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RE: Fukushima No.1 nuclear plant
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Japan's nuclear safety agency said 70 per cent of the nuclear fuel rods may have been damaged at Fukushima Reactor No. 1, which suffered an explosion Saturday, triggering the crisis. The Kyodo news agency said 33 per cent of the fuel rods at Reactor No. 2, which was hit by an explosion on Tuesday, have also been damaged. The reactors' cores are believed to have partly melted after the cooling mechanisms shut down.
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Spent rods submerged in the pool next to the Unit 4 reactor

Spent fuel at the complex is an increasing focus of concern. Tepco had moved all of the rods from the Unit 4 reactor to the spent-fuel pool sometime after Dec. 1 as part of routine maintenance, meaning the pool contained not only all of the rods accumulated from many years of service but also all of those currently in use.
In 2006, the National Academy of Sciences issued a report warning that a loss of cooling water or circulation could trigger a catastrophic fire in a spent-fuel pool that would result in large releases of radioactive material. If the rods become exposed to the air, their zirconium tubes begin to react with oxygen and heat up even more, a type of oxidation fire. At some point, the material inside the tubes melts and can release highly radioactive isotopes such as cesium-137 and iodine-131.

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Unit 2 Explosion and Unit 4 Spent Fuel Pool Fire

It was reported earlier today that the explosion at Unit 2 of the Fukushima Daiichi plant damaged the suppression chamber.
Hydrogen gas from the cladding oxidation with steam collected in the suppression pool and ignited.  This scenario differs from those of units 1 and 3 where the explosion occurred outside the primary containment in the upper part of the reactor building. 
This breach of primary containment is certainly more serious than the situation in units 1 and 3.  Seawater is still being pumped in the containment and the reactor vessel.  At this time radioactive releases from unit 2 have been similar to the ones seen from units 1 and 3.

Source

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New fire hits Japan nuclear plant

There has been a fresh fire at the quake-stricken Fukushima Daiichi nuclear plant in northern Japan.
The new blaze began at reactor four. The plant has already been hit by four explosions, triggering radiation leaks and sparking health concerns.

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Concerns shift to reactors 2 and 4

The Fukushima crisis has followed an unpredictable path from the beginning.
When the earthquake hit on Friday and three operating reactors shut down as planned, no one expected all the back-up cooling equipment to be knocked out by the tsunami. No one foresaw the spectacular explosions that destroyed outer buildings at the reactors. And, with everyone focusing on the reactors, Tuesday's shift of attention to a cooling pond for spent nuclear fuel came as a complete surprise.

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Professor Paddy Regan, a nuclear physicist, says the Japanese authorities are doing a good job over the Fukushima radiation leaks.

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The Japanese authorities have informed the IAEA that the following radiation dose rates have been observed on site at the main gate of the Fukushima Daiichi Nuclear Power Plant.
At 00:00 UTC on 15 March a dose rate of 11.9 millisieverts (mSv) per hour was observed. Six hours later, at 06:00 UTC on 15 March a dose rate of 0.6 millisieverts (mSv) per hour was observed.
These observations indicate that the level of radioactivity has been decreasing at the site.
As reported earlier, a 400 millisieverts (mSv) per hour radiation dose observed at Fukushima Daiichi occurred between units 3 and 4. This is a high dose-level value, but it is a local value at a single location and at a certain point in time. The IAEA continues to confirm the evolution and value of this dose rate. It should be noted that because of this detected value, non-indispensible staff was evacuated from the plant, in line with the Emergency Response Plan, and that the population around the plant is already evacuated.
About 150 persons from populations around the Daiichi site have received monitoring for radiation levels. The results of measurements on some of these people have been reported and measures to decontaminate 23 of them have been taken. The IAEA will continue to monitor these developments.
Evacuation of the population from the 20 kilometre zone is continuing. The Japanese have asked that residents out to a 30 km radius to take shelter indoors. Japanese authorities have distributed iodine tablets to the evacuation centres but no decision has yet been taken on their administration.

Source International Atomic Energy Agency (IAEA)

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Low-levels of  radiation have been detected south of Tokyo.  However, the Fukushima nuclear plant now seems to be under control.

The Navy said very low levels of airborne radiation were detected Tuesday morning at greater Tokyo-area bases in Yokosuka and Atsugi, prompting commanders to direct base residents to remain indoors as a precaution.
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It appears that for the first time, the containment system around one of the Fukushima Daiichi reactors has been breached.
Officials have referred to a possible crack in the suppression chamber of reactor 2 - a large doughnut-shaped structure, also known as the torus, below the reactor housing.
That would allow steam, containing radioactive substances, to escape continuously.
This is the most likely source of the high radioactivity readings seen near the site.
However, an alternative possible source is the fire in reactor 4 building - believed to have started when a pool storing old fuel rods dried up.
When fuel rods reach the end of their useful life and are taken from the reactor, they still contain a lot of radioactive nuclei, which means they get hot.
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Spent fuel rods containing radioactive material may have burned in Tuesday's fire at the Fukushima Daiichi nuclear plant -- causing a spike in radiation levels, the plant's owner said.
The blaze started Tuesday morning but was later extinguished, Tokyo Electric Power Company said. It was unclear how much radioactive material may have been emitted, or what kind of health threat that could pose.

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Ed ~ The fire at the Fukushima Daiichi nuclear power plant was extinguished on March 15 at 0200 UTC

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Japan earthquake: New blast at Fukushima nuclear plant

A fresh explosion has been heard at a quake-hit nuclear plant in northern Japan, local media say.
Technicians have been battling to stabilise reactor 2 at the Fukushima Daiichi plant, after two other reactors exploded in three days.
International nuclear watchdogs said there was no sign of a meltdown but one minister said it was "highly likely" that the rods might melt.

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