<title>Abstract</title> Enhancing radiation tolerance in materials is at the forefront of materials science. Grain and/or phase boundaries in nanocomposite, nanophase, and nanofoam materials have been shown to provide a promising route to enhancing radiation tolerance. Here, through a combination of positron annihilation spectroscopy, transmission electron microscopy, and computer simulation, we show that pre-existing voids in bulk single phase Fe without the incorporation of nanograins or nanotwins provide sinks …