20th International Forgemasters Meeting - IFM 2017

The objective of this study is to develop the spent nuclear fuel shipping cask shell material and welding rods with high toughness at very low temperature. Recently, in Korea, The demand of shipping cask has been increased to transfer spent nuclear fuel and nuclear waste to an interim facility and store safely due to the limitation of the storage space inside nuclear power plant. The shipping cask is required to have excellent toughness for ensuring structural integrity even against hypothetical free dropping accident during transportation. In particular, in Korea, the shipping cask shell material and its weldment should be satisfied with the strict additional design requirement of Reference Temperature for Nil-Ductility Transition (RTNDT) of colder than -105oC to verify safety even in very low temperature environment. For SA350 LF3 low alloy steel using several small blocks, optimum alloy design has been performed through the optimization of chemical compositions such as C, Al and addition of boron. Also, optimum heat treatment process has been set up to get fine ferrite and austenite microstructure for improving toughness. Through the manufacture of the 30 ton cask shell forging with diameter of 1,900mm and wall thickness of 540mm, we can confirm that the cask material have excellent toughness satisfied with material specification of SA350 LF3 and RTNDT design requirement. Also, welding rods satisfied with RTNDT criteria of -105oC for GTAW, GMAW and SAW process have successfully developed through the alloy design and optimum welding heat input. Through this research, we can obtain the manufacturing technology of spent nuclear fuel shipping cask for Korean nuclear industry.