Analysis and evaluation of the irradiated dimensional and volume change behavior of nuclear graphites

Abstract

Literature on the changes in the specimen dimensions and volume after high energy neutron irradiation of more than a dozen graphites were examined. Some of these data have been previously used to design graphite components in gas cooled reactors. The dimensional change behavior of a graphite is rather unique and depends on both the irradiation temperature and accumulated irradiation dose. The characteristics of the dimensional and volume change behavior of several graphites were analyzed and evaluated from engineering design consideration of graphite components. Specifically, six parameters were derived from the dimensional and volume change behavior. These parameters can serve as “figures-of-merit” (FOM) to enable engineering judgement on the irradiation-induced dimensional and volume change behavior of nuclear graphites, and are referred to as “derived figure-of-merit (DFOM).” The DFOMs also provide engineering bases to examine the opportunity to select several competing graphites for fulfilling the design and operation of components in reactor service. The utility of these DFOMs can be realized potentially in designing inservice inspection and component condition monitoring (CCM) protocols that are effective and efficient both technically and economically. The DFOMs, in combination, also can guide the reactor operator to arrive at optimum component replacement schedule for graphite components, which ensure maintaining graphite components functional requirements and related reactor safety issues.