This paper provides a short summary of investigations that have focused on the occurrence of the phenomenon that is commonly referred to as atmospheric chloride-induced stress corrosion cracking (AISCC) in types 304L and 316L austenitic stainless steels; the materials from which storage containers for the UK's intermediate level nuclear waste are currently fabricated. A brief overview of the relationship between localised corrosion phenomena (pitting or crevice corrosion) and stress corrosion cracking from observations derived under conditions of immersion in chloride-containing environments is provided. The impact of environmental variables such as the relative humidity, temperature and chloride deposition density on the development of AISCC and potential difficulties in extrapolating data derived from laboratory investigations to an in-store situation are also discussed. Proposals for the development of laboratory protocols that may more accurately reflect behaviour in an actual storage situation, including the possibility of employing accelerated testing methods, are also briefly addressed.

Geological repository designs employ a multi-barrier approach. The materials, which include wasteforms, backfill and host rock, are typically porous quasi-brittle. Mechanical damage (e.g. nucleation and growth of microcracks) can result in significant changes in permeability. A knowledge of how the permeability is affected is critical to accurate modelling of radionuclide transport. This work proposes a novel 3D lattice-type model for the damage evolution in such materials, referred to as the site-bond model. Its advantages over previous models are that the shape of the lattice cell is physically realistic and that any macroscopic elastic response can be represented, including those of cementitious and geological materials. Damage accumulates as bonds fail upon reaching prescribed failure strengths. These are dictated by a predefined pore size distribution. Concrete is used as a study material. It is demonstrated that the model can predict the macroscopic stressÀstrain response under unconfined tension and compression with emergent non-linearity due to damage evolution. Ongoing work on the prediction of permeability changes with damage is discussed. This is based on the interaction between the model proposed here and a lattice model of the pore space.

This study focused on the effect of organic species on the occurrence of atmospheric-induced stress corrosion cracking (AISCC) in intermediate level waste (ILW) container materials under 'wetted' deposits of artificial sea-water (SW). Artificial SW solutions enriched with one of two bioexudates -with organic carbon concentrations of between 92 and 451 mM -were employed to investigate changes in interfacial behaviour, associated with organic content, at the liquid-solid boundary on type 304L stainless steel (SS). These effects were determined in terms of contact angle and deposit diameter. On evaporation organically-enriched SW droplets deposited on 304L SS maintain a constant contact diameter on exposure to a relative humidity (RH) of 70¡1%. By contrast deposits produced from artificial SW alone contract radially inwards. The bio-exudate that remained on the SS surface following the cleaning of deposits formed from organically enriched SW was visualised via cyanoacrylate fuming. This technique confirmed that bio-exudate adheres to 304L SS after removal of the inorganic components. The impact of organic enrichment on AISCC was investigated using droplets of test solutions on 304L U-bend specimens exposed to environmental conditions of 50?0¡0?5uC and 30¡1% RH.

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