Meteorology for nuclear accidents

MeteoSwiss operates the CN-MET wind analysis and forecasting system for nuclear incidents in Switzerland and neighbouring countries. It comprises a special monitoring network along with the COSMO-1 weather prediction model. This combination of measurements and the COSMO-1 model provides an important basis for the emergency management in Switzerland.

In close cooperation with the Federal Nuclear Safety Inspectorate (ENSI), MeteoSwiss has developed the CN-MET (Centrale Nucléaire et METéorologie) wind analysis and forecasting system, which began operating at the end of 2009. The system includes a large number of special measuring devices as well as the COSMO-1 weather forecasting model. The combination of precise measurements and high-resolution model forecasts makes it possible to determine wind fields and weather developments around nuclear power plants in Switzerlandand in neighbouring countries and to calculate the dispersion of contaminated air masses. Both the ENSI and the National Emergency Operations Centre (NEOC) use the information to assess the current situation. On this basis, the NAZ is able to take measures to protect the population.

Special measuring devices

Bilder eines Windprofilers und eines Temperatur- und Feuchte-Radiometers.
Wind profilers (left) and temperature radiometers (right), which continually measure vertical profiles for wind, temperature and humidity

MeteoSwiss has developed a specific monitoring network for the CN-MET system. It measures the atmospheric properties above the Swiss Plateau in detail, in particular in the direct vicinity of the Swiss nuclear power plants. It comprises three different monitoring systems.

  • At the sites in Schaffhausen, Payerne, and Grenchen, remote sensing instruments – wind profilers and temperature radiometers – continually measure the wind, temperature, and humidity from the ground up to an altitude of several kilometres. The wind profiler is a radar which measures the radial velocities along beams pointing in the vertical and four near-vertical directions. On this basis, the horizontal wind speed for all altitudes up to 8 kilometres above the ground can be calculated. The temperature radiometers derive the temperature from the intensity of the atmosphere's natural microwave radiation.
  • High telecommunications towers stretching 100 to 250 metres above the ground and equipped with meteorological measuring devices are situated on the peaks of the Üetliberg, St. Chrischona, Bantiger, and Stockeren.
  • At the nuclear power plant sites, MeteoSwiss also measures turbulence in addition to the usual parameters.

This special monitoring network is supplemented by the ground-level monitoring network of MeteoSwiss SwissMetNet, which comprehensively records the meteorological parameters close to the ground.

Dispersion calculations with the COSMO-1 forecasting model

The measurements from the three wind profilers and the SwissMetNet stations are fed into the COSMO-1 local weather prediction model of MeteoSwiss, which was developed to be used in the event of nuclear accidents and for general weather forecasting purposes. Every three hours, the model calculates the weather development in the Alpine region for the coming 33 hours, on a grid with a horizontal grid box size of 1.1 kilometres.

Karte der Nordwestschweiz mit Windpfeilen und Farbflächen für die Windgeschwindigkeit.
Wind map for north-western Switzerland. The dispersion of contaminated air masses can be forecast on the basis of high-resolution wind fields.

The high-resolution wind and precipitation fields of COSMO-1 ultimately enable the forecasting of the dispersion of contaminated air masses as well as the wash-out and deposition of radioactive substances. MeteoSwiss provides  forecasts for wind and precipitation as well as other meteorological parameters without delay to the Federal Nuclear Safety Inspectorate (ENSI), and dispersion calculations to the National Emergency Operations Centre (NAZ). In parallel to this and working on the basis of the relevant measurements and dispersion calculations, the MeteoSwiss meteorologists are responsible for providing both institutions with advice regarding the current weather situation and the future meteorological development in the event of a nuclear accident.

NADAM: Automatic Dose Alarm and Monitoring Network

In addition to the CN-MET system, MeteoSwiss also operates the NADAM monitoring network on behalf of the National Emergency Operations Centre (NAZ). More than 60 automated meteorological stations are equipped with special sensors which measure the level of radioactive radiation (local dose rate). Together with the precipitation data, the local snow depths and other meteorological parameters, MeteoSwiss transmits the NADAM data to the NAZ every ten minutes. If a specific threshold is exceeded (1 micro-Sv/h), an automatic alarm is triggered at the NAZ.

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