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Monday, March 21, 2011

Electricity restored at reactor No. 2


By MASAMI ITO and JUN HONGO
Staff writers

Tokyo Electric Power Co. restored electricity to the power center of the Fukushima No. 1 power plant's No. 2 reactor Sunday afternoon and will attempt to turn on its cooling system and other safety equipment to get the upper hand on the nuclear crisis.

News photo
Stricken: A satellite photo taken Friday shows damage to the buildings that house reactors No. 3 (right) and No. 4 at the Fukushima No. 1 nuclear plant. KYODO PHOTO/DIGITALGLOBE

Tepco is working round the clock to connect lengthy power cables to the crippled plant, where four of its six reactors have leaked or are continuing to leak radiation.

The March 11 quake and tsunami cut off all power to the reactors, killing critical safety features — most notably the systems that cool the fuel rods in the cores and the spent fuel rods stored in their containment pools — allowing them to get dangerously hot.

The No. 2 reactor is the first of the six to have power restored from outside the plant.

Tepco will first try to turn on the lights in the central control room before moving to power up instruments that measure pressure, temperature and radiation inside the reactor. If successful, the next step will be to turn on the cooling systems.

Also critical is determining whether any equipment was destroyed by the earthquake or seawater.

Strong radiation is making it difficult for workers to stay in the area long enough to connect power cables to reactors 3 and 4, Tepco said.

Meanwhile, reactors 5 and 6 were stable Sunday after cold shutdowns executed at the facilities succeeded after emergency power was restored by generators Saturday, authorities said.

Earlier in the day, firefighters and Self-Defense Forces personnel continued to direct streams of seawater at the buildings housing the No. 3 and 4 reactors, hoping to fill pools containing the overheating spent fuel rods.

In all since Thursday, 2,600 tons of seawater have been shot at the pool in the No. 3 reactor. It's unknown how much water actually entered the pool, which has a capacity of 1,400 tons.

At one point the same day, the pressure in the No. 3 reactor was rising, prompting Tepco to consider releasing more radioactive gas into the environment to avert serious damage to the containment vessel, the nuclear safety agency said Sunday afternoon.

But officials later backtracked and 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.

Tepco 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, which contains water. By going through the suppression pool, the reactor's steam would liquefy before being released to lower the pressure inside the containment vessel.

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, they may have to 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 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," he said.

Meanwhile, efforts continued on all fronts at the 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.

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 revealed Sunday that one of its workers has been exposed to more than 100 millisieverts while on-site.

Information from Kyodo added.


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