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Evaluation of Hydraulic Transfer between the Argillaceous Rock and the Excavations

Objective

The aim of the PHEBUS (Phenomenology of Hydrical Exchanges Between Underground Atmosphere and Storage Host Rock) project concerns the study of the hydrous behaviour of a clay formation around ventilated excavations. It consists of a modelling, a laboratory mock-up and an in-situ test carried out at Mol facility in Belgium.
In a first phase, this consists in developing methodological tests not on core samples but on remoulded highly compacted clays. This procedure provides an appropriate control of the hydrical and mechanical history of the sample, making possible to understand the real hydrous phenomena.
In a second phase, an in-situ test will be carried out to validate the mock-up results. Using an accurate apparatus, this phase allows to reach some parameters and their time-dependence that can't be measured on a mock-up. With this short scale, it will be possible to evaluate the usefulness of a gallery ventilation test and to assess its technical feasibility: air conditioning system, porous lining conception and planning.
Modelling of hydrical transfer has been achieved. The main parameters are the relative humidity of the air and the saturated clay permeability. The model shows that the desaturation effect will concern a few square metres area around the openings, sufficient to affect the clay mechanical parameters and so the mechanical interaction between the clay and the lining. Under repository conditions the desaturated area should be independent of the radius of the gallery.

The modelling was used to dimension the mock up apparatus. The specifications have been defined according to the safety regulations. The apparatus mainly consists of an oedometer and a controlled ventilation system. Both are under test before starting the experimental phase. The in situ test, blowing dry air into a borehole in order to desaturate the clay through a porous lining, has been roughly defined. The emplacement, the drilling mode and the peripheral instrumentation have been defined on the basis of the results from the model.
Work programme:

Modelling
This initial phase consists in developing a simplified model of the hydrical transfer, in isothermal condition and without mechanical coupling (constant volume and porosity). This allows to study the parameters sensibility and to propose a first evaluation of the hydrical behaviour of the clay medium under a ventilation effect (orders of magnitude of water fluxes, desaturation area and phenomenon duration) on the basis of the present data.

Mock-up tests
The mock-up tests aim to well understand the phenomenology of hydrical exchanges between a controlled humidity air and the initially saturated clay, and to validate the model. It consists in conceiving and manufacturing an apparatus to test under high stress a clay with a cylindrical opening in the centre that simulates the ventilated gallery. At the end of each test, the mock-up is dismantled in order to measure the hydrical state around the opening.

In-situ test
This phase will be carried out at Mol underground facility. It will consist in drilling an horizontal borehole with a porous lining and an adequate peripheral instrumentation. The ventilation of this borehole will be controlled (dry temperature and relative humidity) and the amount of extracted water measured. Simultaneously the measurement of the clay hydrical state around the borehole will allow to evaluate the desaturation line. The experimental results will be compared to the model predictions.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

NATIONAL RADIOACTIVE WASTE MANAGEMENT AGENCY OF FRANCE
Address
Rue Jean Monnet 1-7
92298 Chatenay Malabry
France

Participants (1)

BELGIAN NUCLEAR RESEARCH CENTRE
Belgium
Address
200,Herrmann Debrouxlaan 40-42
1160 Bruxelles