TEPCO investigates radiation levels of exhaust stack at Fukushima Daiichi

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Fukushima Daiichi Unit 1 and Unit 2 exhaust stack

Workers at the Fukushima Daiichi nuclear power plant used a camera attached to a long pole with a dosimeter to explore highly radioactive areas near the combined exhaust stack for Unit 1 and Unit 2 reactors.  Part of the decommissioning process requires the reinforcement and dismantling of portions of the exhaust stack, but the contaminated areas make it impossible for workers to access some of the required areas.

The investigation found radiation doses of 95 millisieverts per hour 5 feet from the SGTS piping at the base of the exhaust stack.

Cracks were previously identified in the exhaust stack some 200 feet above the ground during seismic safety evaluations.  Radiation levels inside the pipe were measured at more than 10 Sieverts per hour.

Fukushima Daiichi Unit 1 and Unit 2 exhaust stack

TEPCO assumes that the high dose areas identified by investigations, is likely due to two or more highly radioactive sources in the piping.  It is estimated that the sources may around 25 Sieverts per hour near-surface, with a dose rate of some 15 Sieverts per hour.

The investigation did not determine whether Unit 1 or Unit 2 was the source of the contamination.

Source: TEPCO

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  1. Highest radiation levels measured outside reactor
    Dec. 6, 2013 NHK (Japan Broadcasting Corporation)

    Tokyo Electric says radiation levels are extremely high in an area near a ventilation pipe at the Fukushima plant.

    Tokyo Electric found radiation of 25 sieverts an hour on a duct, which connects reactor buildings and the 120-meter-tall ventilation pipe.

    The estimated radiation level is the highest ever detected outside reactor buildings. People exposed to this level of radiation would die within 20 minutes.

  2. Record radiation levels detected in well at Fukushima nuke plant
    December 14, 2013 ASAHI SHIMBUN(Japan’s newspaper)

    A record 1.8 million becquerels of beta-ray sources per liter of water were detected at a monitoring well at the crippled Fukushima nuclear power plant, operator Tokyo Electric said.

    The reading concerns strontium and other beta-ray sources.

    The water was sampled at a monitoring well in an area close to the sea near the No. 2 reactor building. The well is located close to trenches holding highly radioactive water.

    Tokyo Electric said the reading apparently spiked after highly radioactive water seeped into the surroundings through failed parts of the trenches.

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