Fukushima Daiichi NPS Prompt Report 2013

This is a follow-up report on the statuses of an alarm indicating high radiation dose went off at the continuous dust monitor installed in front of the Main Anti-earthquake Building at Fukushima Daiichi Nuclear Power Station today (On August 12).

The result of dust measurement performed in front of the Main Anti-earthquake Building (sampled from 1:05 PM to 1:25 PM) was found to be 1.4 x 10^-5Bq/cm³ (all β).

After that, dust measurement was performed again in front of the Main Anti-earthquake Building (sampled from 2:10 PM to 2:30 PM), and the result was 1.2 x 10^-5Bq/cm³ (all β). In addition, indicated value of continuous dust monitors installed in front of the Main Anti-earthquake Building was 1.1 x 10^-5Bq/cm³, which was sufficiently below the full-face mask wearing standard at Fukushima Daiichi NPS^*1 (2.0 x 10^-4Bq/cm³). Therefore, the instruction that had been given to put on full-face (half face) mask in the areas not requiring full-face mask in the power station site was retracted at 4:17 PM on the same day.

Since wiping of the contaminated bodies of 10 people was conducted, and the contamination level was confirmed to be below the internal operation management value^*2 (4Bq/cm²), they leaved the Entrance Control Building at 2:13 PM on the same day. As a result of the whole body counter testing, no internal radiation was detected.

As a result of the radioactivity analysis (Cs-134, Cs-137) of water for the mist generator and water which was used in the toilet of the 1st floor of the Main Anti-earthquake Building, in the washroom of the 2nd floor of the Entrance Control Building and in the purification plant, the amount was below the detection limit value (approx. 3 x 10^-3Bq/cm³) and confirmed to be sufficiently below the standard value prescribed in the guideline regarding radioactive materials in the bathing area (approx. 1.0 x 10^-2Bq/cm³). Also, all β measurement result was below the detection limit value (approx. 1.3×10^-2Bq/cm³), so the instruction that had been given to prohibit the use of water for hand washing, etc. was retracted at 4:45 PM on the same day.

No significant change has been found on the monitoring post data or the indicated value of the portable continuous dust monitor, which was installed at the south side of the Main Anti-earthquake Building, after the alarm went off.
Therefore, we consider the cause of the incident to be localized surge of the dust in front of the Main Anti-earthquake Building. We will investigate the cause.

*1: One-tenth amount of the standard value specified by the law (2.0 x 10^-3Bq/cm³)
*2: One-tenth amount of the screening level