Mastering Requirements on Containment Boundary

For B(U)-F packages, IAEA 96 regulation requires no brittle fracture risk down to - 40°C for containment system and multiple high standard water barriers in order to consider water exclusion. Thick forged body with two leak tight lids are accepted as adequate by the French Authority to meet these requirements if sufficient margins does exist regarding brittle fracture on all their components including the bottom to shell welds. To exclude this risk for thick forged body, ferritic carbon steels dedicated to cryogenic application had been selected by Orano TN, with the following standard practices: a qualification of the material, a brittle fracture analysis, a qualification of the process. The qualification of the material includes the definition of the dynamic minimal toughness at -40°C with high loading rates. The obtained values for Orano TN forged steels and welds are very much higher than the one obtained with many other materials used for cask applications, such as for example ductile cast iron. The brittle fracture analysis considers the 1.4 additional minimal safety factor required by IAEA Tecdoc 717. In addition, as required by the French safety authority, the justifications deal with stress concentration areas like basket key grooves, bolts hole and any adjunction to the package (9 meters drop on the transport frame). The qualification of each manufacturer process (forged parts and weld) with an extend mechanical test program on the first part of each type of cask with the aim of detecting the weakest zone which will be used for the testing in serial production. - a volumetric ultrasonic examination with EN 10228-3 quality level 3, more stringent than the flaw size considered in the brittle fracture analysis. Furthermore, an extensive review was performed on more than 300 forged parts produced by Creusot Forges over 30 years. It showed the robustness of the manufacturing process and helped to the continuous improvement of the state of the art in terms of quality requirements. Altogether additional safety margins are established so that Orano TN forged casks are a unique and robust solution to face future evolution of international or national requirements.