Properties and characteristic values

Opalinus Clay exhibits properties conducive to the deep geological storage of radioactive waste. The advantages clearly outweigh any disadvantages.

The advantages of Opalinus Clay as a repository material for the deep geologic repository are mainly due to its excellent capacity to bind and retain radioactive material over a very long time period.

  • With a hydraulic conductivity of 2 x 10‑13 m/s, Opalinus Clay is practically impermeable. Transport of radionuclides by fluids, such as water, can be ruled out for all practical purposes.
  • Due to their relatively high internal surface area (100 m2/g) and their electrical properties, clay minerals are well suited to retain radionulcides and/or bind them to their surfaces. This process is called adsorption.
  • A few radionuclides, as, for example, Iodine-129 are not adsorbed, but slowly travel through Oplainus Clay. The primary transport process is molecular diffusion, which is based on reaching an equilibrium concentration.
  • Opalinus Clay also has the property of self-sealing, by which artificially opened fractures or reactivated existing fault surfaces are automatically closed up again by saturation of the rock due to the swelling capacity of certain clay minerals.

 

The disadvantages of Oplinus Clay for deep geological storage are:

  • An excessively high heat input can alter the structure of Opalinus Clay in such a way that the retention properties are impaired. Countermeasure: The deep repository must be designed in such a way that the Opalinus Clay in the repository is never heated to more than 90 degrees Celsius.
  • A deep geological repository is a challenge for civil engineers, especially to ensure stability for long storage periods. In addition, safeguarding is cost-intensive. Countermeasures: short storage times, construction at lower depths (e.g., 400m~ instead of 900m).

Selection of properties of the clayey and sandy facies of Opalinus Clay: petrophysical (brown), hydraulic (blue), rock mechanic (gray), thermal (red), pore-water (yellow), adsorption (green), and gas (white).

Petrophysical properties of Opalinus Clay. For further information please see the following text