13 Aug (NucNet): The Tokyo Electric Power Company (Tepco) is investigating the cause of an alarm indicating a high radiation dose rate at the continuous dust monitor in front of the main anti-earthquake building at Fukushima-Daiichi nuclear power plant on 12 August.
The alarm went off at approximately 12:30 PM local time and an instruction was given for all personnel to put on full-face or half-face masks while the status of the radiation levels was confirmed using a portable dust monitor.
The result of the dust measurement in front of the building showed 14 becquerels per cubic metre (Bq/m3) and later 12 Bq/m3 total beta activity. This was below the recommended value for the use of full-face masks at Fukushima-Daiichi (200 Bq/m3).
Tepco also says the heads and faces of ten people waiting for a bus in front of the main anti-earthquake building showed high levels of surface contamination (up to 19 becquerels per square centimetre – 19 Bq/cm2) upon being tested at the entrance control building. Their bodies were wiped and their contamination level was confirmed to be below the internal operation management value of 4 Bq/cm2.
It was presumed that the contamination of the personnel could have originated from the mist generator, which sprays water mist in front of the main anti-earthquake building to clean the air and prevent stroke by reducing the air temperature.
Tepco says the use of water in the building was prohibited at approximately 13:15 and a measurement of possible contamination was conducted. Samples were taken from the water supply of the main anti-earthquake building, the mist generator, the entrance control building and the purification plant.
The results showed levels of gamma and beta radiation below the detection limit – less than 3 becquerels per litre (Bq/ℓ) for Cesium-134 and -137 and less than 13 Bq/ℓ for total beta radioactivity.
Tepco considers the cause of the incident to be a “localised surge of dust in front of the main anti-earthquake building” and will continue to investigate other possibilities.
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To contact the editor responsible for this story: Lubomir Mitev at lubomir.mitev@nucnet.org
