Home > SOCIETY > Japan:TEPCO – Reactor may have gone critical + Related Articles

Japan:TEPCO – Reactor may have gone critical + Related Articles

Wednesday, November 2, 2011

Laaska News  Nov. 2 ,2011

The operator of the crippled Fukushima Daiichi nuclear power plant says it found in the facility’s No.2 reactor radioactive substances that could have resulted from continuous nuclear fission.

The Tokyo Electric Power Company, or TEPCO, said on Wednesday that it detected xenon-133 and xenon-135 in gas taken from the reactor’s containment vessel on the previous day. The substances were reportedly in concentrations of 6 to more than 10 parts per million becquerels per cubic centimeter.

Xenon-135 was also detected in gas samples collected on Wednesday.

Radioactive xenon is produced during nuclear fission.
The half-life of xenon-133 is 5 days, and that of xenon-135 is 9 hours.

TEPCO says the findings suggest that nuclear fission may have occurred recently, not just after the March 11th accident, and that a state of criticality could have occurred temporarily in some areas.

TEPCO workers poured a boric acid solution into the reactor on Wednesday to suppress nuclear fission.

The utility says it has not found any significant change in temperature and pressure of the reactor, and that large-scale criticality did not occur.

TEPCO says the reactor’s cooling process is continuing and that the firm expects to achieve cold shutdown at the plant this year as planned. But the utility also says it wants to take a close look at the situation of the plant’s No.1 and 3 reactors.

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Genkai reactor resumes power generation


A reactor at the Genkai nuclear plant in Saga Prefecture, southwestern Japan, has resumed power generation after a nearly monthlong stoppage.

The resumption at the plant’s No. 4 reactor took place on Wednesday afternoon. The reactor had stopped generating power automatically on October 4th due to a procedural error.

The plant’s operator, Kyushu Electric Power Company, restarted the reactor on Tuesday after getting the go-ahead from the Nuclear and Industrial Safety Agency.

Kyushu Electric plans to gradually increase the amount of power generated and return to normal operation by Friday.

The plant is the first in Japan to resume operation after the March accident at Fukushima Daiichi nuclear plant.

The reactor is scheduled to be stopped for a regular inspection next month.
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Nuke watchdog says fresh meltdown unlikely


Japan’s nuclear watchdog says it believes another meltdown at the Fukushima Daiichi nuclear power plant is unlikely, but will continue to monitor the situation closely.

The Nuclear and Industrial Safety Agency held a news conference on Wednesday, after radioactive xenon was detected in the containment vessel of the No.2 reactor. The presence of the substance indicates that nuclear fission may have briefly resumed.

The safety agency says it is unlikely that nuclear fuel has begun melting again, as the density of xenon is low and there has been no change in the reactor’s temperatures.

The agency also says it will closely monitor if xenon continues to be detected after Tokyo Electric Power Company poured boric acid solution into the reactor to suppress nuclear fission.

It added that it cannot yet say how the latest development will affect the government’s plan to achieve a cold shutdown of the disabled reactors by the end of the year.

Senior official Yoshinori Moriyama said it is difficult to determine the amount of nuclear fuel remaining in the containment vessel of the No.2 reactor. He said his agency will assess the situation and judge if it is still possible to stably lower temperatures in the reactor and containment vessel.

 

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TEPCO: New criticality seen at No.2 reactor

 

The operator of the Fukushima Daiichi power plant says the No.2 reactor may have recently gone critical.

Tokyo Electric Power Company said on Wednesday its latest findings suggest that the state of criticality may have continued temporarily.

TEPCO detected radioactive substances, xenon-133 and xenon-135, in gas taken from the reactor’s containment vessel on Tuesday. Both materials are produced during nuclear fission and have a short half-life of 5 days and 9 hours respectively.

The xenon-133 registered 14 parts per million becquerels per cubic centimeter, and the xenon-135 12 parts per million.

After detecting the xenon, TEPCO poured a boric acid solution into the No.2 reactor to suppress nuclear fission. It said temperature and pressure in the reactor are basically unchanged.

The operator says the reactor continues to cool, and that it expects to achieve cold shutdown by the end of the year as planned.

It says it will continue to monitor xenon levels in the No.2 reactor and also check conditions in the No.1 and No.3 reactors.

TEPCO adds it will discuss the matter with the government’s Nuclear and Industrial Safety Agency.
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Temperature, pressure unchanged in No.2 reactor

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TEPCO says temperature and pressure in the No.2 reactor at the Fukushima Daiichi nuclear power plant is basically unchanged in a 24-hour period between Tuesday and Wednesday.

The company says the temperature at the bottom of the reactor was 76 degrees Celsius as of 5 AM on Wednesday. That was down 1.4 degrees from 24 hours earlier.

The reactor’s pressure gauge registered 0.007 megapascals at 5 AM on Wednesday, down one part per thousand from the same time on Tuesday .
NHK.

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