Japan's nuclear safety officials reprimanded the operator of Japan's tsunami-damaged power plant Friday and demanded an investigation of how two workers were exposed to radiation more than twice a government-set limit.
The government also ordered the utility to reduce workers' risks of heat-related illnesses as concerns grow about the health risks faced by the people toiling to get the Fukushima Dai-ichi plant under control.
The two men with high radiation exposures worked at a central control room for two reactors when the tsunami struck March 11 and the days that followed. They are not showing immediate health problems but will need long-term monitoring for an increased risk of cancer, said the National Institute of Radiological Sciences, which examined the men.
Soon after the tsunami knocked out the plant's power and cooling systems, the government raised the radiation limit for men to 250 millisieverts from the standard 100 millisieverts so workers could tackle the emergency.
The two men, one in his 30s and the other in his 40s, were confirmed last week as having exceeding that higher limit and were removed from working at the plant. A third man _ a senior control room operator in his 50s _ is being tested further after early findings showed high radiation exposure as well, Tokyo Electric Power Co. spokesman Junichi Matsumoto said.
The Nuclear and Industrial Safety Agency reprimanded TEPCO for violating the limit and ordered the company to submit the cause and prevention measures in a report within a week.
The younger man was exposed to 678 millisieverts and the other man 643 millisieverts _ about 100 CT scans _ mostly by inhaling radioactive particles, NISA spokesman Hidehiko Nishiyama said.
TEPCO already has admitted that workers in the earliest, most chaotic, and most dangerous moments of the crisis did not wear masks, possibly other protective gear as well, and lacked dosimeters to monitor their radiation exposures in real time. TEPCO was previously warned for failing to provide a dosimeter for each worker entering controlled areas of the plant.
"The two men worked under an extremely harsh environment. It is truly regrettable that TEPCO put them to work under such conditions," Nishiyama said. He said NISA may consider a penalty on the operator, but did not elaborate.
A massive single whole-body exposure of 500 millisieverts could decrease lymphocyte cells in some people, which would compromise their immune systems. Radiation sickness, which has the signature symptoms of nausea and hair loss, can occur from an acute dose of 1,000 millisieverts.
The health and labor ministry has ordered TEPCO to check internal exposures of people who worked closely with the two men and to remove them from plant duties. About 150 were control room operators, likely to have been working nearby when the two men were exposed.
Nearly 4,000 people worked at the plant during March, when radiation leaks from the reactors were believed to be the highest. With two measuring machines available, about half of that group has been checked so far for their internal radiation levels, which involve exposure from breathing or ingesting radioactive particles. Further examination is pending.
Also Friday, the health ministry instructed TEPCO to take steps to reduce workers' risk of heat exhaustion and heat stroke. Workers have said full-face masks and protective coveralls in high temperatures make their work extremely strenuous.
At least a dozen workers have suffered heat illnesses at the plant, according to NISA and the health ministry, which did not give more details.
The ministry also ordered TEPCO to not put the workers on duty between 2 p.m. and 5 p.m. in July in August, when temperatures could exceed 30 Celsius (86F), and to tell workers to take water and salt and use caution. TEPCO is setting up dozens of rest areas across the plant so workers can take a break.
Last year, a total of 171 people died of heat strokes in Japan, including 47 at work.
Health concerns are also spreading outside the plant. The government says several areas outside the current evacuation zone are showing higher-than-expected cumulative radiation levels. Recent monitoring also detected strontium, an isotope that accumulate in bones and could increase cancer risks. The government is still considering whether to evacuate residents of tiny "hot spots" outside the 12-mile (20 kilometer) no-go zone.
More than 80,000 people have been forced to leave homes in that area.