8.17. The systems concept is a useful design tool for the analysis of how component and subsystem failures can propagate and affect performance.

For example, in a PWR, a reactor coolant pump could fail as a result of an electrical fault. The resulting reduction in flow would, in turn, raise the core water temperature, possibly cause boiling, then raise the fuel tem­perature, all of which would affect the reactivity as determined by the appropriate coefficients. This, and similar chains of events, can be treated analytically. Thus, a systematic study of intersystem dependencies provides the designer with a thorough examination of various modes of system response which would not otherwise be apparent.

8.18. Fault tree and event tree analyses (§12.213) are related analytical procedures for assessing the reliability of safety-related systems. As will be discussed in Chapter 12, these approaches are valuable decision tools for identifying “weak links” in intersystem functional dependencies.