Patent Number: 051125650
Section: summary

TECHNICAL FIELD The present invention relates, in general, to a control technique for a nuclear reactor and, more particularly, to a control technique for changing the reactivity of the nuclear reactor by incrementally changing a control parameter by a fixed amount. BACKGROUND ART Control systems for nuclear reactors have been known for a number of years and have been improved significantly through the use of digital computers. Such computers receive information from the nuclear reactor through sensors and signal conditioners and by applying a series of mathematical manipulations, known as the control algorithm, produce output signals which are applied to actuating systems or control devices that modify the reactivity of the nuclear reactor. Many different algorithms have been developed for the purpose of digital control and the output signals produced thereby typically consist of a combination of digital signals which cause the actuating or control device to move at some combination of acceleration, velocity and/or position to vary the reactivity of the reactor. It has been found that the resulting algorithms are typically very complex in nature, and require substantial computer time and power to implement. Because of the foregoing, it has become desirable to develop a simple control technique (algorithm) which can incrementally change a parameter, such as the position of an actuator, by a fixed unit to incrementally change the reactivity of the nuclear reactor. SUMMARY OF THE INVENTION The present invention solves the problems associated with the prior art and other problems by providing a control technique (algorithm) for incrementally changing a control parameter by a fixed unit to change the reactivity of the nuclear reactor. The control technique utilizes three states: (1) reactivity increased as a result of one unit of motion of a movable control; (2) no change in the movable control resulting in no change in reactivity; or (3) reactivity decreased as a result of one unit of motion of the movable control. The algorithm has a very short cycle time compared with delayed neutron lifetimes in the reactor permitting almost instantaneous correction of errors. In addition, the control technique uses a "stepping drive" or actuator which can incrementally change a parameter, such as the position of the control rods, by a fixed amount, either plus or minus one unit. By changing the relative position of the control rods within the nuclear reactor, the reactivity of the reaction can be varied. In effect, the algorithm completes an evaluation of the state of the nuclear reactor in one time cycle and determines if the stepping drive or actuator should add, subtract, or make no change in reactivity. In addition, the algorithm uses digital topology permitting the use of non-linear response functions in the determination of the required change in reactivity.