP design.

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