Elastomer seals are used in many industrial applications due to their excellent mechanical properties at a wide range of temperatures. Their high versatility and recovery potential under several load conditions make them well suitable for the application in containers designed for transport and disposal of radioactive materials. In containers for low and intermediate level radioactive waste they are used as barrier seals, in spent fuel storage and transportation casks (dual purpose casks (DPC)) as auxiliary seals. While a seal exchange at defined intervals is typical in many conventional applications, it is impossible or at least hard to perform when principles of minimization of radiation exposure have to be considered and prohibit an unnecessary cask handling. An extensive knowledge of the change of the elastomer’s properties during aging and the availability of reliable end-of-lifetime criteria to guarantee the permanent safe enclosure of the radioactive material is mandatory. As BAM is involved in most of the national cask licensing procedures and in the evaluation of cask-related long-term safety issues, great efforts have been already made and are still planned to scientifically support this task.

Compression stress relaxation (CSR) and compression set (CS) were identified as key indicators of elastomer long-term performance and quantitatively investigated in comprehensive test programs. Among other representative types of elastomers, specimen made from ethylene propylene diene rubber (EPDM) were tested before, after and during aging to capture the most important of their complex mechanical properties.

In the presented study, exemplary results were used to simulate the compression stress relaxation and the compression set of elastomer O-rings during aging. Regarding the influence of temperature, the time‑temperature superposition principle is applied in the relaxation analysis of elastomer O-rings. The proposed model is implemented in the commercial finite element software ABAQUS/Standard^®^ with a sequential temperature displacement coupling. Numerical results match well the experimental compression stress relaxation measurements. The prediction of compression set values after long-term aging show a relatively good agreement with the experimental results. Nevertheless, all input parameters derived from the specimen tests, additional assumptions concerning boundary conditions and modeling strategy are discussed with regard to the identified slight discrepancies.

The possibility to extend the finite element model to represent the O-ring seal’s ability to recover after a (fast) partial release is taken into account.


Numerical Modelling of Compression Stress Relaxation and Compression Set of Elastomer O-Rings During Aging

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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