[en] A computer program which simulates MUTR operation over a wide dynamic operating range has been designed and tested. This simulator is part of a larger effort on reactor dynamics and control to be undertaken by the reactor facility staff. The simulator model is divided into four interactive modules: (1) Reactor Kinetics, (2) Fuel Temperature, (3) In-Core Water Temperature, and (4) Bulk Water Temperature. A lumped parameter model is assumed within each module. Control of the simulator (as well as the reactor) is affected by several different means: (1) control rod position, (2) source in/out, (3) primary pump on/off, (4) HX1,2 on/off, and (5) diffuser pump on/off. Pertinent measurable parameters which may be compared to simulator output are (1) power level, (2) fuel temperature, and (3) bulk water temperature. The essence of the lumped parameter simulator model is a system of coupled, first order non-linear, stiff differential equations. Six delayed neutron groups have been used in the kinetics module, as well as the prompt jump approximation to reduce the dynamic range of the time constants. The system of differential equations was cast into finite difference form using a semi-implicit iterative scheme which is able to accommodate stiff equations since the spectrum of system time constants runs from about 0.1 second to hours. Preliminary simulator results indicate general agreement with reactor data after some adjustment of equation coefficients such as heat transfer coefficients, and reactivity coefficients. Work is continuing on improving the model. (author)