President Barack Obama said Thursday he had asked nuclear regulators for a comprehensive review of the safety of U.S. plants in light of the disaster in Japan, saying, "Nuclear energy is an important part of our own energy future."
Obama said he made the request to the Nuclear Regulatory Commission. He spoke after the commission's head said that it could take weeks to bring the crippled nuclear complex in northeastern Japan under control.
In brief remarks at the White House after a trip to the Japanese Embassy to express his condolences, Obama also sought to assure Americans that the disaster currently posed no threat to the United States.
"We do not expect harmful levels of radiation to reach the West Coast, Hawaii, Alaska or the U.S. territories in the Pacific," Obama said, repeating the remark for emphasis.
Obama said that the United States "has a responsibility to learn from these events."
The president also defended the recommendation of federal nuclear safety officials of a 50-mile evacuation zone around the crippled nuclear power plan for American troops and citizens in Japan, even though it's far larger than the zone spelled out by Japanese officials.
"This decision was based on a careful scientific evaluation," Obama said. "Beyond this 50-mile radius, the risks do not currently call for an evacuation."
Japanese officials have established a 12-mile evacuation zone and have said that people living between 12 and 20 miles from the plant should stay inside.
"We have seen an earthquake and tsunami render an unimaginable toll of death and destruction on one of our closest friends and allies in the world," said Obama. "And we've seen this powerful natural disaster cause even more catastrophe through its impact on nuclear reactors that bring peaceful energy to the people of Japan."
In earlier developments, low concentrations of radioactive particles were heading eastward from Japan's disaster-hit nuclear power plant and were expected to reach North America in days, a Swedish official said Thursday.
Lars-Erik De Geer, research director at the Swedish Defense Research Institute, a government agency, was citing data from a network of international monitoring stations established to detect signs of any nuclear weapons tests.
Stressing that the levels were not dangerous for people, he predicted the particles would continue across the Atlantic and eventually also reach Europe.
"It is not something you see normally," he said by phone from Stockholm. But, "it is not high from any danger point of view."
He said he was convinced it would eventually be detected over the whole northern hemisphere.
"It is only a question of very, very low activities so it is nothing for people to worry about," De Geer said.
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"In the past when they had nuclear weapons tests in China ... then there were similar clouds all the time without anybody caring about it at all," he said.
Before he spoke, the U.S. Nuclear Regulatory Commission advised any Americans living near Japan's crippled Fukushima nuclear plant to move at least 50 miles away but it played down the risks of contamination to the United States.
"All the available information continues to indicate Hawaii, Alaska, the U.S. Territories and the U.S. West Coast are not expected to experience any harmful levels of radioactivity," it said in a statement on Wednesday.
De Geer was commenting on data from the Comprehensive Test Ban Treaty Organization (CTBTO), a Vienna-based independent body for monitoring possible breaches of the test ban.
He said he believed the radioactive particles would "eventually also come here."
The CTBTO has more than 60 stations around the world which can pick up very low levels of radioactive particles such as cesium and iodine isotopes.
It continuously provides data to its member states, including Sweden, but does not make the details public.
The New York Times said a CTBTO forecast of the possible movement of the radioactive plume showed it churning across the Pacific, and touching the Aleutian Islands on Thursday before hitting southern California late on Friday.
It said health and nuclear experts emphasized that radiation would be diluted as it traveled and at worst would have extremely minor health consequences in the United States.
In a similar way, radiation from the Chernobyl disaster in 1986 spread around the globe and reached the west coast of the United States in 10 days, its levels measurable but minuscule, the newspaper said. The CTBTO projection gave no information about actual radiation levels but only showed how a radioactive plume would probably move and disperse, it said.
The Associated Press and Reuters contributed to this report.