Search for long-term radiation trends in the environs of Swiss nuclear power plants B. Bucher 1 , L. Rybach 2 , G. Schwarz 1 1) Swiss Federal Nuclear Safety Inspectorate, CH-5232 Villigen-HSK, Switzerland 2) Institute of Geophysics ETH Zurich, Schafmattstr. 30, CH-8093 Zurich, Switzerland Abstract 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 was 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 is 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. Keywords: airborne gamma spectrometry, ground radiation, nuclear power plants, local dose rate 1. Introduction There are five nuclear power plants at four sites in Switzerland (Beznau I+II, KKB, PWR; Mühleberg, KKM, BWR; Gösgen, KKG, PWR; Leibstadt, KKL, BWR, see Table 1) with a total generating capacity of 3.22 GWe (production in 2006: 26.2 TWh), supplying 40 % of Swiss electricity production. The Paul Scherrer Institute in Würenlingen, a renowned research facility (PSI), belongs also to the Swiss nuclear installations. Geographically the nuclear facilities are all located in the northern Alpine foreland (see Fig. 1); maps of the environs are displayed in Figures 9-11. Table 1: The Swiss nuclear power plants. Plant Symbol Type MWe Cooling Since Beznau KKB I KKB II PWR PWR 365 365 River River 1969 1971 Muehleberg KKM BWR 355 River 1972 Goesgen KKG PWR 970 Cooling tower 1979 Leibstadt KKL BWR 1165 Cooling tower 1984 The Zwischenlager Würenlingen AG (ZWILAG, interim storage facility for all categories of nuclear waste and spent fuel assemblies, in operation since 2001) is a further nuclear installation, subject to egular surveys.