Title: A Probabilistic Methodology to Determine Failure Probabilities and Acceptance Criteria for the KBS-3 Inserts under Ice-Age Load Conditions
Authors: NILSSON KARL-FREDRIKNILSSON FredDILLSTROEM Peter
Citation: NUCLEAR TECHNOLOGY vol. 163 p. 3 - 14
Publisher: AMER NUCLEAR SOCIETY
Publication Year: 2008
JRC N°: JRC35107
ISSN: 0029-5450
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC35107
Type: Articles in periodicals and books
Abstract: The Swedish KBS-3 copper-cast iron canister for geological disposal is in an advanced stage. This reports deals with the cast iron insert that provides the mechanical strength of the canister and outlines an approach to assess the failure probabilities at large isostatic pressure (44 MPa) for manufactured canisters that could occur during future glaciations and how to derive acceptance criteria to ensure that failure probabilities are extremely small. The work includes a statistical test programme using three inserts to determine the tensile, compression and fracture properties. Specimens used for material characterization were also investigated by micro-structural analysis to determine the microstructure and to classify and size defects. It was found that the material scatter and low ductility was caused by many defect types, but with slag defects in the form of oxidation films as the most important one. These data were then used to compute defect distributions and as direct input to FE-calculations of KBS-3 canisters. A large number of FE-analyses were performed at the maximum design load (44 MPa) covering distributions of material parameters and geometrical features of the canisters. The computed probabilities for fracture and plastic collapse were very low even for material data with poor ductility. Two large scale isostatic compression tests of KBS-3 mock-ups to assess safety margins are also described. The failure occurred at loads above 130 MPa in both cases, indicating a safety margin of at least a factor three against the maximum design load. As a result of the project new acceptance criteria have been defined for insert geometry and material properties and the manufacturing process for inserts have been modified to ensure that these criteria are always fulfilled.
JRC Directorate:Energy, Transport and Climate

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