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AFCEN Codes are used as reference for nuclear components in over 100 power plants currently in operation (92), under construction (21) or in planning stages (7) around the world. Information on how AFCEN Codes are used around the world during planning, design, construction and operation of different reactors is provided in detail here (afcen, 2020a). In addition to these formal applications of AFCEN Codes, they have also served in France for designing many other nuclear facilities like nuclear steam supply systems for marine propulsion. AFCEN is an organization of operators, manufacturers, equipment suppliers, organizations, consulting firms, training providers, actively involved not only in the French but also in the international nuclear industry. In 2018, AFCEN has more than 67 institutional members, representing more than 650 experts who contribute to the development and continuous improvement of AFCEN Codes at international level. In 2018, 126 nuclear power plants and experimental reactors were currently designed and/or built using AFCEN Codes. The international AFCEN association proposes a complete codes collection for the design and

This paper gives an application case of the RCC-MRx mechanical design code for nuclear components in the domain of significant creep. It could be seen as a guide for engineers who have to perform mechanical creep and creep-fatigue analyses with this code. The application case is a spherical shell with an internal radius of 1250 mm and a thickness of 50 mm, which is made in AISI 316L. The structure is assembled by manual arc welding of plates using 19Cr-12Ni-2Mo type rods. The shell is intended to operate at 550°C mean temperature under an internal pressure of 5 MPa due to argon gas (the atmospheric pressure is considered outside). During operating, the internal temperature is equal to 600°C and the external temperature is 500°C. The shell is periodically stopped for servicing: during these periods, the temperature is 50°C and uniform, and the internal pressure is equal to the atmospheric pressure. A cycle is defined by a 500 h dwell time at 550°C followed by a 24 h arrest at 50°C; transient temperatures, thermal shocks during starting and arrest are neglected. The application of the RCC-MRx is shown for different damages, such as: - Excessive strain, plastic instability and rupture for primary loadings (negligible and significant creep); - Ratcheting, fatigue, creep-fatigue for all type of loadings. The effect of welds on expected life (creep, fatigue), and the comparison of calculated lives and allowed operating cycles for 316L and 316LN are described.

The paper describes the design rules for ratcheting in the 2012 edition of the RCC-MRx Code issued in French and English versions by AFCEN (French Association for the rules governing the Design, Construction and Operating Supervision of the Equipment Items for Electro Nuclear Boilers). For austenitic stainless steels, the RCC-MRx Code uses the efficiency diagram concept to evaluate an effective primary stress, Peff. Peff is defined as a virtual stress that applied alone would cause the same strain as the combination of the primary static stress and the secondary cyclic strain really applied. This concept is extended to significant creep domain and includes corrections to take into account structures cases presenting secondary membrane stresses (e.g. cylinders subjected to axial thermal gradients varying with time and space) or short duration overloads (as a level A seismic load, or an overload due to rapid drain-out caused by a sodium-water reaction). An alternative 3Sm design rule is proposed for all materials in the case of non-significant creep damage.