Ratcheting Predictive Methods in RCC-MR Code

Abstract

The structures belonging to Gen IV reactors such as Sodium Fast Reactors (SFRs) and High Temperature Gas Reactors (HTGRs) are submitted to high temperatures and high thermal gradients and must be designed against the risk of ratcheting. RCC-MR code has been developing for several years original methods to deal with this damage mode. The last edition of the code has been issued in French and English versions on October 2007 by AFCEN. It constitutes the result of a continuous and important work to develop and improve design and construction rules. To deal with ratcheting damage mode, the “efficiency diagram” method is used. This method has been improved with time as a function of experience and R&D work and it is able to get a good prediction of ratcheting in all specific phenomena occurring in high temperature reactors: - Cases where high thermal membrane stresses are present. Such problems appear particularly at the free level zone of shells in SFRs for which ratcheting risk has been proved. - Cases involving short-term overloads, representative of seismic cycles and pipe draining operations, for which ratcheting appears to be less damaging than permanent overloads of same amplitude. The objective of this paper is to describe the original methods used in RCC-MR code, the process of development and improvement, helped by the R&D work, leading to the present 2007 edition.