Issues in the Closed-Loop Digital Control of Reactor Power: The MIT Experience

The 5 MWt MIT Research Reactor´s license was recently amended to permit the general use of a closedloop digital control system for the adjustment of reactor power. This regulatory approval is significant because the avoidance of challenges to the reactor´s safety system now depends on the design of the controller rather than, as was previously the case, on the characteristics of the actuator. Considerations involved in the granting of this license amendment are discussed including information on the technical basis for the controller, the prevention of challenges to the safety system, and the relation between the control and safety systems. The results of the initial use of the controller are presented together with a discussion of the possible applications of this controller.