By Chizu Nomiyama and Shinichi Saoshiro
TOKYO (Reuters) - Japanese engineers were frantically attempting on Saturday to pump out puddles of radioactive water at the earthquake-crippled Fukushima nuclear power plant after it injured three workers and delayed efforts to cool reactors to safe levels.
Underscoring growing international qualms about nuclear power raised by the killer earthquake and tsunami in northeast Japan two weeks ago, U.N. Secretary-General Ban Ki-moon said it was time to reassess the international atomic safety regime.
Radioactive water has been found in buildings of three of the six reactors at the power complex 240 km (150 miles) north of Tokyo. On Thursday, three workers sustained burns at reactor No. 3 after being exposed to radiation levels 10,000 times higher than usually found in a reactor.
"Bailing out accumulated water from the turbine housing units before radiation levels rise further is becoming very important," said Japan Nuclear and Industrial Safety Agency senior official Hidehiko Nishiyama.
The 9.0 magnitude quake and giant waves on March 11 left more than 10,000 people dead and 17,000 missing.
Despite such a shocking toll, much attention since the disaster has been on the possibility of a catastrophic meltdown at Fukushima.
With elevated radiation levels around the plant triggering fears across the nation, storage of the contaminated water has to be handled carefully.
"We are working out ways of safely bailing out the water so that it does not get out into the environment, and we are making preparations," Nishiyama said.
He initially said the high radiation reading meant there could be damage to the reactor, but he later said it could be from venting operations to release pressure or water leakage from pipes or valves.
"There is no data suggesting a crack," he said.
Nuclear watchdog the International Atomic Energy Agency (IAEA) said on Friday there had not been much change in the crisis over the previous 24 hours.
"Some positive trends are continuing but there remain areas of uncertainty that are of serious concern," agency official Graham Andrew said in Vienna, adding the high radiation could be coming from steam.
On Friday, Nishiyama chided plant operator Tokyo Electric Power Co (TEPCO) for not following safety procedures inside the turbine building. Local media also criticized TEPCO, which has a poor safety record.
"The people on the spot have a strong sense of mission and may be trying to rush," the Nikkei business paper said. "But if the work is done hastily, it puts lives at risk and in the end, will delay the repairs. This kind of accident ought to have been avoidable by proceeding with the work cautiously."
More than 700 engineers have been working in shifts to stabilize the plant and work has been advancing to restart water pumps to cool their fuel rods.
Two of the plant's reactors are now seen as safe but the other four are volatile, occasionally emitting steam and smoke. However, the nuclear safety agency said on Saturday that temperature and pressure in all reactors had stabilized.
When TEPCO restored power to the plant late last week, some thought the crisis would soon be over. But two weeks after the earthquake, lingering high levels of radiation from the damaged reactors has kept hampering workers' progress.
At Three Mile Island, the worst nuclear power accident in the United States, workers took just four days to stabilize the reactor, which suffered a partial meltdown. No one was injured and there was no radiation release above the legal limit.
At Chernobyl in the Ukraine, the worst nuclear accident in the world, it took weeks to "stabilize" what remained of the plant and months to clean up radioactive materials and cover the site with a concrete and steel sarcophagus.
Japanese Prime Minister Naoto Kan said on Friday the situation at Fukushima was "nowhere near" being resolved.
"We are making efforts to prevent it from getting worse, but I feel we cannot become complacent," Kan told reporters. "We must continue to be on our guard."
RADIATION IN TOKYO WITHIN GLOBAL AVERAGE RANGE
In Tokyo, a metropolis of 13 million people, a Reuters reading on Saturday morning showed ambient radiation of 0.22 microsieverts per hour, about six times normal for the city.
However, this was well within the global average of naturally occurring background radiation of 0.17-0.39 microsieverts per hour, a range given by the World Nuclear Association.
Meanwhile, the Japanese government has prodded tens of thousands of people living in a 20 km-30 km (12-18 mile) zone beyond the stricken complex to leave, but insisted it was not widening a 20 km evacuation zone.
Opposition lawmakers and local officials were severely critical of the move, especially since it came after the government advised residents there to stay indoors.
"So far they have only given the irresponsible instruction to stay inside; the decision-making is slow," conservative Sankei newspaper quoted Toshikazu Ide, the mayor of a village inside the 20-30 km area, as saying.
Chief Cabinet Secretary Yukio Edano has said the residents should move because it was difficult to get supplies to the area, and not because of elevated radiation.
An official at the Science Ministry however confirmed that daily radiation levels in an area 30 km (18 miles) northwest of the plant had exceeded the annual limit.
Vegetable and milk shipments from near the stricken plant have been stopped, and Tokyo's residents were told this week not to give tap water to babies after contamination from rain put radiation at twice the safety level.
It dropped back to safe levels the next day, and the city governor cheerily drank tap water in front of cameras.
Experts say radiation from the plant is still generally below levels of exposure from flights or medical X-rays.
Nevertheless, South Korea, Taiwan, Singapore, Australia, the United States and Hong Kong are restricting food and milk imports from the zone. Other nations are screening Japanese food, and German shipping lines are simply avoiding the country.
In Japan's north, more than a quarter of a million people are in shelters. Exhausted rescuers are still sifting through the wreckage of towns and villages, retrieving bodies.
Amid the suffering, though, there was a sense the corner was being turned. Aid is flowing and phone, electricity, postal and bank services have resumed, though they can still be patchy.
(Additional reporting by Kazunori Takada, Kiyoshi Takenaka and Phil Smith in Tokyo, Jon Herskovitz in Kamaishi, and Michael Shields and Sylvia Westall in Vienna; Writing by Raju Gopalakrishnan; Editing by John Chalmers)