Mod 9Cr1Mo Steel (grade 91) is one of the materials envisaged for the Reactor Pressure Vessel of Very High Temperature Reactors. To avoid the implementation of a surveillance program covering the monitoring of the creep damage throughout the whole life of the reactor, it is recommended to operate the Reactor Pressure Vessel in the negligible creep regime. In this paper, the background of negligible creep criteria available in nuclear Codes is first recalled and their limitations analyzed. Then, guidance for deriving criteria more appropriate for mod 9Cr1Mo steel is provided. Finally, R&D actions in the U. S. and France to support the new approaches are discussed and recommended.
Volume Subject Area:Materials and Fabrication
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