• Andersson, Tom
• Laukkanen, Anssi
• Holmström, Stefan
• Auerkari, Pertti
• Rantala, Juhani

Abstract

The final disposal of the canisters containing spentnuclear fuel involves long term storage in a deepgeological repository. The canisters include a 50 mmoverpack (top layer) of oxygen free phosphorus doped(OFP) copper for corrosion protection. In storage thecanister is subjected to some heating by the residualactivity of the contents, requiring reliable predictionof safe creep life from the available rupture and strainproperties of the overpack that includes electron beam(EB) or friction stir welds (FSW) for sealing.Assessments of creep strain and rupture at relevantservice conditions are inevitably susceptible to any biasin the applied material models, the underlying materialdata and predictive tools. FSW appears to generallyproduce stronger welds, although significant creepweakening has been indicated in case of small scale rootdefects. In EB welds large grains and characteristicpatterns of solidification result in some anisotropicmismatch to reduce creep strength and increase strainlocalisation of welds. In this paper FSW and EB crossweld test results are assessed and compared for creepresponse. The models have been converted to comply withthe requirements for in-house Finite Element Assessment(FEA) code and used for simulating the FSW behaviour. Thesimulated strain response is compared with correspondingmeasurements in long term creep testing. The results ofthe simulations and material models are discussed in theview of targeted life span of the canister overpack.Observations are presented regarding the expected stress,strain and multi-axial constraint in the weldedstructure.

Topics

• impedance spectroscopy
• grain
• corrosion
• simulation
• Oxygen
• strength
• anisotropic
• copper
• defect
• finite element analysis
• creep
• solidification
• Phosphorus