Principles of nuclear power station control

Lecture notes are presented which were first distributed as part of a UKAEA introductory course on reactor technology held during November 1975. The material is presented in a manner which hopefully will enable recent graduates in science and technology to obtain a broad overall picture of the problems involved. A nuclear power station is only one element of a dispersed interconnected arrangement of other nuclear and fossil-fired units which together constitute the national 'grid'. Thus the control of any one station must relate to the objectives of the grid network as a whole. Economic and technological factors are shown to lead to a national power supply operating around 50 Hz. A precise control of the supply frequency is also motivated by economic and technological considerations, and it is achieved by regulating the output power of individual stations. In order to make the whole grid network stable in following the load, it is shown that a satisfactory practical criterion is for each station to be stable when operating in isolation with a variable load. As regards individual stations, several special control problems concerned with individual plant items are discussed; these include controlled reactivity insertions, temperature reactivity time constants and flow instability. A simplified analysis establishes a fundamental relationship between the stored thermal energy of a boiler unit (a function of mechanical construction) and the flexibility of the heat source (nuclear or fossil-fired) if the station is to cope satisfactorily with demands arising from unscheduled losses of other generating sets or transmission capacity. Finally, two basic control schemes for power station operation are described, known as coupled and decoupled control. Each of the control modes has its own merits, which depend on the proposed station operating strategy (base-load or load-following) and the nature of the heat source. (author)