WASHINGTON — The chairman of the United States gave a far bleaker appraisal on Wednesday of the threat posed by ’s nuclear crisis than the Japanese government had offered. He said American officials believed that the damage to at least one crippled reactor was much more serious than Tokyo had acknowledged, and he advised Americans to stay much farther away from the plant than the perimeter established by Japanese authorities.
The announcement opened a new and ominous chapter in the five-day-long effort by Japanese engineers to bring the six side-by-side reactors under control after their cooling systems were knocked out by an earthquake and a tsunami last Friday. It also suggested a serious split between Washington and its closest Asian ally at an especially delicate moment.
The Congressional testimony by Gregory Jaczko, the chairman of the commission, was the first time the Obama administration had given its own assessment of the condition of the plant, apparently mixing information it had received from Japan with data it had collected independently.
Mr. Jaczko’s most startling assertion was that there was now little or no water in the pool storing spent nuclear fuel at the No. 4 reactor of the Fukushima Daiichi Nuclear Power Station, leaving fuel rods stored there exposed and bleeding radiation into the atmosphere.
As a result, he said, “We believe that radiation levels are extremely high, which could possibly impact the ability to take corrective measures.”
His statement was quickly but not definitively rebutted by officials of Tokyo Electric Power, the Daiichi’s plant’s operator, and Japan’s nuclear regulatory agency.
“We can’t get inside to check, but we’ve been carefully watching the building’s environs, and there has not been any particular problem,” said Hajime Motojuku, a spokesman for Tokyo Electric. Speaking on Thursday morning in Japan, Takumi Koyamada, a spokesman for the regulatory agency, said that when it was checked 12 hours earlier, water remained in the spent fuel pool at reactor No. 4.
“We cannot confirm that there has been a loss in water,” he said.
On Wednesday night, Mr. Jaczko reiterated his earlier statement and added that commission representatives in Tokyo had confirmed that the pool was empty. He said Tokyo Electric and other officials in Japan had confirmed that, and also stressed that high radiation fields were going to make it very difficult to continue having people work at the plant.
If the American analysis is accurate and emergency crews at the plant have been unable to keep the spent fuel at that inoperative reactor properly cooled — it needs to remain covered with water at all times — radiation levels could make it difficult not only to fix the problem at reactor No. 4, but to keep servicing any of the other problem reactors at the plant. In the worst case, experts say, workers could be forced to vacate the plant altogether, and the fuel rods in reactors and spent fuel pools would be left to meltdown, leading to much larger releases of radioactive materials.
While radiation levels at the plant have varied tremendously, Mr. Jaczko said that the peak levels reported there “would be lethal within a fairly short period of time.” He added that another spent fuel pool, at Reactor No. 3, might also be losing water and could soon be in the same condition. Efforts to pour in water by dumping it from helicopters were suspended, for fear that the helicopter crews would receive too large a dose of radiation.
Mr. Jaczko’s testimony came as the American Embassy in Tokyo, on advice from the Nuclear Regulatory Commission, told Americans to evacuate a radius of “approximately 50 miles” from the Fukushima plant.
The advice to Americans in Japan represents a graver assessment of the risk in the immediate vicinity of Daiichi than the warnings made by the Japanese themselves, who have told everyone within 20 kilometers, about 12 miles, to evacuate, and those 20 to 30 kilometers to take shelter. While maps of the plume of radiation being given off by the plant show that an elongated cloud will stretch across the Pacific, American officials said it would be so dissipated by the time it reached the West Coast of the United States that it would not pose a health threat.