Euradwaste '08 - EU Bookshop - Europa

in the underground laboratory in Grimsel (Switzerland). The hydration of the buffer has progressed
more or less as expected although the rate of hydration became slower than initially predicted by
THM models after approximately 3 years. NF-PRO has extended the in-situ test data base for three
years more, which helped to assert the previous observations as well as the comparison with the
computational model for a longer period of time. However the information provided is still limited
for the judgement the long-term performance of the clay buffer due to its slow evolution.
The modelling within the component has been carried out of several groups with different objectives
using different modelling tools. The focus has been on:
Analysis of the FEBEX in-situ test
Analysis of the FEBEX mock-up
Addition of new processes into existing models
Analysis of moisture movement in TH-tests
THM-analysis of a deposition hole for spent fuel
The experimental work on gas migration in bentonite has been focussed around the Lasgit experiment
in the Äspö Hard Rock Laboratory. Lasgit uses a full scale KBS-3 deposition hole A full-scale
canister has been modified for the Lasgit experiment with twelve circular filters of varying dimensions
located on it’s surface to provide point sources for gas injection, mimicking potential canister
defects. These filters can also be used for hydraulic testing and to inject water during the hydration
phase. A large scale bentonite experiment means that a substantial amount a time needs to be devoted
to the saturation. Despite this, during NF-Pro a preliminary hydraulic test and a preliminary
gas injection test have been performed in the Lasgit. A preliminary model has also been developed
to understand how the fluid flow is coupled to the deformations that may take place in the Lasgit
experiment.
The compaction and permeability behaviour of crushed salt/bentonite mixtures have been studied
experimentally both at room and elevated temperatures through:
Principal compaction behaviour with strain controlled oedometer tests (85/15 and 90/10 mixtures
at T = 70° and 100 °C).
Advanced knowledges of the spatial state of stress with triaxial compaction tests (85/15 and
90/10 mixtures at T = 50° and 100 °C, 85/15 mixture at T = 70°C).
Porosity/permeability behaviour with combined compaction/permeability tests at room temperature
(80/20 mixtures with a maximum grain size diameter of 8 and 16 mm, respectively, at
T = ~32 °C).
Analysis with respect to earlier results.
The permeability of 80/20 or 85/15 mixtures of crushed salt and bentonite is reduced at room temperature
in comparison with pure crushed salt up to four orders of magnitude for equal void ratios.
At 90/10 mixtures, the reduction is only two orders of magnitude.
The laboratory investigations on the behaviour of pre-compacted salt bricks were focused on the
following issues:
Triaxial compression and permeability tests at different confining pressures on highly precompacted
crushed salt samples.
Gas injection tests on fluid saturated salt bricks with respect to 2-phase properties (e.g. permeability
and threshold pressure).
Long term hydrostatic compaction tests with and without added brine, respectively.
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