A350 LF5 Cl2 a convenient material for containment of type B package

For the containment of Type B packaging it is necessary to demonstrate that there is no risk of brittle fracture. For ferritic carbon steel, the brittle facture risk assessment is based on toughness properties and the size of critical discontinuities which can be detected by Non Destructive Examination. Cryogenic carbon steels are very good candidates and their price is very competitive since the Nickel content is limited. A350 LF5 class 2 base material with a nominal Nickel content of 1.5% has been used for several decades in the manufacturing of casks with forged thick components such as the TN®12-2 transport cask or the TN®24 dual purpose cask (DPC). The grade performances of this material are well optimized: Dynamic fracture toughness at -40°C as well as tensile properties at maximum service temperature ensures an adequate resistance in accidental transport conditions. This performance has been demonstrated thanks to a material qualification which has been completed by a forging process qualification for each first-of-a-kind component and/or new forged master. The acceptance criteria for the quality control of the serial production is based on a minimal Charpy energy value of 140 J at -40°C which guarantees a sufficient minimal dynamic fracture toughness at -40°C compared to the usual values of Stress Intensity Factors in a containment vessel during a 9-m drop. This approach has been validated by the French Nuclear Safety Authority (ASN). Its weldability is also very good. The toughness and tensile properties of the shell-to-bottom weld are as good as that of the base material. Thanks to these unique properties, A350 LF5 class 2 is a very appropriate material for the containment of Type B packaging.