Revision of the Annex Z V Concerning the Calculation of Bolted Joints in the French Nuclear Code RCC-M®

Abstract

AFCEN is the publisher of the French Nuclear code RCC-M® (Design and Construction Rules for Mechanical Components of PWR Nuclear Islands) [1]. It has launched an action for the revision of the Annex Z V and F 7000, respectively concerning the design and the installation of the bolted flange connections. It should be published as probationary phase rules (Section VI of RCC-M®), in the next version of the code, in 2022. The proposed modifications for F 7000 have already been described in [2], and this paper focuses on the proposed modification for the calculation method detailed in the Annex Z V. First, the general philosophy and structure of the Annex, including both Taylor-Forge based (Z V 2000) and NF EN 1591-1 [3] based (Z V 3000) calculation methods, is introduced. Then the major proposed improvements introduced in Z V 2000 (Taylor-Forge based), compared to current edition, are detailed. This includes the management of the metal-to-metal contact (MMC) in the connection (between flanges or between flanges and the gasket limiter ring) that can be required in both assembly and operation. Moreover, the use of specific gasket types involved in these connections (Expanded Graphite Ring or Metal Energized C-Ring...) is covered in this paper. Finally, a focus is also performed on other introductions, like the management of standard connections (including standard flanges, gasket, and bolts), the account for the tightening scatter, the effective gasket width determination in regard with the flange rigidity, and the internal force variation in the connections due to thermal expansion.