Investigations into an increased immobilizing effect against multivalent cations of the near range of a salt dome repository by means of hydroxyl apatite. Final report

The pilot project was designed to investigate, within a short time frame, the immobilizing effect of hydroxyl apatite under conditions as close as possible to real repositories, and to study the possibility of using hydroxyl apatite as an aggregate to the backfilling material. Investigations centered on the two actinide elements uranium and thorium, the elements neptunium and plutonium being investigated only, for reasons of radiation protection, with regard to their depletion degree and reaction kinetics. All experiments were carried out in three different, repository-relevant brine solutions in keeping with the recommendations given by the HAW working group of the Federal Ministry of Research and Technology (Q-lye, solution II and solution III). Since increased temperatures have to be expected in a repository because of the geothermal temperature gradient, on the one hand, and the heat development of the HAW, on the other, the experiments were performed at 25 C, 75 C and 120 C degrees. (orig./DG)