Technischer Bericht NTB 91-26

Urangehalte von Oberflächen-, Quell- und Grundwässern der Schweiz

This report presents the results of U-analyses in surface and groundwaters in Switzerland, which where carried out in several phases between 1978 and 1986.

Most of the water samples originate from the alpine region and unusually high U­contents were found mainly in regions with known U-mineralisations. The recharge zone of the Rhone valley is of particular interest in this respect and thus formed the focal point of the investigation programme. Some anomalies were also found in the Upper Rhine valley, but practically none in the recharge zones of the Reuss, the Aare and the Ticino.

A wide range of U-contents, between 0.2 and > 100 ppb, was found in groundwaters from alpine granitic complexes. Normal U-contents of around 0.5 ppb were measured in the few surface waters investigated in the regions of the Molasse Basin and Northern Switzerland. According to Nagra's regional hydrology programme, several deep groundwaters in Northern Switzerland and the adjoining region of the Black Forest also show enhanced U-contents (> 2 ppb) and these are included in this compilation.

In general, the interpretation of U-contents remains problematic since the processes and parameters giving rise to these contents are only poorly understood. The results of two extraction experiments, which may lead to a better understanding of the situation, are given.