By Declan Butler

Nature revealed earlier this week than an international agency set up to detect nuclear tests, the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), is transmitting detailed data on the spectrum of radionuclides and their levels in the air in and around Japan and the Asia-Pacific region to its member states each day, but that the CTBTO could not release these data to the public because it lacked a mandate to do so.

Now, at least one CTBTO member state, Austria, intends to make some of the data public in the form of summary reports and forecasts of global radiation spread.

Nature has also learned that initial CTBTO data suggest that a large meltdown at the Fukushima power plant has not yet occurred, although that assessment may change as more data flow in during the coming days. Lars-Erik De Geer, research director of the Swedish Defence Research Institute in Stockholm, which has access to the CTBTO data and uses it to provide the foreign ministry and other Swedish government departments with analyses, says that the data show high amounts of volatile radioactive isotopes, such as iodine and caesium, as well the noble gas xenon. But so far, the data show no high levels of the less volatile elements such as zirconium and barium that would signal that a large meltdown had taken place -- elements that were released during the 1986 reactor explosion in Chernobyl in the Ukraine.

Rather, the data sit well, he says, with a scenario wherein the main release of radioactivity has come from the release of excess pressure in the containment vessels of affected reactors, and the subsequent explosion of the evacuated hydrogen-laden steam within the reactor buildings. The radioactive plume will spread around the hemisphere within weeks, he predicts, but the levels of radioactivity outside Japan will not be dangerous. The levels in Japan itself, outside the immediate vicinity of the Fukushima power plant, "wouldn't scare me", he adds.

Watchful waiting

De Geer and other scientists are keenly awaiting the fresh data that they will receive from CTBTO over the next few days. Initial data from a station near Tokyo were corrupted because the collection filters used in the sensors were contaminated earlier this week during handling when a plume of radioactivity fanned over the station building, according to Gerhard Wotawa, a researcher at Austria's weather service, the Central Institute for Meteorology and Geodynamics in Vienna. That situation has now been resolved and better data are expected from tomorrow, he says.

The centre this week published maps of radioactive spread based on atmospheric transport models, which incorporate weather forecasts. (See this animation of the predicted course.) Given prevailing winds, plumes of low levels of radiation are expected to travel across the Pacific Ocean and reach the western seaboard of the United States by the end of the week. Stations in Russia are starting to pick up increases in radioactive noble gases, says Wotawa, and stations outside Japan are likely to start detecting higher radionuclides levels in the coming days.

The CTBTO data come from a worldwide network of radionuclide particulate monitoring stations operated by the Preparatory Commission of the CTBTO, a Vienna-based body set up to build a verification regime for a global ban on the testing of nuclear weapons, so that this network will be operational when enough of the organization's member states have ratified the treaty for it to enter force. The organization monitors radionuclide, seismic, hydroacoustic and infrasound characteristics at stations across the globe to check for the tell-tale signals of a nuclear bomb test.

The CTBTO has 60 radionuclide particulate monitoring stations in operation, and two of these are in Japan, near Tokyo, with dozens of others, often on islands, throughout the Asia-Pacific region (see map). It also has instruments to monitor noble gases, such as xenon. These stations monitor the air continuously, and so have extensive data on any radionuclides projected into the atmosphere during the ongoing nuclear disaster.

The data would be of enormous public interest as they would provide a far fuller picture of the extent and spread of any current or future radioactive release from the major Japanese nuclear accident now under way. But although the data are being made available to member states and their radiation protection services, the CTBTO cannot make them public.

Worldwide web

The CTBTO does make available its hydroacoustic and seismic data -- among the most reliable and rapid around -- for the purposes of tsunami warnings, and indeed these data contributed to the rapid alerts issued by tsunami warning systems following the 9.0-magnitude earthquake. The agency's member states agreed to this after the 2004 Indian Ocean tsunami. But the CTBTO has no mandate for making radionuclide data publicly available for the purposes of monitoring nuclear accidents, because its member states have not yet agreed for it to have this role -- although it does have a mandate to release radionuclide data on nuclear tests (see, for example, 'North Korea's ignoble blast').

Yet its radionuclide network is also well adapted to monitoring levels of radiation in the fallout from nuclear accidents -- it is still picking up radioactive caesium-137 (which has a 30-year half-life) from the 1986 Chernobyl reactor explosion in the Ukraine, for example -- and its website lists such work as one of the civil benefits of its network of monitoring stations.

Each particulate monitoring station sends one -ray spectrum per day, a two-dimensional plot showing which radionuclides, and how much of each, occur in its sampling. Nuclear accidents produce a spectrum of radioactive fission products, including various radioisotopes of iodine, caesium and zirconium. The network can pick up all of them, says Lassina Zerbo, director of the CTBTO Preparatory Commission's International Data Centre Division in Vienna.

De Geer criticizes the secrecy surrounding CTBTO data. "For me it is absolutely clear: all this should be totally open," he says. "The CTBTO is a complicated organization; certain member states want all data to be classified, so they are not allowed to be given out, " says De Geer, who was formerly head of the CTBTO's Radionuclide Development Unit. Even freeing the tsunami-relevant data "took years of discussion", he says.

He believes that the national laws of Sweden, a CTBTO member state, give it the right legally to "do what we want with the data", adding that the issue of the confidentiality of the data is nonetheless still a "grey zone". Wotawa likewise believes that Austria has the right to use the data, and says that his centre will be publishing CTBTO data in the daily updates of the Fukushima fallout that it is providing on its website.

Zerbo says that the CTBTO's radionuclide monitoring service would be well placed to take on any international role in monitoring nuclear accidents for radiation protection purposes. "Japan and other countries have their own national radiation protection services, but where we could be useful is the worldwide nature of our monitoring network", he says. "We are the only truly worldwide radionuclide monitoring network." In a step towards that role, the CTBTO and the International Atomic Energy Agency in Vienna yesterday agreed to cooperate.