Landfilling

Analysis of the long-term behavior of clay-bentonite-systems

The primary focus was the investigation of the long-term behaviour of clay-bentonite systems using natural salt clay. The resulting conclusions are of significance, e.g. for the safe storage of radioactive wastes in underground repositories.

 

Summary

Since radioactive wastes represent a potential hazard to the environment, they must be subject to particularly close monitoring. The long-term isolation of these wastes is to be undertaken in underground repositories excavated in salt rocks. Clay/bentonite has been selected as a sealant, since these materials show low hydraulic conductivity, high swelling pressure and a high buffer capacity under saline conditions.

 

The objective of these investigations was to determine the following:

  • the long-term behaviour of clay-bentonite systems (to be established using salt clay in a saline environment),

 

  • the sealing properties of clay plugs,

 

  • the retention properties of composite mineral systems in response to the action of salt solutions.

 

Results:

  • Although highly concentrated salt solutions increase hydraulic conductivity by 1 – 2 decimal powers, swelling pressures are reduced by approximately 50%.

 

  • Bentonite sealing elements with a high ratio of length to diameter can be used as redundant elements to fulfil the role of static abutments, since they dissipate the load by the action of swelling and wall friction, and adjust to loads applied as a result of natural reconsolidation.

 

  • Preswelling can be obviated by the incorporation of air-dried, precompacted bentonite with a high dry density.

 

  • On the fluid side, a saturation chamber with salt rock debris is used to ensure that, upon the ingress of fluid, the dry bentonite only comes into contact with a saturated solution.

 

  • Die Zugabe von ca. 5 % mineralischem Hydroxylapatit verbessert das Rückhaltevermögen des Bentonits, da es seine hydraulische Leitfähigkeit verringert.

Project Participants

Implementing Institution

Technische Universität Bergakademie Freiberg

More Project Information

Project title: Material investigations for clay/bentonite-based multi-component systems for sealing and load reduction, with high retention capacity, for the secure long-term closure of underground repositories and final storage facilities in salt rocks

Project number: 02C0193/0

Project period: 1993 - 1997

Project region: Germany (Saxony)

Project contact:

Herr Prof. Dr.-Ing. habil. Sitz

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Source: German National Library of Science and Technology Hannover (TIB)