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In Germany, the concept of dry interim storage in dual purpose metal casks before disposal is being pursued for spent nuclear fuel (SNF) and high level waste (HLW) management. The main safety relevant components are the thick-walled dual purpose metal casks. These casks consist e.g. of a monolithic cask body with integrated neutron shielding components (polymers, e.g. polyethylene) and a monitored double lid barrier system equipped with metal and elastomer seals. The metal seals of this bolted closure system guarantee the required leak-tightness whereas the elastomer seals allow for leakage rate measurement of the metal seals.
This presentation provides an overview of BAM proactive R&D projects related to the long-term behavior and degradation effects of metal seals, elastomer seals and polyethylene used as neutron shielding material. Particular attention is paid to the approach and first results of the third-party-founded research project LaMEP with the aim of further closure of existing knowledge gaps of safety relevant aging effects of such cask components.
Three-dimensional finite element analysis of O-ring metal seals considering manufacture tolerances
(2019)
Metal seals are widely used in various industrial branches with severe working conditions (e.g. high pressure, high temperature, corrosion, or radioactive radiation). For example, O-ring metal seals are applied in the closure lid system of transport and storage casks for radioactive materials to guarantee an approved specified leak-tightness and the safe enclosure of the radioactive inventory. Within safety assessments of those casks under normal or accident conditions during transport and long-term interim storage for several decades, numerical simulations of the thermo-mechanical behavior of metal seals by using finite element (FE) analyses are suitable and effective.
In general, finite element codes provide the possibility to construct a complex three-dimensional (3D) modelling of metal seals with solid elements, cf., where all components of the metal seals are modeled in detail. This modelling is complex but allows the consideration of underlying physical effects such as elastic-plastic deformation, thermal expansion, creep/relaxation, friction and possible local damage. Therefore, this approach permits the investigation and understanding of the complex behavior of metal seals in detail which can hardly be measured for all seal components.
In a prior work, the complex 3D modelling approach was applied to investigate the influence of each seal component on the global seal force by considering varying material properties and different seal diameters. In the present contribution, the influence of manufacturing tolerances is discussed. At first, the results of prior work are summarized. After that, the manufacturing tolerances of the studied O-ring metal seal types are described and the corresponding FE model with all individual components is introduced. Finally, the influence of varying manufacturing tolerances of each seal component on the global seal force is analyzed and discussed.