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Key Processes affecting the Chemical Evolution of the Engineered Barrier System
David Arcos 1 , Jaime Cuevas 2 , Ana Maria Fernández 3 , Horst-Jürgen Herbert 4 , Pedro Hernan 5 , Luc
Van Loon 6 , Pedro Luis Martin 3 , David Savage 7 , Nick Smart 8 and Maria Victoria Villar 3
Summary
1 Amphos XXI, Spain
2 Universidad Autonoma de Madrid, Spain
3 CIEMAT, Spain
4 GRS, Germany
5 ENRESA, Spain
6 Paul Scherrer Institut, Switzerland
7 Quintessa Limited, UK
8 Serco, UK
The NF-PRO project, completed at the end of 2007, has tackled key issues in the chemical
evolution of the EBS, through a four-year programme of laboratory experiments and computer
modelling, involving some 18 participants from 8 countries in the European Union and
beyond. Laboratory experiments ranged in physical scale from the ‘micro’ (millimetre scale)
to ‘macro’ (metre scale ‘mock-up’ experiments), whilst computer simulations aided interpretations
of laboratory experiments in ‘real’ time, and enabled the extrapolation of experimental
results to the timescales of relevance to waste isolation (up to a million years). Although not
strictly a component of NF-PRO, natural systems evidence has been used to place experimental
results into the relevant time context.
1. Introduction
The engineered barrier system (EBS) plays a key role in the long-term isolation of high-level radioactive
wastes (HLW) in deep geological repositories. Consequently, it is important to have a good
understanding of its chemical evolution with time. After repository closure, compacted clays acting
as ‘buffers’ around waste packages will resaturate and swell, forming a diffusive transport barrier
for potential canister corrodants, and in the long-term, for the migration of waste constituents.
Upon contact with saturating groundwater, canister metals will slowly corrode, initially under aerobic
conditions, and ultimately, anaerobically. In the long-term, the stability of swelling clays in the
EBS may be challenged by chemical interactions with other barrier materials, such as cement and
concrete, in situ groundwaters, and canister metals. Ultimately, the perforation of canisters by corrosion
will lead to radionuclide migration through the clay buffer via diffusion, and retardation by
sorption within the clay.
The principal objective of NF-PRO for the near-field evolution component was to establish the scientific
and technical basis for evaluating the safety function ‘containment and minimisation of release’
of the near-field of a geological repository for high-level radioactive waste and spent fuel. To
this end, NF-PRO investigated realistic processes and process couplings affecting the isolation of
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