JAPAN | More high radiation spots found / Levels of 5 and 10 sieverts detected near pipe at No. 1 nuclear reactor

Posted on August 4, 2011

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JAPAN | YOMIURI SHIMBUN | 4 August 2011

Extremely high levels of radiation have been detected at two more locations near a pipe at the Fukushima No. 1 nuclear power plant, Tokyo Electric Power Co said.

The revelation was made Tuesday, a day after 10 sieverts (10,000 millisieverts) per hour was detected on the pipe, the highest radiation level recorded at the plant.

Full-body exposure to 10 sieverts of radiation is almost certainly lethal to humans.

According to Tuesday’s announcement, radiation levels in excess of 10 sieverts and 5 sieverts per hour were detected near the pipe connected to the containment vessel of the No. 1 reactor.

Radioactive materials are believed to have accumulated on the pipe after being released when the No. 1 reactor’s vents were opened in the wake of a meltdown at the facility in March. The vents are still releasing radiation, TEPCO believes.

About 2 grams of radioactive cesium releases radiation of 10 sieverts per hour.

The second location, from which radiation at 10 sieverts per hour is being released, was detected through an image taken by a gamma camera Sunday. The site was 10 meters above ground and close to where the first record-high level of radiation was detected.

A Packbot–a robot that measures radiation levels–that TEPCO sent to the second floor of the No. 1 reactor building detected a radiation level of 5 sieverts at a third location near the pipe that was used to vent steam from the containment vessel.

Meanwhile, construction has begun around the No. 1 reactor to cover up the building to prevent radioactive substances from spreading.

“It’s highly unlikely that people will go near those locations [where high levels of radiation were detected], and the findings will not affect construction,” said Junichi Matsumoto, acting director of TEPCO’s Nuclear Power and Plant Siting Division.

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N-agency seeks cooling report

The Nuclear and Industrial Safety Agency ordered TEPCO on Tuesday to report whether cooling systems at the Nos. 1 to 3 reactors are working properly and stably.

The agency’s request is a step in the process toward possibly lifting the emergency evacuation preparation zone between 20 and 30 kilometers from the nuclear plant.

After receiving the report from TEPCO, the agency will estimate the amount of radioactive substances released from the reactors to ensure the safety of the zone.

To lift the zone, the nuclear safety agency must confirm that the reactors are stably cooled, so that radioactive material will not spread.

Before assessing the cooling systems, the agency requires TEPCO to report its evaluation of the quake-resistance capacity of the cooling systems and their cooling capacity, as well as measures for restoring them in the event of a power outage or malfunction.

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