On ductility variation of ductile cast iron for spent nuclear fuel packages and its correlation with casting defects and material microstructure

This paper describes a study to correlate the variation in ductility in ductile cast iron to casting defects and cast iron's microstructure. A large set of tensile and fracture specimens taken from three inserts for the Swedish KBS-3 programme were tested. About half the tensile specimens were analysed by metallography and fractography to identify and size defects and microstructural variations. It was found that the elongation at fracture was reduced by casting defects in the form of magnesium–oxide films and to a lesser extent by the graphite properties. An elastic–plastic probabilistic fracture mechanics model that relates the variation in ductility to the size and shape of casting defects is presented. The agreement between computed and measured results is quite good.