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Technischer Bericht NTB 83-09

Untersuchungen zum Sorptionsverhalten von Cs-137 und Sr-90 in verschiedenen Gestein/Lösung-Systemen

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In order to estimate the rate of transport of nuclides in the event of water penetration into an ultimate underground repository for radioactive waste, knowledge of the sorption capability of the surrounding rocks is needed. The sorption behaviour of caesium-137 and strontium-90 on powder samples of generic types of 3 clays, 2 sulphate rocks, 6 crystalline rocks, and 2 fissure minerals in different rock-specific waters has been investigated in batch experiments. The nuclide distribution coefficients determined describe the distribution of the nuclide among the solid and the liquid phase of the batch under conditions which may occur at the rock as well as in the water during migration.

Of the experimental parameters

  • ion strength of the solution
  • temperature
  • initial radioactivity of the solution
  • rock/solution ratio of the batch

the ion strength exerts the greatest influence. In general, the nuclide sorption at the rock decreases with increasing ion strength of the carrier solution.

The sorption of strontium is within the same order of magnitude in comparable waters on all the rocks investigated.

The sorption capability of caesium is, by some orders of magnitude, higher on clays, mylonite and chlorite than that of strontium. The sorption behaviour of caesium on clays and crystalline rocks is somewhat different according to their origin.

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