Numerical simulation of HELICOFLEX® metallic seals ageing mechanism for spent fuel cask

In the framework of CEA, TECHNETICS GROUP France, GNS and CRIEPI collaboration an experimental program has been carried out to assess the long-term use of HELICOFLEX® metallic seals in nuclear spent fuel storage casks. Accelerated ageing tests performed with the use of 120 mock-ups has provided more than 440 points measured over 12 years at different temperatures, which is relevant to address behaviour scattering from a statistical point of view.Beside this 100,000 hours experimental ageing program and the related consistent database, extensive work has been dedicated to the development of a numerical model using finite element analysis to be able to study seal ageing mechanisms and allow extrapolation of seals behaviours, like residual linear load or spring-back, to various ageing conditions and seal designs. Thus, following fundamental material characterization, a specific 3D digital model of HELICOFLEX® seals has been developed to describe its relaxation mechanisms and its relevance has been validated by comparison with the available experimental database.Beyond the analysis of a nominal seal design, the presentation shows the latest developments on analyses techniques, which aim to address seals behaviour reliability with numerical analysis. This work is built on numerical models developed a few years ago which are now completed by design of experiments and model reduction sampling techniques to consider uncertainty propagation regarding the seal and its environment. The analysis aims to assess the influence of geometrical tolerances related to seals and grooves as well as specifications related to mechanical behaviour range in material supply on seals properties. The results are then a range of expected behaviours, which are compared with the available experimental database scatterplot. This approach completes the experimental database by an informed evaluation of the influence of uncertainties on product reliability.