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Thermo-Mechanical Study of the Near-field around a storage borehole in salt formations

Objective

The aim of "CPPS" test is to study the near field thermomechanical behaviour in deep layered salt around a borehole waste emplacement under thermal loading. This is of major importance for predicting the behaviour of radioactive waste storage particularly as regards to the temperature and the pressure that the canisters will have to withstand. The influence of marno anhydritic layers will be studied too.

The experiment is planned to include three tests in separate boreholes at Amélie potash mine (F), with identical heating probes but different types of thermal loadings and backfilling materials.
A prototype heater with an annulus between the heater and the borehole as small as possible (less than 5 mm) was installed in December 1991 in Mine Amelie. After a period of observation of the borehole creeping, the heater was turned on in May 1992. The heating power was a 2.4 kW. After 2 months the heating power was raised up to 4 kW in order to speed up the borehole creeping.

The convergency measurements of the gallery are strongly dependent on the air temperature. For example a five degrees increase of temperature multiplies by a factor 6 theconvergency rate. The horizontal and vertical displacements of the rock salt surrounding the experimental gallery have been measured in several places. Their difference can probably be explained by the influence of the horizontal marno anhydritic layers.

At the end of the first heating step the closure rate was very low. Three days after the increase of power the borehole was in contact with the probe. During the first step the maximum temperature was 120 C on the surface of the probe. During the second step the temperature has reached 200 C at this place and has nearly stabilized. At a distance of 70 cm from the axis of the probe the temperature reached 70 C.

The displacement of the rock salt reached 8 mm in surface and 4 mm at a depth of 2.65 m and nearly zero at a depth of 4.65 m.
Work programme:

1. CPPS 1: Emplacing of a prototype heater with an annulus between the heater and the borehole as small as possible (< 5 mm) and heating after having observed the borehole convergency.
2. CPPS 2: Emplacing of a heater with the annulus filled with crushed salt and immediate heating.
3. CPPS 3: Emplacing of a heater with an empty annulus and heating after having observed the borehole convergency.

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 (2)

GROUPEMENT D'INTÉRÊT POUR L'ETUDE DES STRUCTURES SOUTERRAINES DE STOCKAGE
France
Address
Route De Saclay, Ecole Polytechnique
91128 Palaiseau
Mines de Potasse d'Alsace
France
Address
11 Faubourg D'altkirch
68055 Mulhouse