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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: Yay!!
By Ushio01 on 5/13/2011 7:41:53 PM , Rating: 1
Or maybe we can start in 150 years when the Cs-137 decays to acceptable levels?

You mean 70 days.

RE: Yay!!
By PaterPelligrino on 5/13/2011 8:21:07 PM , Rating: 2
The phrase "decays to acceptable levels" is vague enough to offer a lot of wriggle room, and I'm not sure what the answer to that is; however, the half-life of Cesium-137 is 30 years.

It is the biological half-life of Cesium-137 that is 70 days, meaning that 70 days after ingestion , it loses half of it's radioactive toxicity through elimination, etc.

The Cesium-137 released by the Chernobyl meltdown 20 years ago is still a threat to human health.

RE: Yay!!
By randomly on 5/13/2011 8:30:50 PM , Rating: 3
Cs-137 has a 30 year half life. In 150 years 97% will have decayed away.

Almost none of it will have decayed in 70 days.

You may be thinking of the iodine-131 which has an 8 day half life. Only 1 part in a thousand will be left after 80 days, in 160 days only 1 millionth of the I-131 will be left, including whatever was in the seaweed.

Although the CS-137 lasts much longer, the iodine is more of a concern because of how strongly the body absorbs and concentrates it in the thyroid. CS-137 is thousands of times less hazardous because it's not readily absorbed or concentrated in tissues to the degree that iodine is.

Fortunately there will be almost no radioactive iodine left in a few months. Only about 1/200th of the original I-131 is left currently.

on the other hand your comment about 70 days is also partly valid since radiation levels for almost all areas except the plant itself are already fairly low.

RE: Yay!!
By drewsup on 5/15/11, Rating: 0
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