fundamental understanding of the interactions between point defects and grain boundaries (GBs) is critical to designing radiation-tolerant nanocrystalline (nc) materials. An important consideration in this design is sink strength

which quantifies the efficiency of a sink to annihilate point defects. Contrary to the common belief that random high-angle GBs provide the upper limit for rate of defect annihilation

here we show that the sink strength of low-angle GBs can exceed that of high-angle GBs due to the effect of GB stress fields. This surprising finding provides a novel opportunity to enhance the radiation resistance of nc materials through GB engineering.