By Ayesha Rascoe and Roberta Rampton
WASHINGTON (Reuters) - U.S. lawmakers, expressing concern and frustration with events unfolding at Japan's stricken Fukushima nuclear plant, pressed nuclear regulators on what steps the United States was taking to prevent a similar disaster at the country's aging fleet of reactors.
The Senate hearing comes as the United States assesses the future role of nuclear power as it tries to address fears from Americans more than two weeks after an earthquake and a tsunami severely damaged Japan's Fukushima nuclear complex.
"I think we're all frustrated with the various kinds of information that's often contradictory coming out of Japan," said Senator Mark Udall, a Democrat from Colorado.
Regulators need to make sure a similar disaster could not happen on U.S. soil, and address "a sense that this is out of control, that the improbable has actually become the possible," Udall told a hearing that spilled into an overflow room.
"SLOW RECOVERY" STARTING
Senators heard some optimistic news from top nuclear officials.
The plant seems to be in the early stages of recovery, Peter Lyons, the head of the Energy Department's Office of Nuclear Energy said.
"However, long-term cooling of the reactors and the pools is essential during this period, and has not been adequately restored to date, to the best of my knowledge," Lyons told lawmakers.
To assist in Japan's efforts to regain control of the plant, the Energy Department is preparing to send radiation detecting robots to the tsunami-stricken nation, Lyons said.
The robots, which were requested by Japan, could provide some information about the plant's nuclear cores and spent fuel pools.
With the full impact of the nuclear crisis not yet known, senators at the hearing pressed the operations manager of the U.S. nuclear safety regulator about whether changes need to be made for U.S. plants.
Bill Borchardt of the Nuclear Regulatory Commission said it's too soon to draw any conclusions, but said the regulator would take any immediate steps it deems necessary to boost safety, and not wait until plants go through the relicensing process.
"If we believe there's a design change necessary that we think needs to be imposed ... we won't wait" for licensing process, Borchardt told reporters after the hearing.
The commission has begun a comprehensive safety review of the nation's 104 nuclear plants in response to the Japanese disaster.
One topic for scrutiny will be whether U.S. plants have enough backup power to keep reactors and fuel pools cool during power failures, Borchardt said.
"I think the question of how long they need to be operable is a very good question," Borchardt told reporters.
Lawmakers also expressed particular concern about the way used radioactive fuel was stored at the nation's nuclear plants. Some U.S. plants utilize the same design as the Fukushima complex, where overheating spent fuel pools have complicated the recovery efforts.
"It seems like this is a design flaw. I'm surprised we haven't addressed it previously," Udall said.
Borchardt assured Udall that the spent fuel issue would be addressed during the commission safety review.
(Reporting by Ayesha Rascoe and Roberta Rampton; Editing by Lisa Shumaker)