Introduction

8.5. A nuclear power plant consists of a number of systems which in­teract with one another in various ways. Knowledge of these intersystem interactions is essential for the design and operation of the plant. The systems themselves represent applications of the principles described in the previous and subsequent chapters of this book. We believe that it is useful at this point to introduce the system concept as applied to nuclear power plants and to indicate some of the intersystem dependencies. As energy transport, fuel management, safety, and other topics are presented in subsequent chapters, the reader can then be alert to the integration of the subject matter in plant applications.

8.6. The term system may be defined as a group of interrelated elements, or subsystems, forming the “whole” in a regular, organized manner [2]. In engineering design, the concept lends itself to mathematical modeling in which the interrelationships can be expressed formally for purposes of design optimization. Nuclear engineers also use such a systems modeling approach for probabilistic risk analysis (§12.206 et seq.).

8.7. Just what constitutes a system or subsystem depends on the need for analysis of the interdependencies that may exist. A system may have

many subsystems or parts which, in turn, could have within them “sub­subsystems,” usually referred to merely as subsystems. Where does this subdivision stop? The key question is whether the needs of the problem at hand require further subdivision. If not, the constituent part is referred to as a component.

8.8. Unfortunately, the term system is often used loosely to refer to any collection of components even if the grouping is, in fact, a subsystem. For example, manufacturers’ literature for some pressurized-water reactors de­scribes the reactor coolant “system” as within the Nuclear Steam Supply System. Also described are auxiliary fluid systems and electrical, instru­mentation, and control systems. Systems for waste processing, fuel storage, and ventilation are also covered. To be consistent with such practice, we will refer to both specific systems and subsystems as “systems” but indicate their hierarchial relationship as appropriate. The nature of some of these systems will be reasonably clear based on the material already presented. Others will become clearer as subsequent chapters are read.