Assessment of fission fragments enhancement for nuclear thermal propulsion

Abstract

A novel concept of Nuclear Thermal Rocket (NTR) propulsion is presented. It is based onthe direct conversion of the kinetic energy of the Fission Fragments (FFs) into the propellantenthalpy. The FFs can escape from an extremely thin layer of fissionable material: a sufficiently large surface coated with few micrometers of Americium 242m, confined by a neutron diffuser, may become a critical reactor. The novel FF NTR propulsion concept may allow the propellant to achieve temperatures higher than the nuclear fuel, thus overcoming the limit in the specific enthalpy achievable by the propellant in the conventional solid-core NTR propulsion. Such a limit comes from the need to keep the temperature of the fuel material within a safe interval by using conventional convective heat transfer mechanism. A preliminary assessment of the FF NTR concept’s propulsion characteristics has been carried out using an in-house developed software system which integrates a Computational Fluid Dynamic code, a neutronic code and a Monte Carlo code. The assessment shows the potential to reach specific impulses of about 15,000 m/s and thrust levels in the range 4,000 to 6,000 N, with a trhust to weight ratio of a few percent of the acceleration of gravity. Such performances may make the FF propulsion a candidate for human missions to the planet Mars.