|Autoren des Beitrags|
|Titel des Beitrags||Vertical distribution of radionuclides in three lakes along the river Aare in Switzerland||Erscheinungsjahr||2014||Publikations-Art||Kongressschrift / Tagungsband||Name der Konferenz/Veranstaltung||International Conference on Radioecology and Environmental Radioactivity|
|Abstract :||During the years 20092013 sediment cores with lengths of about 1 m were taken from Lake Brienz, Lake Thun, and Lake Biel. River Aare coming from glaciers in the Grimsel area is flowing essentially to the north through lakes Brienz and Thun, and then passing the capital Bern. North of Bern the nuclear power plant Mühleberg is located on the banks of River Aare which then passes Lake Biel.
Sediment cores were sliced into 1 cm layers, freeze-dried and homogenized. Gamma-spectroscopy was performed with HPGe-detectors (BEGe-5030 with carbon windows) after sealing the samples into radon-tight aluminium composite foil. Self absorption in the samples and summation corrections in the spectrum were taken into account.
Later on, complete lithium borate fusions of sediment samples were performed and the molten samples were poured into concentrated nitric acid. After the silicates were precipitated, plutonium was separated with Teva-columns. ICP-MS measurements were performed to determine the content of different Pu-isotopes.
In sediments of all three lakes maxima in the 137Cs distributions could be assigned to the maximum of the atmospheric nuclear weapons testing fallout in 1963 which was confirmed by the Pu distributions and by the presence of 241Am. Another peak had to be assigned to the fallout of the Chernobyl nuclear accident in 1986. Confirmation that the top layer had not been lost during sampling is given by the presence of 7Be in those layers.
Dating of sediment layers is also done by 210Pb methods. Here the unsupported 210Pb is received by subtracting the supported 210Pb (determined via 214Pb or 214Bi which are in secular equilibrium with 226Ra) from the total 210Pb.
Pb-dating is in good agreement with Cs-dating and provides a time-dependent sedimentation rate. Single events which led to high sedimentation rates can also be identified by variations of the 40K concentration, bulk density and by variations in the concentration of radionuclides from the 238U-or 232Th-decay series.
The boiling water reactor Mühleberg started operation in 1971. A continuous 60Co discharge from the power plant to the River Aare is revealed by measuring a continuous 60Co activity concentration in the top 20 cm of sediments of Lake Biel although 60Co has a short half-life of only 5.3 years. 60Co was found not only at the deepest position of that basin into which River Aare flows but also in other basins of Lake Biel. Whether additional 137Cs was discharged by the reactor during that period will be clarified by the analysis of Pu isotopic ratios.
Masterstudiengang Umwelt- und Verfahrenstechnik
Fakultät Technologie und Management
Institut für Angewandte Forschung (IAF)
Schwerpunkt Energie und Umwelt (IAF)
Bachelorstudiengang Energie- und Umwelttechnik
Dr. rer. nat.
Radioökologische Studien und Untersuchungen