Model for the Microbiological Corrosion of Copper Containers in a Deep Geologic Repository

Abstract

A model has been developed to predict the impact of microbiological processes on the long-term corrosion behaviour of copper containers in a deep geologic repository. The model accounts for a range of aerobic and anaerobic microbial processes. Various factors expected to limit the extent of microbial activity in the repository, such as the lack of water, evolving redox conditions, and the nutrient-poor environment, are taken into account in the model. Amongst other effects, the model predicts that microbial activity will not occur close to the container in the presence of highly compacted bentonite buffer material.

Microbiologically Influenced Corrosion of Nuclear Waste Containers

“…-elevated container surface temperature and resultant desiccation of the bentonite 25,30-31 -low water activity and/or high swelling pressure in saturated bentonite (dry density ≥ 1.6 Mg/m 3 ) 26-29 -low water activity due to saline pore fluids [28][29] -for thin-walled containers, the presence of gamma radiation 3,24 -limited availability and supply of nutrients in compacted bentonite [34][35]43 -absence of aerobic activity following consumption of the trapped atmospheric O 2…”

“…For bentonite-backfilled repository designs, King and co-workers [34][35]57 have developed a mathematical model to predict the spatial and temporal distribution of microbial activity and the consequences for corrosion of the container. Both microbial processes and abiotic corrosion reactions are described by kinetically based reaction-diffusion equations for various forms of microbe, nutrients, TEA, and reactants and products of the corrosion reactions.…”

“…[60][61][62][63][64][65][66] The microbial reaction scheme was selected for its relevance to the corrosion of copper containers, and included aerobic respiration, various components of the N cycle, fermentation, and sulfate reduction. [34][35]57 These reactions result in the consumption of O 2 , the formation of possible SCC agents for copper (nitrite, ammonia, and acetate), and the formation of sulfide, in the presence of which copper is thermodynamically unstable in water. In the model, limitations are placed on the kinetics of the microbial reactions based on the various environmental stressors discussed in the previous section.…”

“…This is unfortunate since, having seen damage, researchers have tended not to, or have been unable to, extrapolate the observed corrosion from these accelerated conditions to predict the extent of damage that would be expected under conditions in the repository. Lastly, with one or two exceptions, [32][33][34][35] there has been relatively little effort to develop predictive models for MIC and microbial activity in the repository. This is particularly concerning since, as noted above, it is necessary that the effects of microbial activity on container lifetimes be predicted, just as for any other form of corrosion.…”

Yucca Mountain engineered barrier system corrosion model (EBSCOM)

“…The RH is numerically equal to the thermodynamic water activity a W , a parameter that has been linked to the viability of different types of microbe [15]. Most microbial species are not active at a W < 0.96, and this water activity has been proposed as a threshold value for the modelling of microbial activity in nuclear waste repositories [16]. The time dependence of the RH (or a W ) in the drifts is not explicitly included in EBSCOM but, since RH and temperature are closely linked (Fig.…”