Japan: Nuke Radiation Fatally High

Wednesday, March 28, 2012 @ 02:03 PM gHale

One of Japan’s crippled nuclear reactors still has fatally high radiation levels and much less water to cool it than officials had thought.

A tool equipped with a tiny video camera, a thermometer, a dosimeter and a water gauge was able to assess damage inside the No. 2 reactor’s containment chamber for the second time since an earthquake and tsunami struck the Fukushima Dai-ichi plant a year ago.

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The No. 2 reactor is the only one officials have been able to closely examine so far. What that says about the other two reactors remains up in the air.

The data collected showed the damage from the disaster is so severe, the plant operator will have to develop special equipment and technology to tolerate the harsh environment and decommission the plant, a process expected to last decades.

The examination with an industrial endoscope detected radiation levels up to 10 times the fatal dose inside the chamber. Plant officials previously said more than half of the melted fuel has breached the core and dropped to the floor of the primary containment vessel, some of it splashing against the wall or the floor.

Particles from melted fuel have sent radiation levels up to a dangerously high 70 sieverts per hour inside the container, said Junichi Matsumoto, spokesman for Tokyo Electric Power Co. The figure far exceeds the highest level previously detected, 10 sieverts per hour, detected around an exhaust duct shared by No. 1 and 2 units last year.

The probe also found the containment vessel — a beaker-shaped container enclosing the core — had cooling water up to only 60 centimeters (two feet) from the bottom, far below the ten meters (11 yards) estimated when the government declared the plant stable in December. The plant is continuing to pump water into the reactor.

Video footage taken by the probe showed the water inside was clear but contained dark yellow sediments, believed to be fragments of rust, paint that had peeled off or dust.

A probe in January failed to find the water surface and provided only images showing steam, unidentified parts and rusty metal surfaces scarred by exposure to radiation, heat and humidity. Finding the water level was important to help locate damaged areas where radioactive water is escaping.

Matsumoto said the water level inside the chamber was way off the estimate, which had used data that turned out to be unreliable. But the results do not affect the plant’s ‘cold shutdown status’ because the water temperature was about 50C (122F), indicating the melted fuel is cooled.

Three Dai-ichi reactors had meltdowns, but the No. 2 reactor is the only one examined because radiation levels inside the reactor building are relatively low and its container has a convenient slot to send in the endoscope.

The exact condition of the other two reactors, where hydrogen explosions damaged their buildings, is still unknown. Simulations indicated more fuel inside No. 1 breached the core than the other two, but radiation at No. 3 remains the highest.

The high radiation levels inside the No. 2 reactor’s chamber mean it is inaccessible to workers, but parts of the building are accessible for a few minutes at a time.

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