[en] The 66th PTB seminar was held on April 24th and 25th, 1986, at the Munich Technical University (TUM) in Garching in cooperation with the Institute for Radiochemistry of the Munich Technical University, the 'Nuclear Chemistry' special group of the Society of German Chemists, and UB/SN responsible for the BMFT project. The seminar was organized by the TUM's Institute for Radiochemistry. The seminar dealt with the following main topics: primary geochemical reactions and colloid formation; sorption mechamisms and migration behaviour in Konrad/Gorleben aquifer systems; sampling and experimental investigations; evaluation and interpretation of the data obtained by experiments. The seminar was to achieve the following objectives: information and exchange of experience with regard to the work carried out up to the present; if necessary, formulation of new issues to be discussed; improvement of the interdisciplinary cooperation (chemistry, geosciences, modelling). The following topics and individual aspects were of particular interest and were given special attention: complementary basic research in order to interpret, support and model the results obtained by experiments (sorption mechanisms and thermodynamic data for natural systems); comparability of batch, column and diffusion tests; transferability of laboratory data to natural systems (e.g. Gorleben, Konrad); redox transitions for Np, Tc at Eh values of the natural systems; dependence of the sorption/desorption data on different influencing factors, importance of the influencing factors and selection of data for model calculations. Subject analyses of the individual contributions have been made for the Energy data base. (orig./RB)

[en] The shaking experiments for determination of sorption data of technetium have been made with ten authentic samples of the unconsolidated rock and groundwaters from overlying rock of the Gorleben salt dome (well depths between 3 and 244 m). The sorption data have been taken after a period of seven days up to three months. As the sorption behaviour of Tc very much depends on the oxidation number, the experiments have been carried out under both aerobic and anaerobic conditions (the latter in an inert gas box, argon + 1% CO₂). Further, the effects of EDTA, N-alkylbenzyl sulphonic acid, pyrite, magnetite, CdS, and FeS have been examined. The pH-value and the V/m ratio have been varied. The R_S-values for aerobic conditions have been measured to be between 0 and 0.40 ml/g. Extraction with tetraphenylarsonium chloride revealed TcO₄^-. Addition of FeS strongly augmented the R_S-value. All other conditioning means showed no effect. Under anaerobic conditions, a reduction of Tc(VII) to Tc(IV) has been observed. R_S-values of all samples have been > 100 ml/g. Addition of N-alkylbenzyl sulphonic acid reduced this value. Variation of pH and V/m ratio showed no effect. (orig.)

[en] The sorption study with neptunium has been made in circulation columns packed with unconsolidated rock and groundwaters from the natural environment of the Gorleben salt dome. The groundwaters have been brought to equilibrium state by means of high-annealed NpO₂ and have then be fed under aerobic and anaerobic conditions into the circulation columns packed with natural samples of the unconsolidated rock. The columns and the experiments are described. In the anaerobic experiments the neptunium is present as Np(V). Equilibrium status has been obtained after 60 days. The measured sorption values R_S are between 1 and 20 ml/g, and the R_S-value corresponds to the determined R_D-value. In the anaerobic experiments in an inert gas box (99% argon + 1% CO₂ + 200-500 ppm O₂) neptunium has been present as Np(V) and Np(IV). With loose rock obtained from greater depths the R_S-values are > 100 ml/g, and equilibrium status has not been reached after 60 days. After ultrafiltration of the groundwater in the presence of Np(IV) a clear decrease of concentration has been observed. (orig./RB)

[en] Results of diffusion measurements are reported, obtained with aqueous solutions of U-233, Ra-226, Ni-63, and Se-75 in contact with solid rock samples of the Konrad mine overlying rock. The subsequent derivation of K_d-values and the method applied are explained. (orig.)

[en] Within the framework of siting exploratory work in the Asse salt mine, five deep holes have been brought down, a series of hydrogeological wells (up to a depth of 300 m), and some gauge wells (up to 110 m). Most of the borings are core drills with a diameter of 100 mm. In addition to the usual experiments for rock property determination, samples for the determination of sorption properties have been taken. In order to reduce the effect of the O₂ in the air on the rocks during storage, the bore kernels have been put into O₂-tight casks immediately after sampling and cleaning. Processing has been done by means of a jawbreaker, hammer milling, and a shaking device, all equipped with argon-conditioned boxes. The specimens have been shipped in Al-coated and Ar-conditioned polyethylene containers. (orig.)

[en] In the course of solubility studies with Am(III) and Pu(IV) hydroxide in the presence of high chloride concentrations, a radiolytically induced oxidation of Am(V) and Pu(VI) has been observed by spectrophotometrical measurements. This oxidation process has been seen to be dependent on the specific α-activity in the solution, as well as on the pH-value and the chloride concentration. During the experiments, a considerable increase in the redox potential to values of over +1000 mV could be measured. The results are interpreted to reveal a radiolytic formation of oxidizing chlorine species, and their reaction with the actinide ions present in the solution. A reaction pattern is presented for the radiolysis of concentrated chloride solutions which describes all the phenomena observed. This pattern and the Eh-pH-diagrams of Np, Pu and Am are used as a basis for discussing the redox behaviour of actinides in salt solution. (orig.)

[en] The diffusion experiments made in accordance with the examples given by Swedish experts or by Bradbury/Crank require the initial activity in the active feed reservoir to be constant over the entire experiment. As this condition frequently can be fulfilled only approximatively, the diffusion coefficients are calculated by means of Fick's second law, taking into account concentration changes in the two reservoirs. This evaluation method is explained for some experiments with solid rock samples from the natural environment of the Konrad ore mine, and is compared with the method applied by Bradbury/Crank. (orig.)

[en] The knowledge of cation-humic matter interactions has a great importance in order to have a better understanding of the contribution of these substances to the possible transport of radioactive elements in the geosphere via groundwaters. The method chosen to study the formation of soluble species between lanthanides/actinides ions and humic acids from different origins is a chromatographic technique of gel filtration. This dynamic equilibrium method is based on the separation of the formed complex and the free cation by the porous packing gel. Different elements have been studied by this method: UO₂²⁺, Eu³⁺, Th⁴⁺ and global interaction constants have been calculated. The application to transuranic elements is undertaken. (orig.)

[en] The various techniques are discussed of the sampling of rock or groundwater specimens from the geological environment of a repository for radioactive waste (Gorleben, Konrad shaft). The paper explains the sampling campaign made within the frame of the 'Hydrogeological drilling programme Gorleben (Gohy)' and summarizes the results and experience, leading to an outline of improvements that can be made in order to obtain better information on the radionuclide migration. (RB)

[en] LPAS is explained as the novel, very sensitive spectroscopical method allowing speciation of actinides in natural aquatic systems. The information yield of LPAS corresponds to that of the conventional absorption spectroscopy; but its sensitivity is better by 2 to 3 orders of magnitude, so that for example 2x10^-8 mol/L Am³⁺ could be measured. Principles and method of LPAS are described, and its application to the investigation of the hydrolysis reaction of Am³⁺ and the behaviour of Am³⁺ in various types of groundwater. (orig.)