RCC-MRx Type P damage assessment methodologies for the design of Nuclear fusion reactor components

The RCC-MRx (Design and Construction Rules for mechanical components of nuclear installations: high-temperature, research and fusion reactors) code is developed by the French Association for Design, Construction and Surveillance Rules of Nuclear Power Plant Components (AFCEN). RCC-MRx differentiates between the different type of component damage depending on the type of load set. A constant steady load results in Type P damage while a cyclic time varying load results in Type S damage. The work presented here deals with Type P damages. Two failure modes are of interest: immediate excessive deformation and immediate plastic instability. To prevent these failure modes, RCC-MRx presents an elastic, limit analysis and an elastoplastic approach. The elastic approach is guaranteed to give a safe but highly conservative design. The limit and elastoplastic approach require more computational effort and requires the availability of the relevant material properties. The latter approach leads to less conservative but still safe designs. Having a structurally safe and less conservative design is most of the time preferred because of issues of sustainability and cost. RCC-MRx has primarily been written for fission type nuclear reactors and process pressure vessels rather than for nuclear fusion reactors. Fusion reactors differ from fission ones both in the type of loading and also in the type of geometry. Some fusion reactor components have a box type shape rather than cylindrical or spherical as in fission type reactors and process pressure vessels. RCC-MRx has a section dedicated to the assessment of box type of structures. This paper considers the Type P damage rules for negligible creep and negligible irradiation applied to a simple hollow box section, modelled in cantilever mode under the action of various load sets. The results indicate that elastic analysis is the most conservative. Also, depending on overall deformation of the structure, the results show that the elastoplastic plastic instability rule limit may be reached before that of the elastoplastic excessive deformation rule. The elastoplastic rule for excessive deformation presents several challenges in its application and is discussed in more detail together with a methodology to overcome these difficulties. The finite element software Ansys® Academic Research Mechanical, Release 2023 R2 is used as the analysis tool.