Considerations in the control of PWR-type multimodular reactor plants

Issues in the control of PWR-type multimodular reactor plants are discussed with emphasis on the need for operation under conditions of unbalanced loads, operating strategies for both single- and multireactor systems, and the coordinated adjustment of power and temperature. One defining characteristic of a multimodular plant is that each unit will probably be loaded differently so as to compensate for the effects of varying maintenance outages and, if desired, to stagger refuelings. A second characteristic is interdependency in that, with several reactors connected to a common turbine, a change in any one unit will propagate to the others. The combination of these two factors makes operation of a multimodular plant differ from that of existing single-reactor ones. For example, conventional sliding-T/sub ave/ load maps cannot be applied directly to a multimodular system because, with the exception of the highest-powered unit, each reactor´s temperature will be a function of not only its power level but also that of the most heavily loaded one. Similarly, withdrawal of the control rods in a fully loaded PWR will, in the presence of a large negative temperature coefficient, cause hot and cold leg temperatures to rise but leave power and core /spl Delta/T unchanged. In a multimodular system, there will be a shift in power to the affected reactor. These and other differences in the behavior of multimodular and single-reactor systems are delineated. The paper concludes with some practical suggestions on the operation of PWR-type multimodular plants.<>