The nuclear crisis in Japan this spring is not over, but it will not come close to rivaling the Chernobyl disaster in Ukraine 25 years ago, said John Boice, a professor at the Vanderbilt University School of Medicine in Tennessee.
Boice, an international authority on radiation effects, was the featured speaker Thursday at the Department of Energy's national Integrated Safety Management Champions Workshop in Kennewick. He had just returned from Japan, where he provided information to the government on radiation health and safety.
On March 11, a magnitude-9 earthquake was followed by a tsunami with a 50-foot-high wave that hit the Fukushima nuclear power plant, causing a full meltdown at three reactors.
As bad as that was, "it was not Chernobyl," Boice said. "The doses to people were much lower."
That was in part because Japan acted quickly to protect its citizens from radiation, he said.
The Chernobyl reactor had no containment dome and it burned for days, releasing far more contamination. The firefighters who responded were true heroes, some of whom gave their lives, Boice said.
More than 130 had acute radiation sickness and 28 died within a few months, he said. Continued medical checks show the firefighters have developed cataracts at high rates, he said.
Over three years, 530,000 workers helped clean up the Chernobyl reactor remains. Their mean radiation dose, or energy deposited in their body by radiation, was 10 rem, although some had far more. Rem is a measure of health effects.
In Japan, no acute effects of radiation have been seen in the firefighters at Fukushima, Boice said.
The 7,800 workers at the reactors as of late spring had an average exposure of 0.8 rem, Boice said. However, 30 had 10 to 25 rem and at least two had more.
The lifetime risk of developing cancer may be 1 to 2 percent for exposure greater than 10 rem, he said.
Since Chernobyl, there has been an epidemic of thyroid cancer. About 7,000 children -- who are most vulnerable to the cancer -- have been diagnosed with thyroid cancer, he said.
They likely were exposed through milk from cows that grazed on grass contaminated with radioactive iodine. Iodine concentrates in the thyroid.
The Soviet government did not warn people not to drink the milk, but the Japanese government did, Boice said. In addition, far less radioactive iodine was released at Fukushima than at Chernobyl.
At Fukushima, "the dose to people appears to be very, very low," he said.
Japan evacuated people in a series of zones as the disaster progressed, while the evacuation at Chernobyl was slow, Boice said.
Fish, vegetables and milk were monitored in Japan to protect consumers.
People who left the area also were monitored and any contamination found was removed by showering, he said. People who had been cleared were given cards to certify their status.
About 1,000 children near Fukushima were monitored for thyroid exposure to radiation and although some levels were detected, they were small, Boice said.
"The population exposure seems minimal at this time," he said.
But the crisis is not over, he said.
Much of the contamination released from the Fukushima reactors blew out to sea, but enough contamination spread inland to require at least 80,000 people to be evacuated from their homes and farms, he said.
Questions remain about when those evacuated will be allowed to return to their homes, if ever, Boice said.
In addition, Japan has 100,000 tons of highly radioactive water stored in tanks after water was poured into the reactors when power was lost, and the reactors are not yet in cold shutdown.
However, the nuclear meltdown is just part of the disaster caused by the earthquake and tsunami, Boice said. The natural disaster killed 16,000 people and 4,000 people remain missing.