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Tepco engineers use concrete to seal leaks  (Source: TEPCO)
The top five feet of the core's 13 ft-long fuel rods had melted down after being exposed to the air

The Tokyo Electric Power Company (Tepco) has announced that the No. 1 reactor at the Fukushima Daiichi nuclear power plant has suffered a nuclear meltdown.

The Fukushima Daiichi nuclear power plant was first commissioned in 1971 and is located in the Futaba District of Fukushima Prefecture, Japan. On March 11, 2011, a 9.0-magnitude earthquake struck Japan, resulting in the disabling of reactor cooling systems, radiation leaks and an evacuation zone. 

Engineers from Tepco entered the No. 1 reactor for the first time at the end of last week and found that the top five feet of the core's 13 ft-long fuel rods had melted down after being exposed to the air. 

Engineers originally thought only 55 percent of the core was damaged since it was submerged in enough water to keep cool and stable, but after discovering a pool of molten fuel at the bottom of the containment vessel, they now worry that this molten fuel burned a hole at the bottom of the vessel prompting water to leak. 

Tepco recently sealed a leak at the No. 3 reactor after radioactive water had seeped into the ocean. Also, the No. 2 reactor had radioactive water flowing into the ocean in April. According to Greenpeace, "significant amounts" of radioactive material had slipped into the sea. In fact, illegal amounts of iodine and caesium were found in seaweed as far as 40 miles from the Fukushima Daiichi plant. 

In 22 samples of seaweed, ten contained five times the legal limit of iodine 131 and 20 times of caesium 137. This is an issue for several reasons, including the fact that the Japanese household consumes almost 7 lbs of seaweed annually, and fisherman are preparing to harvest this seaweed on May 20. 

Engineers have decided to quit flooding the entire reactor core with water because it might make the leak worse. Currently, there is plenty of water at the bottom of the containment vessel to keep the remaining fuel rods and the melted fuel cool. 

"We will have to revise our plans," said Junichi Matsumoto, Tepco spokesman. "We cannot deny the possibility that a hole in the pressure vessel caused water to leak."


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RE: *Partial* meltdown
By Hoser McMoose on 5/15/2011 9:38:11 PM , Rating: 1
"Partial meltdown", "full meltdown", or whatever other type of "meltdown" you wish to describe, doesn't have any proper meaning. That is why the term is never used in any technical description, it just doesn't accurately describe anything.

It's used in movies and by the media to generically describe any sort of problem with any sort of nuclear equipment that has had any sort of "melting" (for a variety of definitions of "melting").

So really calling it a "partial meltdown" or a "full meltdown" is equally accurate and also equally useless for describing what is actually happening.


RE: *Partial* meltdown
By SPOOFE on 5/16/2011 12:01:15 AM , Rating: 4
That's like saying the term "car crash" is useless, because it can mean anything from a fender-bender all the way up to an 80-car pile-on.

Nope; the melting of nuclear fuel is about the worst thing that can happen in a nuclear reactor. As such, the term "meltdown" has a hell of a useful meaning. It's just not very pleasant.


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