Pressure within the No. 3 reactor at the Fukushima No. 1 nuclear plant was rising at one point and Tepco considered releasing more radioactive gas into the environment to avert serious damage to the containment vessel, the nuclear safety agency said Sunday afternoon.
Kyodo News
In this Sept. 2010 photo, an operator works at Unit 3 reactor of the Fukushima Daiichi Nuclear Power Plant in Okumamachi, Fukushima Prefecture in Japan.
However, officials later said the pressure in the vessel, which houses lethal radioactive materials, had stabilized. They said they would observe the situation carefully and "not immediately" take the risky measure.
Tokyo Electric Power Co. had considered releasing the contaminated steam directly into the environment, not through a "suppression pool" as it did earlier in the crisis.
Even so, the government said it wasn't necessary to expand the evacuation area beyond the current 20-km radius from the plant.
The pressure needs to be lowered to protect the structural integrity of the reactor, and the first step is to open the valve on a pipe connected to the suppression pool. By going through the suppression pool, the reactor's gas would liquefy and thus lower the pressure.
But if the pool is already filled with water, a valve on the reactor itself would need to be opened and the radiation level of the released gas would be higher than with the first method, explained Hidehiko Nishiyama of the Nuclear and Industrial Safety Agency.
"Without water, there would be more radioactive substances in the gas released into the environment," Nishiyama said.
Nishiyama added that if the trickier option is used, it may be necessary to temporarily evacuate Tepco staff from the plant.
The government has evacuated people within 20 km of the plant, and those between 20 to 30 km are being told to stay inside.
Amid concern that rain might soon fall in the area, Nishiyama stressed that the radiation level was not high enough to affect people's health but urged people to avoid getting wet.
"The level (of radiation) has no impact on the human body. But it's better that people should try not to get hit by the rain as much as possible," Nishiyama said.
Meanwhile, efforts continued on all fronts at the crippled plant, as work on restoring electricity and spraying seawater on the overheated nuclear reactors continued around the clock.
Tepco said it was making progress on rebuilding the electrical grid that was knocked out by the March 11 earthquake and tsunami.
In addition to rebooting the cooling system, Tepco hopes it can get a detailed picture of the damage once electricity in the power plant's central control room is restored.
Tepco said it succeeded in bringing power cables to reactors 1 and 2 but hadn't completed the necessary checks to restart equipment.
The operator can't restart the cooling systems for the reactors until it confirms the damage to the transformers, motors, pumps and other gear, a Tepco official said, adding that it was unlikely the procedures would be finished by the end of Sunday.
Tepco also said power cables will hopefully reach reactors 3 and 4 by Monday, and electricity could be provided Tuesday, although that process has been delayed by the need to do some rerouting.
The spent fuel rod pool at reactor 4, which reached 84 degrees last week, was doused by Self-Defense Forces fire engines with seawater Sunday morning.
Reactors 5 and 6, which were not operating when the earthquake hit but whose spent fuel rod pools saw a rise in temperature, appeared to be the most stable Sunday afternoon.
Tepco also revealed Sunday that one of its workers has been exposed to more than 100 milllisieverts while on-site.
©japantimes.co.jp
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