As radioactive contamination from the Fukushima Dai-ichi nuclear power plant spreads, a global network of sensors is tracking it across oceans and continents. The network was originally set up to detect nuclear weapons testing, but scientists now hope it can tell them more about the accident.
The Comprehensive Test Ban Treaty Organization began setting up its monitoring stations about a decade ago, with the eventual goal of enforcing a worldwide ban on nuclear weapons tests.
"We have currently over 280 sensors worldwide, monitoring underground, the atmosphere, the oceans for any sign of a nuclear explosion, and we're also sniffing the air for any sign of radioactivity," says spokesperson Annika Thunborg.
That now includes radioactivity from the Japanese plant. Explosions at three reactors and a fire at a spent fuel pool have released radiation into the atmosphere.
Gerhard Wotawa, with the Austrian meteorological institute, has been studying data coming in from the monitoring stations and says there's no doubt that what they're picking up comes from Japan.
"Data like that I have never seen in my career," he says, "so it is pretty much clear where it comes from."
The sensors are registering radioactive elements including iodine-131 and cesium-137 — byproducts from nuclear fission inside the core of a reactor. Wotawa has been feeding the data into computer models that can forecast where the radiation will go. He also uses the models to work backward and calculate the amount of material first released. Based on those calculations he says the accident, in some ways, is roughly the size of Chernobyl.
"The daily release is comparable to what was released in Chernobyl," he says. "However, the effect of the power plant accident in Japan is not comparable to the effect of Chernobyl on the former Soviet Union."
That's partially because Chernobyl was inland, and radiation contaminated land in all directions. Fukushima is on the coast, and winds are blowing much of the material out over the Pacific.
Is The Worst Behind Us?
Wotawa's calculations are an estimate, though, and not everyone agrees that the accident is comparable to Chernobyl.
"If I had to guess, I would say the release levels or more like Three Mile Island and less like Chernobyl, but we'll see as time goes forward," says Harry Miley, a nuclear physicist at Pacific Northwest National Laboratory in Washington state. He says analyzing the types and amounts of radioactive material picked up by the sensor network, which will tell researchers around the world more about what happened inside the reactors at Fukushima.
"We might determine things like what was the temperature of the material when the radioactivity was emitted, which material it was," he says. "There are three reactors, and there are spent fuel pools and so forth — they're all potential sources, and we should be able to nail down which source is which."
For now this system may be the only way to measure what's happened — radiation levels on the site are far too high to take a direct look. The sensors should also provide people with a sense of reassurance. Even though radiation from the plant has been picked up across the United States, Miley says that the levels aren't dangerous.
"The highest detection that we've gotten here in the U.S. has been far lower than the natural radioactivity that's already there, so I don't think there's any increased risk to the U.S. public," he says.
And there's more good news — the latest readings here in America seem to indicate that radiation from the plant is decreasing. Miley is hopeful that the worst of the accident may be behind us.