Dynamic qualification of complex structural components of nuclear power plants

The safety requirements and the lack of accessibility for any future repair, impose the design requirement that the integrity of reactor components of nuclear power plants be assured for the lifetime of the plant. To meet this design requirement it is essential to qualify the component, i.e. prove its capability to perform the design function for the design life. In performing its design function, the component is subjected to both static and dynamic loads. The qualification for static loads is rather simple and reliable, but qualification for dynamic loads is complex and often uncertain. This is because analytical tools are often inadequate for a realistic dynamic qualification and exact structurally simulated experimental models are almost always difficult to build. In such a situation, methods using tests on simple experimental set-ups supplemented by conservative analytical back-ups must be evolved. This paper highlights the intricacies involved in the conservative dynamic qualification of the complex components by considering the example of the moderator sparger tube. This component is a perforated tube submerged in water and excited by flow. For such a case, a completely analytical or a totally experimental qualification is not possible. This paper describes a procedure by which the required dynamic characteristics such as added mass, damping and fluid forces are generated from simple experiments and the component is qualified by analysis using these data.