Stability and Construction of Caverns for the Disposal of Cemented Low-And Medium-Level Wastes
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STABILITY AND CONSTRUCTION OF CAVERNS FOR THE DISPOSAL OF CEMENTED LOW-AND MEDIUM-LEVEL WASTES W. RAAB, C. FROHN, M.W. SCHMIDT Gesellschaft far Strahlen- und Umweltforschung mbH Mflnchen, Institut far Tieflagerung, Wissenschaftliche Abteilung, Theodor-Heuss-Str. 4, 3300 Braunschweig, FRG
ABSTRACT The geomechanical and mining-technological aspects of the construction of salt caverns as disposal chambers have been investigated during project phase 2, completed by mid 1981.
With a view towards the stability analysis of such a ca-
vern, FEM-estimates have been carried out and evaluated.
From these it
can be
derived that - a rotational ellipsoid would be the most suitable shape - its
dimensions should be 82 m (vertical axis) and 42 m (horizontal axis)
- the distance
(safety pillar) between the neighbouring caverns should be 170 m
(vertical) and 180 m (horizontal). For practical engineering purposes the rotational ellipsoid can be modified into a cylinder with conic bottom and top. The numerical model simulated the short term as well as the long term characteristics of the surrounding salt rocks.
The short term characteristics were assessed by an elastic approach,
the
long term characteristics by a rheological model. The input parameters have been determined by means of laboratory tests on ASSE rock salt. In a second step the characteristics of partially and completely filled caverns were simulated.
It
was shown clearly that deformation of the salt rock
comes to a halt when counteracted by the filling. Based upon the results of the stability analysis, investigations were made to find out a suitable mining technique for the construction of the cavern.
Solu-
tion mining and conventional development by means of drilling and blasting have been studied alternatively. vantages a decision in
Since both methods have their advantages and disad-
favour of the one or the other cannot be made until the
actual site has been defined.
INTRODUCTION A bulk disposal of low and medium level waste and a subsequent in
situ-solidi-
fication requires the preparation of stable boreholes for access to the caverns which are to serve as disposal cavities for the concrete monolith. During project phase 1 (1977 - 1978)
a disposal system has been developed in
accordance with the anticipated waste volume,
the resultant operating time of
880
the system, and the heat-release from within the product due to both the hydratization of the cement and the decay of the radioactive contents. 3
based upon caverns with some 75.000 m
The system is
effective volume employing rockmechanical
considerations that proceed from experience with comparable underground openings. During project phase 2 with a view towards its
(1979 - 1981)
this system had to be evaluated by GSF
stability and construction technology.
GEOLOGICAL POSITION The caverns should be constructed in
a virgin part of the salt dome.
Depend-
ing on the excavation technique to be applied, these caverns either can be constructed completely isolated from the accessibl
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