Status of 236U analyses at ETH Zurich and the distribution of 236U and 129I in the North Sea in 2009

Compact, low energy accelerator mass spectrometry (AMS) has evolved over the past years as one of the most sensitive, selective, and robust techniques for the analysis of heavy and long lived radionuclides. In this study, we will first focus on the analytical capabilities of the compact AMS system TANDY, mainly for 236U analyses, and then present a new dual tracer approach, that combines 129I and 236U. The measured 129I/236U ratios of samples collected in the North Sea in 2009 are in reasonable agreement with the expectations from documented or estimated releases from the two major nuclear reprocessing plants located at Sellafield (GB) and La Hague (F), suggesting that the 129I/236U ratio can be used as a water mass tag in the North Atlantic region. However, our results indicate that, in contrast to 129I, additional contributions of bomb produced 236U cannot be neglected in the North Sea region. This complicates the simple and straight forward use of the 129I/236U ratio as a quantitative tool for the calculation of transport times of North Sea water in the Arctic Ocean.