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Japan:Panel studies aging effect on Fukushima accident

Tuesday, November 29, 2011

Laaska news  Nov. 29,2011
Expert urges probe of No.2 reactor leak

TEPCO says no explosion occurred at No.2 reactor

Panel studies aging effect on Fukushima accident

Japanese nuclear experts are investigating how the aging of facilities factored into the accident that struck the Fukushima Daiichi nuclear power plant in March.

The Nuclear and Industrial Safety Agency, together with a panel of experts, has begun studying regulations on aging nuclear plants. Nineteen — or more than one-third of all reactors in Japan, including those in Fukushima — began their operations more than 30 years ago.

In their first meeting on Tuesday, the panel’s secretariat reported that the Fukushima Daiichi plant shut down automatically after the March 11th quake, and emergency power generators were working until the tsunami struck.

The staff said that facility aging did not appear to have been an issue in the accident.

The Fukushima plant lost all electricity sources on the day of the disaster, which caused meltdowns at 3 of the reactors.

But some experts said it is too early to determine causal relations of the accident at this point.

The government panel decided to study whether the age of facilities played a role in the accident before making revisions to its safety regulations for aging reactors.

In the meeting, the experts also reported that steel used for a 36-year-old reactor at the Genkai nuclear plant in southwestern Japan has become weaker than estimated.

Some members said that to win local approval to continue operating the reactor, the reason why this happened must be determined as soon as possible.
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TEPCO says no explosion occurred at No.2 reactor

The operator of the damaged Fukushima Daiichi nuclear power plant says there was no explosion at the No. 2 reactor, denying an earlier report that there was. But the company says it is still unable to determine how and why radioactive substances were released from the reactor.

NHK has obtained Tokyo Electric Power Company’s interim report on the nuclear accident that was triggered by the earthquake and tsunami on March 11th.

The report includes findings from a study that the utility launched in June to analyze how the accident occurred and how workers responded to it.

The report says that almost all electricity sources for the reactors were lost at once following the tsunami.

As a result, multiple safety functions were also lost, causing meltdowns from the No. 1 to the No. 3 reactors.

TEPCO analyzed seismographic data recorded within the plant in the early morning of March 15th, 4 days after the disaster, when a large blast was reportedly heard near the containment vessel of the No. 2 reactor.

The company concluded in the report that there was no explosion at the No. 2 reactor, and that a blast at the No. 4 reactor was mistakenly believed to have occurred at the No. 2.

Later that day, pressure inside the No. 2 reactor vessel dropped sharply, and radiation levels near the plant’s main gate rose above 10 millisieverts per hour, then the highest level so far.
The interim report fails to specify how the leakage occurred at the containment vessel, just saying that gas in the vessel was somehow released into the air.

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Expert urges probe of No.2 reactor leak

The spike in radiation levels following unspecified trouble at the No.2 reactor on March 15th was much more prominent than on March 12th or 14th, when explosions hit the No.1 and No.3 reactors.

Shinichiro Kado, an associate professor at the University of Tokyo, calls the reactor containment vessel “a final fortress” for keeping radioactive substances trapped, and a “cornerstone” for the integrity of a nuclear plant.

Kado says a breach of the vessel is extremely grave.

He says TEPCO needs to clarify how radioactive substances were released, by cross-referencing data on reactor conditions and patterns of radioactive dispersion in the atmosphere.
NHK.
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Laaska News.
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