By Kevin Krolicki
TOKYO (Reuters) - At least eight workers trying to bring Japan's crippled nuclear power plant under control have been exposed to more radiation than allowed under new safety standards, government officials said on Monday.
Three of six reactors at northeastern Fukushima melted down after the March 11 quake and tsunami knocked out power to the plant. Tens of thousands of people have been evacuated from the area around the plant.
The operator of the Fukushima Daiichi plant, Tokyo Electric Power, also known as Tepco, had previously said two workers had been exposed to more radiation than allowed.
The exposure of the additional six workers was discovered after almost 2,400 workers underwent testing, officials said.
Workers have been battling to bring the leaking reactors to a stable shutdown after the giant March 11 quake and tsunami that triggered the world's worst nuclear accident since Chernobyl in 1986.
Concerns about worker safety have been growing as the struggle to contain the crisis drags on and even Tepco acknowledges that it will be tough to hit a target of stabilizing the reactors by January.
Many experts on radiation believe that the risk of cancer and other disease rises with the amount of exposure.
"The development is extremely regrettable," said Hide Nishiyama, a spokesman for Japan's nuclear regulatory agency.
Nishiyama said the Nuclear and Industrial Safety Agency had told Tepco to investigate the cause of the exposure and to take steps to make sure that it was not repeated.
Japanese officials from embattled Prime Minister Naoto Kan on down have been widely criticized for their handling of the nuclear disaster, which has prompted a complete rethink on the future of nuclear energy in the quake-prone country.
The tsunami that crashed into the plant after the 9.0-magnitude earthquake has been estimated at around 14 meters (46 ft), nearly two-and-a-half times the height of the protective wall at Fukushima.
The quake and tsunami alone killed about 24,000 people.
(Reporting by Kevin Krolicki; Editing by Linda Sieg and Nick Macfie)