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NF-PRO – Influence of THM-GCh Behaviour of the Bentonite Barrier
on the Corrosion Processes of the Carbon Steel Canister
Elena Torres 1 , Alicia Escribano 1 , María Jesús Turrero 1 , Pedro Luis Martín 1 , María Victoria Villar 1 ,
Javier Peña 1 , Juan Luis Baldonedo 2 , Paloma Gómez 1
Summary
1 CIEMAT, Madrid, Spain
2 UCM, Madrid, Spain
The effects of the reactions occurring in the canister/compacted bentonite interface should be
understood for assessing the waste isolation. THM parameters and geochemical conditions of
the clay barrier will vary during the performance of the repository. The experiments performed
by CIEMAT within the framework of NF-PRO project are based on a series of short,
medium and long term experiments conceived at different scales. They were designed in order
to provide useful information about the interaction between the clay barrier and the metallic
canister under realistic conditions. Results obtained in short term experiments show the existence
of a saline front moving towards the heater. The analysis of corrosion products show
that the initial precipitation of chloride plays a relevant role in the first stages of the corrosion
process, as it helps to initiate the nucleation of goethite. When bentonite at the interface gets
desiccated, goethite transforms into hematite.
1. Introduction
The effects of the reactions occurring in the canister/compacted bentonite interface should be understood
for assessing the waste isolation Thermo-Hydro-Mechanical (THM) parameters and Geochemical
(GCh) conditions of the clay barrier will vary during the performance of the repository.
Depending on the relative humidity, density and degree of saturation of bentonite will change. The
water content of the bentonite close to the canister and the increase in temperature due to the decay
of high level nuclear wastes will condition the corrosion mechanism of the overpack. The advance
of salts towards the hottest part of the barrier could favour the occurrence of localized corrosion if
anaerobic conditions have not been achieved.
The experimental studies realized by CIEMAT, within the framework of NF-PRO project, are focused
on the study of the carbon steel/bentonite interface and are based on a series of short, medium
and long term experiments conceived at different scales, from conventional laboratory experiments
and experiments in cylindrical cells, to those specifically designed 3D mock up experiments.
The aim of this work is to study the influence that thermo-hydraulic properties of the bentonite has
on the geochemical evolution of clay barrier and how the coupling of both conditions corrosion of
the carbon steel canister.
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