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Impact of Thermo-Hydro-Mechanical Processes on Repository Performance
Summary
Patrik Sellin 1 , Hans-Joachim Alheid 2
1 SKB, Sweden
2 BGR, Germany
The purpose of the RTD C3 in the NF-Pro project was to improve the degree of understanding
of the thermo-hydro-mechanical and geochemical (THM(C)) processes in the near-field in an
integrated way to enhance the predictive capability of the existing models, especially in relation
to their link with safety functions and the assessment of long-term safety. The focus was
put on a few selected THM(C) processes:
The saturation of a bentonite buffer
Gas migration in/through a bentonite buffer
Compaction properties of a crushed salt backfill
The main focus of the work was to improve the handling these processes in long term performance
assessment, but issues on EBS manufacturing has also been addressed.
1. Introduction
The primary aim of the engineered barriers is to isolate the radioactive waste from the rock and particularly
from the groundwater. Buffers and backfills (of some disposal concepts) will be exposed to
high temperature, significant temperature gradients, and pressure exerted by the canisters and by the
convergence of the emplacement drift. These factors combine to create conditions that determine
the short- and long-term performance and chemical stability and form the basis of the design of the
buffer/backfill with respect to composition, density and dimensions.
A number of projects and large scale experiments carried out prior to NF-Pro (for example FEBEX,
PROTOTYPE, OPHELIE, BAMBUS) have provided very valuable information and a significant
amount of data that is being used for the validation of THM numerical models. However the duration
of these tests has been yet relatively short compared with the slow evolution of the processes
involved. Also a number of questions remained in relation with some aspects such as the long-term
evolution of the bentonite properties and the effects of gas generation in a clay buffer. In the case of
buffers made with compacted salt grit, there are still open questions concerning the compaction
process at low porosities and development of permeability in the buffer. Clay-salt mixtures may
help to guarantee an instant sealing of the buffer even at times when compaction is not yet completed
but the THMC behaviour of such mixtures were not well analysed. Joints between blocks
and with the rock are possible pathways that also may have to be considered.
For these reasons, a comprehensive analysis of the THM (C) processes in the EBS have been carried
out in RTD Component 3 in NF-Pro, considering different types of buffer material (bentonite,
salt), different scales (from laboratory to repository scale), and different degrees of saturation and
thermal states. This paper is a brief summary of some of the activities and conclusions from the
work within the RTDC [1].
2. Objectives
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