Some experience with measurements of stack releases and their correlation with environmental measurements

The first nuclear power plants (NPP) in Switzerland were built during the late 1960s and the early 1970s (PWR-Beznau and BWR-Muhleberg). A new generation of NPPs were built ten years later (PWR-Goesgen and BWR-Leibstadt). In all these NPP special attention was given to the sampling and measurements of the releases of radioactive materials, in particular long lived aerosols and J-131. The sampling systems at the Swiss NPP were originally installed on the basis of the American National Standard Guide to sampling Airborne Radioactive Materials in Nuclear Facilities, (ANSI NI3, 1 - 1969) or equivalent standards such as ISO 2889 and DIN 25423. Unfortunately, the sampling systems described in these guides cover only that fraction of radioactive aerosols, which is preferentially retained in various portions of the respiratory tract (0.3 to 10 Μm). In a NPP one can expect during an accident a very wide range of particles with diameters as large as 100 and more Μm, which can be transported away by the stack effluent and may not be properly sampled and measured. It should be taken into account that there are some non filtered rooms and that filters can fail or even break. Such particles when released cause a ground contamination in the vicinity of the plant. Such an event occurred in September 1986 in the NPP-Muhleberg