by the CTBTO - Page 1
- Update 13 April 2011: radioactivity also measured in the southern hemisphere -
Since the double disaster of the 9.0 magnitude earthquake and tsunami that affected hundreds of thousands of people and seriously damaged the Fukushima Daichi power plant in Japan on 11 March 2011, minute traces of radioactive emissions from Fukushima have spread across the entire northern hemisphere. A monitoring network designed to detect signs of nuclear explosions picked up these traces from the stricken power plant.
In all, more than 35 radionuclide stations that are part of the International Monitoring System (IMS) have provided information on the spread of radioactive particles and noble gases from the Fukushima accident. The IMS is a global network that will comprise 337 facilities when complete. Sixty-three of the 80 planned IMS radionuclide stations are already operational and able to detect airborne radioactivity.
The first analysis results of the monitoring data became available a few days after the accident. A clear picture quickly emerged. Initial detections of radioactive materials were made on 12 March 2011 at the Takasaki monitoring station in Japan around 200 km away from the troubled power plant. The dispersion of the radioactive isotopes could then be followed to eastern Russia on 14 March 2011 and to the west coast of the United States two days later.
Spreading across the entire globe
Nine days after the accident, the radioactive cloud had crossed Northern America. Three days later when a station in Iceland picked up radioactive materials, it was clear that the cloud had reached Europe. By day 15, traces from the accident in Fukushima were detectable all across the northern hemisphere. For the first four weeks, the radioactive materials remained confined to the northern hemisphere, with the equator initially acting as a dividing line between the northern and southern air masses. As of 13 April 2011, radioactivity had spread to the southern hemisphere of the Asia-Pacific region and had been detected at stations located for example in Australia, Fiji, Malaysia and Papua New Guinea.
Findings confirm Fukushima release
The CTBTO’s monitoring system, custom-made to detect nuclear explosions, can pick up a range of radioactive isotopes, among them iodine-131 and caesium-137. Looking at the ratios between the various radioactive isotopes – in particular caesium-137 – enables the source of the emission to be identified. In the case of the current readings, findings clearly indicate radionuclide releases from a damaged nuclear power plant, which are consistent with the recent accident at Fukushima in Japan. As of 13 April 2011, the average level of radioactivity picked up by the stations worldwide continued to decline, which is also due to the relatively short half-lives of iodine-131 (8 days) and xenon-133 (5.2 days).
The CTBTO's radionuclide stations are designed to register minuscule amounts of radioactive particles and noble gases – down to a number of a few atoms. The system’s sensitivity is second-to-none - it can detect a concentration of 0.1 g of radioactive xenon evenly distributed within the entire atmosphere of the Earth. A rooftop detector at the CTBTO's headquarters in Vienna still catches traces of emissions from the 1986 Chernobyl disaster.
Benefits for disaster mitigation efforts
The IMS is being built to ensure compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT), which bans all nuclear explosions. CTBTO monitoring data and technologies, however, offer a host of additional benefits, particularly in relation to disaster mitigation. One of these benefits is already in place – the contribution of data to tsunami warning efforts. In 2006, Member States mandated the CTBTO to provide seismic and hydroacoustic monitoring data directly to tsunami warning centres. Data is currently provided to eight tsunami warning centres mainly in the Indo-Pacific region.
Data were also made available to Japan when it was hit by the massive earthquake on 11 March. Tens of thousands of people were tragically killed by the tsunami; still many were saved due to the rapid alerts. According to Japanese authorities, CTBTO data helped them to issue tsunami warnings within a few minutes, thus allowing many people to escape to higher grounds. CTBTO data also helped other countries in the region, such as Australia, Indonesia, Malaysia, the Philippines and the United States, to issue timely tsunami warnings, even though the wave turned out to have lost its devastating power by the time it had reached these countries’ shores.