Brian E. Williams

A TRICARBIDE FOAM FUEL MATRIX FOR NUCLEAR THERMAL PROPULSION

A team from Ultramet Inc., Sandia National Laboratories and the University of Florida has been developing a new high temperature, tricarbide fuel matrix consisting of ZrC, NbC and UC using an open-cell reticulated foam skeleton. The new fuel matrix is the product of a NASA STTR project funded through Marshall Space Flight Center. The new fuel is envisioned for use in nuclear thermal propulsion systems, bi-modal reactors and terrestrial high temperature gas reactors and builds on the tricarbide fuel research in the former Soviet Union. The new fuel is mechanically robust and very efficient given its extremely high surface area, higher melting point, minimal thermal stresses, and much reduced pressure drop compared to conventional fuel types. The matrix is anticipated to operate at temperatures as high as 3000 K with minimal hydrogen erosion. The foam is an engineered material in which the porosity, size and thermal conductivity of the ligaments can be controlled independently to meet specific requirements. In this article, we review the vapor phase alloying of the tricarbide to produce a homogeneous solid mixture of the constituents using TaC as a UC surrogate with the option of additional diffusion barrier layers as required. A credible reactor design and results of a new MP-CFD modeling capability using detailed simulation of the porous media are presented along with new FEM CFD simulations of a complete fuel element and core assembly. A new CVI reactor for the deposition of the tricarbide containing UC is now operational at the University of Florida. This article presents our recent experiences with UC depositions and results from hot hydrogen testing of these materials at 3000 K.