  Materials containing a high proportion of grain boundaries offer significant
potential for the development of radiation-resistent structural materials.
However, a proper understanding of the connection between the radiation-induced
microstructural behaviour of grain boundary and its impact at long natural time
scales is still missing. In this letter, point defect absorption at interfaces
is summarised by a jump Robin-type condition at a coarse-grained level, wherein
the role of interface microstructure is effectively taken into account. Then a
concise formula linking the sink strength of a polycrystalline aggregate with
its grain size is introduced, and is well compared with experimental
observation. Based on the derived model, a coarse-grained formulation
incorporating the coupled evolution of grain boundaries and point defects is
proposed, so as to underpin the study of long-time morphological evolution of
grains induced by irradiation. Our simulation results suggest that the presence
of point defect sources within a grain further accelerates its shrinking
process, and radiation tends to trigger the extension of twin boundary
sections.
