RADIATION HEAT TRANSFER IN THE FUEL OF NUCLEAR ROCKET

Nuclear power propulsion for space applications is essential for long term high payload missions. Several nuclear reactor types were investigated between the late 1950’s and early 1970’s under the National Aeronautical and Space Administration’s (NASA) Nuclear Engine for Rocket Vehicle Application (NERVA). The NERVA reactors developed had various geometrical configurations using the same common materials and propellant, namely graphite moderated fuel elements impregnated with uranium carbide (UC) fuel particles surround by a beryllium reflector with hydrogen as the propellant. The hot hydrogen propellant flowing through the graphite core led to substantial corrosion problems and several efforts were made to protect the graphite from corrosion by the hot hydrogen propellant. Although several coating types and methods were employed only partial success was achieved. The effects of corrosion can lead to changes in heat transfer characteristics, flow changes, and reactivity degradation. This study, supported by NASA, focuses on the effects of hydrogen induced corrosion on the emissivity of the graphite fueled core. The reference data is primarily taken from the NERVA reactor identified as the Pewee Nuclear Rocket. An overview of the postmortem results of corrosion on the fuel of Pewee is described. The effects of corrosion from hydrogen exposure on graphite and the coatings used to protect the fuel elements are given. A model to calculate the effective emissivity coefficient inside a coolant channel due to varying stages of corrosion is developed. Lastly, the implementation of the effective emissivity coefficient into the radiative heat transfer equation with a brief discussion on surface area effects is provided.