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Danger level radiation after 3rd blast at Japan nuclear plant

Wed 2011-Mar-16 @ +08 02:15:31 am

Experts say minimal health risks beyond 12-mile (20km) radius

The Guardian
Engineers were struggling to regain control of the Fukushima plant following another explosion early on Tuesday and a fire that caused a spike in radiation to harmful levels. Seventy technicians are still battling to cool reactors at the Fukushima Daiichi facility but non-essential personnel have been ordered to leave. Kyodo news agency said radiation levels have become too high for staff to remain in control rooms.

The power plant was rocked by an explosion at the No 2 reactor, the third blast at the site in four days. That was followed by a fire that broke out at the No 4 reactor unit, which appeared to be the cause of Tuesday’s radiation leaks. That reactor was shut down for maintenance before the earthquake, but its spent fuel rods are stored in a pool at the site. The fire was later extinguished but Kyodo reported that the pool was subsequently boiling, with the water level falling. If the water boils off there is a risk that the fuel could catch fire, sending a plume of radiation directly into the atmosphere.

Radiation levels at one location on the site reached 400 millisieverts (mSv) an hour after the fire – four times the level that can lead to cancer – the chief cabinet secretary, Yukio Edano, said. But levels had lowered dramatically by the end of the day, according to the International Atomic Energy Authority.

The government ordered any inhabitants remaining within the 12-mile (20km) radius exclusion zone to leave immediately, told those between 12 miles and 19 miles away to stay indoors and imposed a 19-mile no-fly zone. Experts backed their assessment that health risks beyond that area were minimal at present.
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Helicopter water-bombs to cool boiling fuel rod pond

New York Times
A small crew of technicians braved radiation and fire through Tuesday as they fought to prevent three nuclear reactors in northeastern Japan from melting down and stop storage ponds loaded with spent uranium fuel pods from bursting into flames.

Taking shelter when possible in the reactor’s control room, which is heavily shielded from radiation, they struggled through the morning and afternoon to keep hundreds of gallons of seawater a minute flowing through temporary fire pumps into the three stricken reactors, where overheated fuel rods continued to boil away the water at a brisk pace.

Power company officials said that they would consider using helicopters in an attempt to douse with cold water a boiling rooftop storage pond for spent uranium fuel rods. The rods are still radioactive and potentially as hot and dangerous as the fuel rods inside the reactors if not kept submerged in water.

“The only ideas we have right now are using a helicopter to spray water from above, or inject water from below,” an official. “We believe action must be taken by [Wednesday or Thursday].”

Hydrogen gas bubbling up from chemical reactions set off by the hot fuel rods produced a powerful explosion on Tuesday morning that blew a 26-foot-wide hole in the side of reactor No. 4 at the Fukushima Daiichi nuclear power plant. A fire there may have been caused by machine oil in a nearby facility according to an American official.
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