A project to develop a code specifically designed to model and analyze space reactor systems is discussed. The code, named CENTAR (Code for Extended Nonlinear Transient Analysis of Extrasterrestrial Reactors), is highly vectorizable and machine-independent. Timing tests of the code have been run on VAX, Cray, NEC, Convex and SUN systems. It has been found that CENTAR executes approximately seven times faster in vector mode than scalar mode on a Cray X-MP. A one-loop model of a thermoelectric-based space reactor system (SP-100-like) was developed to demonstrate the code's capabilities. The model consisted of 24 components containing a total of 67 computational cells. Using a constant time step, this model ran two times faster than real time on a Cray X-MP. A code assessment plan is currently under development.