As soon as abnormal traces of radioactivity are detected in the air anywhere in Europe, an informal network of experts from public bodies such as IRSN springs into action to locate their origin and evaluate the risks to the population.
On March 18, 2015, a radioactivity monitoring station belonging to the Swedish Defense Research Agency (FOI) detected unusual traces of iodine-131 in the Stockholm region. The concentration did not present any risk to the population, but raised certain questions. Where was this pollution coming from? Did it concern other countries? Would it increase? To find out, the head of the Swedish station contacted European colleagues, fellow members of the informal network Ring of Five (Ro5).
IRSN then contributed its expertise to reconstruct the air mass trajectories. “The iodine-131 detected in Sweden, then Finland, came from the east,” explains Olivier Masson, an IRSN specialist in atmospheric monitoring. “The area concerned, which extended from Poland to Lithuania and across the whole of Scandinavia, indicated a distant source, in all likelihood somewhere in Russia. Using the Institute’s very high-volume filtration stations and gamma spectrometers, we detected micro-traces in France of less than 0.8 micro-becquerels per cubic meter (µBq/m3).”
IRSN's OPERA-Air network aerosol sampling station in La Seyne-sur-Mer
Reconstructing the trajectory of pollution
The origins of the Ro5 go back to 1983, when scientists from northern Europe would occasionally detect recently produced fission or activation products in the air. This was in spite of the fact that atmospheric nuclear testing had come to an end.
Five of these scientists - one German, one Swedish, one Norwegian, one Finnish and one Danish - decided that whenever the smallest trace of radionuclides was detected in a country, all the others should be informed immediately. The only condition for joining this new network was to have stations capable of detecting very low concentrations in the atmosphere, in the order of tenths of a µBq/m3. IRSN and its permanent radioactivity observatory Opera-Air meet this condition.
The Ro5 greatly expanded after the 1986 Chernobyl accident in Ukraine. Today, the network has 110 aerosol collection sites across Europe and almost 90 experts, four of whom are from IRSN. It has managed to maintain its informal nature as per the original aim: it operates based on peer exchange.
“Following an alert, we transfer the data gathered by members onto a map of Europe. We compare our hypotheses using air mass dispersion modeling tools to trace back the path of the releases”, explains Olivier Masson.
The international dimension of the network is vital, particularly when reconstructing the trajectory of pollution. The Ro5 therefore involves around 20 European countries, in addition to contacts in the United States and Canada.
A network activated three to four times a year
The members of the Ro5 highlight its speed, which is down to its informal nature. “Although more formal networks exist, the ‘Ring’ is more reactive”, explains Sybille Estier, a radiation protection specialist at the Swiss Federal Office of Public Health. “This became clear in 2011 with the accident at the Fukushima nuclear plant in Japan.”
Numerous European laboratories had “seen” the plume of iodine-131 and cesium-134, and immediately made their data available. “In just a few days, we were able to access a large number of measurements”, notes Damien Didier, an IRSN expert in the atmospheric dispersion of radionuclides.
Olivier Masson continues: “We collected these data into a document that provides a timeline of the event. Although the impact was minimal in Europe,
our publication has become a benchmark. It is the second most-cited work on the accident.”
With the improvement of measuring instruments, such as those introduced at IRSN by the Environmental Radioactivity Measurements Laboratory, the network is being mobilized more often. The network is now activated around three to four times a year.
Certain radioelements should trigger an alert
The aim of the Ro5 is to understand where pollution comes from. The detection of iodine-131, for example, can only be due to a relatively recent release, as it is very short-lived. Cesium-134 has a radioactive half-life of two years, and tends to fall to the ground. If it appears, it means that a new accident has occurred in a plant. As for radioactive xenon, this may indicate nuclear weapons testing.
When the network is active, the experts also work to assess the health risks. Damien Didier calculates the doses received by populations or French nationals present in the area where the highest concentrations were measured during detection periods.
From alerts to patents
The Ro5 has never had to deal with an emergency health situation. However, the experience acquired by the network has made it possible to advance atmospheric monitoring techniques.
In August 2008, in Belgium, the Fleurus Institute for Radioelements, which manufactures isotopes for medical use, observed an abnormal release of iodine-131. Although the incident did not present any risks to the population or environment, it led to improvements in gaseous iodine filters, according to Olivier Masson.
At Fleurus, the French gaseous iodine filters failed to detect anything, even though iodine-131 was being found in vegetation just over the Belgian border. “Several hypotheses were produced, including that the rain could have saturated the filters with moisture. In March 2014, IRSN filed a patent for a device to reduce the impact of moisture on the samples taken at its stations.”
