March 13, 2011 -- Evacuees from the 13-mile-radius danger zone surrounding Japan's Fukushima nuclear plant are being screened for radiation.
Japanese health authorities confirmed that at least 22 people have been exposed to radiation following the hydrogen explosion at the plant's No. 1 reactor building early Saturday morning. Up to 160 more are suspected to have been exposed while waiting for evacuation in the nearby town of Futabe, according to Ryo Miyake, a spokesman from Japan's nuclear agency.
A cooling system malfunction at the plant's No. 3 reactor last night could lead to a similar explosion, but Yukio Edano, the nation's Chief Cabinet Secretary, said, "If there is an explosion, however, there would be no significant impact on human health," according to The Associated Press.
Workers wearing masks and protective clothing are using handheld scanners to measure radiation on the nearly 180,000 people who have fled the 450-square mile zone.
Officials have set up evacuation centers bordering the zone and are working to establish decontamination facilities.
Depending on the level of contamination, evacuees are being advised to dispose of clothing and shower.
"They're doing the same thing we would be doing," said ABC News chief medical editor Dr. Richard Besser. "They'll be monitoring them to see if they have radiation on them. They can decontaminate them."
Potassium iodide pills can help guard against thyroid cancer, Besser said.
Iodine is taken up by the thyroid -- a butterfly-shaped gland in the neck that produces hormones that regulate metabolism. Radioactive iodine in environment after a nuclear accident can cause thyroid cancer. But potassium iodide can block the radioactive iodine from entering the gland.
"One of the things after Chernobyl, you saw massive numbers of cancers in children. The radioactive iodine got into the grass, the cows ate the grass, it got into the milk," Besser said. "If there is a big fallout, they'll tell people not to drink milk or eat food from that area."
Children and pregnant women are most at risk, Besser said.
Japan's Nuclear Fears: No Meltdown Yet
Although the steel container protecting the plant's No.1 reactor was not damaged in the explosion, radiation levels near the plant rose to roughly twice that which constitute an emergency situation, according to Japanese officials. This prompted a doubling of the evacuation radius from the initial six miles.
Radiation levels outside the plant rose again after the malfunction in the No. 3 reactor Saturday night, but soon began to fall, according to Edano.
The explosion in the No. 1 reactor occurred when a build-up of steam was released in an effort to safely decrease pressure. A similar controlled release is planned for No. 3.
"We don't call this situation meltdown," government spokesman, Nori Shikata told "This Week" anchor Christiane Amanpour Sunday morning. "This is a regulated controlled situation. The release of minute radioactive material is based on our efforts to take pre-cautionary methods."
"Whether or not there will be further leaks, the people will be away from danger," Besser said.
Jacky Williams, director and core leader of the Center for Biophysical Assessment and Risk Management Following Irradiation at the University of Rochester Medical Center, called the 12-mile evacuation radius an "extremely conservative safety zone to protect against fallout."
The radiation dose following the Hiroshima and Nagasaki bombings was cut in half every 200 meters from ground zero, Williams said.
But the fallout from a Fukushima could vary greatly depending on the nature of any leak -- whether it's through an explosion of the core, as in Chernobyl, or a slow, controlled release of pressure-building gases. It also depends on the wind.
"Members of the public are not in imminent danger at a distance of 20 kilometers, so long as they are not downwind," Williams said.
The plume from the Chernobyl explosion drifted over large parts of Europe and the Soviet Union, prompting the evacuation of more than 300,000 people.
The scene dredges up memories of the Three Mile Island accident near Harrisburg, Pa., in 1979.
The partial meltdown at the Three Mile Island Nuclear Generating Station, which ended nuclear power construction in the United States, has never been definitively linked to deaths or cancer. But radiation exposure following the Chernobyl meltdown has been directly implicated in more than 50 deaths and suspected in many more.
Japan's Nuclear Fears: Long Term Health Effects Uncertain
The true extent of the disaster's effects, such as the cancer risk posed by widespread low-level radiation, remains unclear.
"No one has yet conclusively assessed this question 25 years after the Chernobyl Accident," said John Williams, professor of nuclear and energy engineering at the University of Arizona.
The acceptable level of radiation exposure, up to 10 millisieverts per year, is based on a "no threshold" model, which assumes a direct relationship between radiation dose and cancer risk and implies anything beyond natural levels is harmful. But some experts argue that low-level radiation may be less harmful on a per unit basis.
Japanese authorities deny that the exposures reported so far pose any health risks.