MeteoSwiss - CN-MET

A meteorological system for nuclear emergency response in Switzerland

MeteoSwiss introduced a new wind analysis and prediction system (CN-MET) for nuclear emergency response in Switzerland and its immediate surroundings in late 2009. A special measurement network captures the current wind and other weather parameters up to a height of several kilometres. The newly developed weather prediction model COSMO-2 delivers, among others, highly resolved wind and precipitation fields for the simulation of the dispersion of radioactive clouds. The novel combination of measurements and model predictions provides important information for the Federal Nuclear Safety Inspectorate ENSI and the National Emergency Operations Centre NEOC for the assessment of an emergency situation in Switzerland.

The Federal Office for Meteorology and Climatology MeteoSwiss, in close collaboration with the Federal Nuclear Safety Inspectorate ENSI, developed the new wind analysis and prediction system CN-MET (Centrale Nucléaire et METéorologie) during the years 2005 to 2009 and put it in operations in late 2009. A number of specialized measurement devices are part of this system, as well as the newly developed weather prediction model COSMO-2. The combination of precise measurements and highly resolved model predictions allows to determine wind fields and weather development in the vicinity of the nuclear power plants in Switzerland and the surrounding countries, and to forecast the dispersion of contaminated air masses. Both the ENSI as well as the National Emergency Operations Centre NEOC use this information for their assessment of emergency situations. This information in the end helps the NEOC to take emergency response measures for civil protection.

Figure 1: Wind profiler (left) and radiometer (right) continuously measure wind, temperature and humidity up to several kilometres height at the sites Schaffhausen, Payerne, and Grenchen. The wind profilers are based on the same measurement principle as weather radars, but point straight up and are sensitive to clear air reflections.

Special measurement devices for nuclear emergencies
MeteoSwiss installed a specialized network (Figure 2) for the CN-MET system. It measures in detail the atmosphere above the Swiss Middleland and the vicinity of the Swiss nuclear power plants. At the sites of Schaffhausen, Payerne and Grenchen, the remote sensing instruments - wind profiler (Figure 1) and temperature radiometer - continuously measure wind, temperature and humidity from the ground up to several kilometres height. The wind profilers work with the same measurement principle as weather radars but are pointing straight up. Temperature radiometers deduce the temperature from the infrared radiation of the atmosphere. High telecommunication towers are located on the Uetliberg, Saint Chrischona, Bantiger and Stockeren mountains, carrying meteorological measurement devices on 100 m to 250 m height above ground. The measurements in the free atmosphere are essential to exactly capture the movement of an eventual radioactive cloud and to predict its dispersion. At the locations of the nuclear power plants, MeteoSwiss measures turbulence in addition to the conventional meteorological parameters. This special measurement network is completed by the MeteoSwiss ground based network called SwissMetNet, which collects the meteorological parameters near the ground nationwide.

Figure 2: The CN-MET Network of MeteoSwiss. Green: remote sensing instruments; blue: sites of the nuclear power plants with SwissMetNet stations and turbulence measurements; red: telecommunication towers with meteorological measurements.

The numerical weather prediction model COSMO-2 for dispersion calculation
The measurements of the three wind profilers and the SwissMetNet are fed into the local weather prediction model COSMO-2 of MeteoSwiss, which was among others especially developed for nuclear emergency situations. Every three hours, the model calculates the weather development over the Alpine region for the following 24 hours on a mesh with 2.2 km horizontal grid spacing. During a nuclear emergency, MeteoSwiss on request by ENSI additionally calculates a model prediction every single hour for the following 6 hours. In such a case, MeteoSwiss gets the highest priority on the super computers of the Swiss National Supercomputing Centre of the ETH Zurich for the calculation of the model forecast. The highly resolved wind and precipitation predictions are sent immediately to ENSI, and the dispersion calculations are sent to the NEOC. In parallel, the MeteoSwiss forecasters provide advice to both institutions during the nuclear emergency about the current weather situation and the future development, based on measurements and dispersion forecasts.

Figure 3: Based on the highly resolved wind fields, the dispersion of contaminated air masses can be predicted.

NADAM - a measurement network for automated dose alerting and measurement
In addition to the new CN-MET system, MeteoSwiss operates the NADAM measurement network on behalf of the National Emergency Operation Centre (NEOC, German name NAZ). More than 60 SwissMetNet stations are equipped with special devices which measure the ambient dose rate. These data are transmitted every 10 minutes to NEOC, together with precipitation, local snow heights and further meteorological measurements. The exceedance of a certain threshold (1 micro-Sv/h) automatically triggers an alarm at NEOC.

Graphical representation of the current daily mean values:
https://www.naz.ch/en/aktuell/tagesmittelwerte.shtml