Technischer Bericht NTB 85-61

Inventar chemisch-toxischer Stoffe in nuklearen Endlagern und ihre Freisatzung in die Umwelt

According to the protection objectives for Project Gewähr 1985 as formulated by the Federal authorities, a radioactive waste repository should have no adverse effects on man and the environment from a chemico-toxic point of view. This report explains that construction and operation of repositories as described in Project Gewähr 1985 allow this objective to be realised.

The Federal Office for Environmental Protection has made available a list of relevant ecotoxic materials and other substances which could present a problem due to their chemical and toxic properties. The drawing up of an inventory of ecotoxic and other problem substances in the type B and type C repositories (based on the waste sort handbook and supplementary inquiries directed to waste producers) has shown that these materials occur mainly in the type B repository and the heavy metals nickel, cadmium, copper and chrome can be taken as representative.

In agreement with the Federal Office for Environmental Protection, cadmium was selected for further investigation, mainly because of the interest attracted by this metal in ecological discussions. Under the assumption that the cadmium originally emplaced as a metal later oxidises and migrates with groundwater from the repository zone into the biosphere as a bivalent cation, the maximum expected cadmium concentration in the biosphere can be determined. The methods and parameters used for the transport calculation were similar to those for radioactive materials in Project Gewähr 1985.

The maximum Cd concentrations in the ground resulting from the calculations were within the range of natural concentrations in agriculturally viable surface soils. The Cd concentrations calculated for groundwater are around an order of magnitude lower than the natural concentrations in open waters.

No maximum allowable concentrations are laid down for chemico-toxic materials in the environment. However, in order to assess the values calculated, reference can be made to the standard values for heavy metal content in agriculturally viable soils as well as to natural concentrations. For cadmium, the calculated content in the ground is around an order of magnitude lower than the corresponding standard value for agriculturally exploited ground, while the soluble proportion is around a factor of 30 lower than the relevant standard value.

Based on the conservative calculation of material transport in the geo- and biosphere and on the evaluation of the results outlined above, it can be concluded that the cadmium present in the repository causes no significant increase in environmental Cd concentrations The ecotoxic risk potential of cadmium from the type B repository can therefore be regarded as insignificant.

Simple comparative calculations show that the ecotoxic conditions for the other heavy metals (nickel, copper and chrome) are basically the same as those for cadmium.