Search for long-term radiation trends in the environs of Swiss nuclear power plants

Annually since 1989, biannually since 1994 the sites of the Swiss nuclear facilities are surveyed flying the same survey lines by airborne gamma ray spectrometry. The equipment and the data processing software used for those surveys were built and developed at the Institute of Geophysics, ETH Zurich. For mapping the ground radiation around the nuclear facilities, a pixel representation and a modified spectrum dose index (SDI) method are used. In the search for long-term trends, the local dose rates are calculated first and in turn the net dose rates. So far, no change in the radiation levels was detected over the last 13 years outside of the fenced sites of the nuclear facilities and, especially, no artificial radioactivity was present that could not be explained by nuclear weapon tests or by the Chernobyl event