A training simulator that duplicates a Savannah River Plant (SRP) reactor control room is currently under construction. Because of the complexity of the SRP reactor control and instrumentation systems, a multinode neutronics model is necesssary in order to simulate the reactor core behavior. A 240-node core model, using a semi-implicit (SI) solution technique, has been developed to fill that need. The SI model has been tested with a range of transients and is found to provide an accurate simulation with the potential of running significantly faster than real time on the reactor simulator minicomputer complex.