A potential post-closure release of radionuclides from a KBS-3 spent fuel repository depends on the failure modes of copper canisters. It is generally accepted that a combined erosion/corrosion case and future large earthquakes could cause such failures. In paper, we address other proposed failure modes, not by assessing their relative merits but rather their potential consequences. It is judged that a hypothetical poor creep ductility of copper would have the largest potential consequences.