Extended periods of interim storage are more relevant in Germany due to delays in the siting procedure to establish a deep geological repository for spent nuclear fuel, high level radioactive waste and in low/intermediate level waste container storage designated for the Konrad repository. BAM is involved in national cask licensing procedures and responsible for the evaluation of cask-related long-term safety issues.
The long-term performance of elastomer seals for lid systems of transport and storage casks, whether used as auxiliary seals in spent fuel casks or as primary seals for low and intermediate level waste packages, is an important issue in this context. The polymeric structure of these seals causes a complex mechanical behavior with time-dependent sealing force reduction.
The results of a comprehensive purpose-designed test program consisting of basic compression and tension tests as well as relaxation tests on unaged specimens of representative types of elastomers (fluorocarbon rubber (FKM) and ethylene propylene diene rubber (EPDM)) at different temperatures and strain rates are presented. They were used to identify the constitutive behavior and to obtain parameters for finite element material models provided by the computer code ABAQUS®. After estimating the influence of parameters such as Poisson’s ratio and friction coefficient by sensitivity analyses, the chosen values for the finite element simulation were validated by comparison with specimen test results.
Based on this preliminary work the simulation of a specific laboratory test configuration containing a typical elastomer seal with circular cross section is presented. The chosen finite element material model and the related parameters had to show that they are able to represent not only the specimen behavior under predominantly uniaxial load but also the more complex stress states in real components. Deviations between the measured and calculated results are pointed out and discussed.
The results from this work will be utilized in future simulations of aged elastomer behavior.