Meanwhile, the operator of the crippled Fukushima nuclear power plant reported no significant progress in stopping the leak of radioactive water into the sea. Tokyo Electric Power Co. officials think the leak has been coming from a concrete pit holding power cables near reactor No. 2, and attempted Sunday to seal a crack there with a special polymer.
The government has come under renewed pressure from groups including Greenpeace to expand its evacuation area, but at the same time, residents who vacated the 12-mile zone have been seeking permission to return to their homes briefly to gather personal items. Officials in recent days have not shown signs of budging in either direction, and Edano said Sunday the current order will last "a long time," though he conceded it was "tough on residents."
The chief cabinet secretary added that the government had checked the thyroid function of 900 children up to age 15 in two villages, Iitate and Kawamata, just outside the 18-mile perimeter and none was found to have been exposed to high radiation levels. High levels of radiation have been detected in the water and on grass in Iitate. Edano said it was the third time that the government had conducted tests on children in areas just outside the 18-mile zone.
The official death toll from the March 11 disaster topped 12,000 on Sunday as about 25,000 U.S. and Japanese troops finished an intensive three-day effort to recover bodies. The search located 77 corpses, but more than 15,000 people are still officially listed as missing. Another 160,000 people remain in shelters.
The Red Cross has dispatched more than 200 emergency relief teams to the disaster zone and organized thousands of volunteers to assist victims. But no displaced people have received cash handouts from the pot of 870 billion yen collected by the Japanese Red Cross and Red Crescent Societies and the Central Community Chest of Japan.
In past disasters, independent panels in each prefecture have determined who gets such handouts and how much they get. Edano suggested that this time, the process must be streamlined.
"Normally donations are disbursed through local governments that rely on independent committees to decide on the conditions for dividing up the money," Edano said. "But this time, the central government has a role to play in setting up an independent committee" that will figure out how to split up donations.
Tomohide Atsumi, president of the Nippon Volunteer Network Active in Disaster, said the Red Cross has "a policy of equity and places a high value on equality, and it takes times to assess damages."
In contrast, he said, donations to nonprofit groups often get spent immediately. Atsumi said his organization used funds collected right after the disaster to buy underwear and other supplies for evacuees and charter a bus for volunteers to help victims in northern Japan.
Overall, he said, Japan is still learning how to strike the right balance between order and a more free-form approach in its disaster relief efforts. An overemphasis on organization and top-down decision making, he said, probably prevented more volunteers from going to the disaster zone more quickly and doing some good.
"The drive to be organized is very strong in our society but people are not good at socially improvising," he said. "I like to use the metaphor of classical music vs. jazz. Our traditional disaster response is like classical music -- there's a conductor, a big orchestra, a fancy hall. Disaster relief should be more like jazz -- you can do something with one trumpeter, one drummer. You don't need a whole orchestra."
As the disaster zone has become more accessible, experts are learning more about the size and force of the massive tsunami.
A group of researchers led by Yoshinobu Tsuji of Tokyo University's Earthquake Research Institute has been studying the tsunami-hit area around Miyako, in Iwate prefecture. They found evidence that the waves could have been as high as 124 feet, according to public broadcaster NHK. That would make them the tallest waves to hit Japan's northeastern shore since 1896, when the tsunami waves recorded at Ofunato were 125 feet high.
"This tsunami was comparable to the  tsunami -- and it might have been bigger," Tsuji said.