OPERA network

Context

As part of its monitoring brief, IRSN carries out regular measurements of radioactivity levels in the environment, employing high-performance investigation means for the quantification of trace amounts. This mission is one of the components of the territorial surveillance carried out by IRSN throughout France with the participation of nuclear operators and various associations on a regional and/or local level. It therefore closely complements the information from the automatic warning station network Teleray, which would react instantaneously in the event of high contamination but with a lower level of sensitivity. 

Key issues

Measurements from the OPERA-AIR network are also used in a wide range of research and expert appraisal work on the evolution of radionuclide stocks and flows in the environment. In addition to characterising very low levels (traces), the aim is to understand the mechanisms governing the spatio-temporal distribution and transfers of radionuclides of natural and artificial origin within the atmospheric compartment, as well as interactions between the atmosphere and other environmental compartments. Knowledge of these mechanisms then enables IRSN to design and validate the modelling of radionuclide transfer processes in order to best estimate the impact of an accidental release into the environment and the consequences for the use of the environment and human activities.

Network operation

The atmospheric compartment is observed from around fifty atmospheric dust collection stations in France. These stations are managed by IRSN, which also relies on a network of local institutional and academic partners (Météo-France, universities, etc.) to change the filters and send the samples to IRSN. The radioactivity contained in these filters is analysed by IRSN laboratories located in the Paris region (Orsay and Vésinet). IRSN also has mobile OPERA-AIR high throughput stations, used for one-off studies and assessments. These stations are deployed in particular to reinforce the geographical coverage of fixed stations during radioecological site studies or expert assessments.
 
The stations filter the air continuously over the course of a week. Thanks to the filtration of large volumes of air (up to 150,000 m3 of air per week) and the associated "low-level" metrology, detection limits are less than or equal to 0.1 µBq/m3 of air. Analysis results are generally obtained within two weeks of receiving the filters. The actual analysis time varies between 1 and 4 days. These times can be shortened for specific radiological situations, but this is to the detriment of measurement sensitivity.

Data of a patrimonial nature

The OPERA-AIR network has been used to establish and monitor changes in the levels of the main natural radionuclides (7Be, 210Pb, 22Na, 228Ac, 40K, 234Th) and artificial radionuclides (137Cs, 131I, 60Co, 110mAg, 54Mn, 106Rh) in the atmosphere for over 60 years.

This tool was set up as early as 1959 for the atmospheric domain (aerosols, precipitation). This long period of observation has made it possible to build up the time series that are essential for scientific studies. These studies focus in particular on the variability of the levels observed and the persistence of certain long-lived radionuclides in the air in trace amounts. Thanks to its sensitivity, this system helps to detect low-level releases in France. It can also be used to detect significant releases when these occur far from the national territory (re-emission of radionuclides by fires in the forests around the Chernobyl power station, for example), or as was the case following nuclear accidents (Chernobyl, Fukushima) and previously, during the period of atmospheric nuclear testing.

These stations were used in particular in the days following the Fukushima accident to detect the very first signs of the arrival of lightly contaminated air masses over France. On a routine basis, they are used to characterise the ambient background of certain artificial radionuclides such as 137Cs, as well as any variations in radioactivity levels linked to meteorological conditions or dust levels. OPERA-AIR stations also record meteorological data, in particular wind speed and direction, temperature, humidity and rainfall.

Upgrading of the network

In order to strengthen national coverage, new sites have recently been equipped: Pic du Midi de Bigorre in the Pyrenees, Romans-sur-Isère in the Drome region, Biarritz, and soon Narbonne.