Sunday, May 15, 2011

Fukushima Disaster Continues

Accurate data destroys optimistic TEPCO assessment, hampers cooling plan (Asahi.com)

Accurate data shattered the overly optimistic assessment of Tokyo Electric Power Co. concerning the crippled Fukushima No. 1 nuclear power plant and raised doubts about the company's game plan for ending the crisis.

Measurements from a recently installed water gauge provided conclusive evidence that the condition of the No. 1 reactor at the plant was much more serious than TEPCO officials have acknowledged until now.

TEPCO officials admitted on May 12 that a "meltdown" had occurred in the No. 1 reactor. Fuel rods had melted, and the molten fuel accumulated and caused small cracks at the bottom of the reactor pressure container, they said.

Until now, TEPCO officials only said that fuel rods were partially damaged and compiled a work schedule in April for restoring a stable cooling system based on that assumption.

Despite being unable to obtain accurate measurements from gauges in the reactors damaged in the March 11 Great East Japan Earthquake, TEPCO officials still made those optimistic assumptions.

From immediately after the quake, the measurements from the water gauge at the No. 1 reactor showed very little change, casting doubt on the reliability of the instruments.

After workers entered the No. 1 reactor building and adjusted the water gauge, the data obtained showed water levels so low that the gauge was unable to measure it.

TEPCO officials concluded that water had accumulated in only about 20 percent of the volume of the No. 1 reactor's pressure container.

Other specialists had long warned that the situation at the No. 1 reactor was much more serious than the scenario that TEPCO officials were presenting.

At a news conference April 1, Shunichi Tanaka, a former vice chairman of the Japan Atomic Energy Commission, said all the fuel rods in the No. 1 reactor had melted, raising the possibility of damage to the pressure container.

TEPCO's latest measurements found the temperature of the pressure container was about 100 degrees. If the fuel rods had been exposed because of the low water level, the temperature should have been much higher. The only explanation is that the fuel rods melted, accumulated at the bottom of the pressure container and the melted fuel was cooled by the small volume of water at the bottom.

The No. 1 reactor is not the only one with problems. Small cracks have probably also developed at the bottom of the pressure containers of the No. 2 and No. 3 reactors.

Evidence of that possibility is the highly contaminated water found in the basements of the turbine buildings of the three reactors as well as underground trenches.

The contamination was likely caused by water leaking from the bottoms of the pressure containers of the three reactors.

TEPCO officials now admit that the measurements from the water gauges at the pressure containers in the No. 2 and No. 3 reactors are also unreliable.

While those water gauges will have to be repaired as soon as possible, TEPCO will also have to review its work schedule for cooling the reactors.

That will likely mean rethinking the plan to submerge the containment vessel of the No. 1 reactor in water to cool the pressure container within.

About 10,000 tons of water have already been pumped into the No. 1 reactor's pressure container, but about 3,000 tons of that water are unaccounted for. That likely means the water has leaked out of the containment vessel.

Moreover, if TEPCO continues to pump in water to the reactors to cool them, water contaminated with radiation will continue to leak out from the cracks at the bottoms of the pressure containers.

TEPCO officials have also not denied the possibility that melted fuel has leaked out of the pressure container. That would mean the volume of contaminated water will likely increase, making work in the reactor buildings much more difficult.


Setbacks at Japan nuclear plant(BBC)

A reactor at Japan's crippled nuclear plant has been more badly damaged than originally thought, operator Tepco has said.

Water is leaking from the pressure vessel surrounding reactor 1 - probably because of damage caused by exposed fuel rods melting, a spokesman said.

Contaminated water had also entered the sea from a pit near reactor 3 but this had now been stopped, he said...

He said there was likely to be a large leak in the pressure vessel, possibly caused by the fallen fuel.

"As for a meltdown, it is certain that it has crumbled and the fuel is located at the bottom (of the vessel)," he added.

The water is said to be leaking into the containment vessel and from there into the reactor building.

Experts said the announcement from Tepco did not mean that the situation at the plant had worsened because it was likely that the fuel had dropped to the bottom of the core soon after the 11 March earthquake.

Japan nuclear: Tepco halts Fukushima cooling plan(BBC)

Japanese engineers have abandoned their latest attempt to stabilise a stricken reactor at the Fukushima nuclear plant.

The plant's operator, Tepco, had intended to cool reactor 1 by filling the containment chamber with water.

But Tepco said melting fuel rods had created a hole in the chamber, allowing 3,000 tonnes of contaminated water to leak into the basement of the reactor building.

The power plant was badly damaged by the earthquake and tsunami on 11 March.

Cooling systems to the reactors were knocked out, fuel rods overheated, and attempts to release pressure in the chambers led to explosions in the buildings housing the reactors.

The government and Tepco (Tokyo Electric Power Company) said it would take until next January to achieve a cold shut-down at the plant.

Government spokesman Goshi Hosono said the latest setback would not affect the deadline...

Last week the government agreed a huge compensation package for those affected by the disaster.

Analysts say the final bill for compensation could top $100bn (£61bn).
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More info can be found @ Radiation Safety Philippines

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