Lifetime evaluation of graphite components for HTGRs

摘要

The lifetime of material and/or components has been discussed individually from different concepts, and sometimes gives confusion to material researchers as well as designers. The lifetime of materials is determined based on the dimensional changes due to neutron irradiation, at which they return to their original dimensions after initially contracting. On the other hand, the lifetime of components for HTGRs is defined based on a margin of the specified minimum ultimate strengths of the graphite to the stresses induced in the components. As an example, the stresses induced in the graphite block for the HTTR were, then, compared with the limited stress value determined from the specified minimum ultimate strength, and the lifetime of the component was evaluated and compared with that defined as dimensional changes. As a result, it was found that the lifetime of components for HTGRs should be determined as the shorter one in the two lifetimes defined by the stress-strength relationship and by the dimensional changes.