Weather information from high up
A weather mast in the vicinity of the Olkiluoto power plant reaches up to a height of one hundred metres and transmits versatile data on the prevailing weather conditions to the control rooms of the plant units and to the Finnish Meteorological Institute. Every three months the data are also reported to the Radiation and Nuclear Safety Authority.
The sensors of the weather mast measure continuously wind speed, direction, scatter of direction and wind stability as well as air temperature. Wind measurements are carried out as three-dimensional ultrasonic measurements. 
The nuclear safety concept is applied also to the measurements i.e. redundant measurements are used. Measurements are also carried out on ground level; air humidity, atmospheric pressure, precipitation and total time of rainfall. The measurement results are recorded in the buffer memory of the central processing unit at the weather station and transmitted from there at intervals of 10 minutes to the plant units, and by a separate transmission to the Meteorological Institute. The Radiation and Nuclear Safety Authority can obtain the data from the Meteorological Institute, if necessary. A radar unit, which monitors vessel traffic in the near area, is also installed on the weather mast as part of TVO’s cooperation with the authorities.
The measurement sensors are installed on the weather mast at heights of 100, 60 and 20 metres, as well as on ground level. The equipment plant of the mast also contains a central processing unit, which comprises a buffer memory. The system is connected to the process computers of the plant units and has a fixed data communication connection also to the Finnish Meteorological Institute. Power supply to the system is arranged from an external 400 kV network and battery backup is also provided.
The central processing unit of the weather mast transmits weather data at intervals of 10 minutes to the control rooms of the plant units. Photo: Hannu Huovila.
Compulsory system under law
The Nuclear Energy Act and the Nuclear Energy Decree as well as the Nuclear Power Plant Guides of the Radiation and Nuclear Safety Authority stipulate that the licensee of the nuclear power plant is responsible for the performance of meteorological measurements in the vicinity of the plant. The weather measurement system is used in the calculation of estimates regarding the dispersion direction and migration of radioactive releases and emissions. Olkiluoto weather mast was erected already in the mid-1970s, when the environmental baseline measurements preceding the operation of the power plant were started.
During normal power plant operation, releases and emissions are insignificant as far as the environment is concerned. In the extremely unlikely case of an accident, the system will produce data on wind direction and speed and the structure of the mixed layer, which make it possible to estimate the dispersion of any radioactive substances.
EU requires that the measurement data of the Meteorological Institute are made publicly available. As a result of this, the data obtained from the weather mast in Olkiluoto are also available through the open data service of the Meteorological Institute.
Radioactive releases and emissions fractions of regulatory limits
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