51313-02717-ACSIS: Model to Assess Potential for Atmospheric Corr. of SS ILW Containers in Storage & Operation

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Product Number: 51313-02717-SG

ISBN: 02717 2013 CP

Author: Fraser King

Publication Date: 2013

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A model has been developed to assess the potential for the atmospheric corrosion behaviour of stainless steel LILW containers in storage and during the operational phase of a geological disposal facility (GDF) in the UK. The model Atmospheric Corrosion of Stainless Steel in Stores (ACSIS) can be used to predict the extent of localised corrosion and stress corrosion cracking (SCC) and equally importantly to inform store designers and operators how to avoid atmospheric corrosion through appropriate control of environmental conditions.

The model accounts for the initiation and propagation of localised corrosion (either pitting or crevice corrosion) and SCC of austenitic or duplex stainless steel containers as a result of the deliquescence of surface salt contaminants. The code first characterizes the time-dependent nature of the corrosive environment in terms of the duration of and interval between wetting events based on temperature and relative humidity data from the store or GDF and knowledge of the nature of the surface contaminant. Various criteria are used to determine whether localised corrosion and/or SCC initiate during a given wetting episode and if initiation does occur the extent of damage that may result. The output of the model includes the number of corrosion episodes and the depth of the pit crevice and/or crack.

A preliminary version of the model has been developed and simulations have been run for hypothetical environmental conditions in a UK store and GDF. For this preliminary model the containers are assumed to be contaminated by a single salt. Localised corrosion and SCC are assumed to initiate above a threshold temperature with any damage conservatively assumed to accumulate at the same site for consecutive wetting episodes. The results of the model simulations will be discussed both in terms of the characterization of the time-dependent environmental conditions and the consequences for the corrosion behaviour of the containers. Future developments of the model include the incorporation of the effects of mixed salt contaminants (both in terms of the threshold conditions for deliquescence and the time-dependent composition of the aqueous phase) alternative initiation criteria for localised corrosion and SCC (e.g. based on the concept of a threshold potential) and/or alternative treatments of the accumulation of damage for consecutive corrosion episodes. An experimental program is under way to support these improvements to the model.