Fukushima Daiichi NPS Prompt Report 2013

This is follow-up information regarding the alarm indicating the high-high radioactivity level, which went off at the continuous dust monitor installed in front of the Main Anti-earthquake Building at Fukushima Daiichi NPS today (on August 19).

Amount of two continuous dust monitors installed in front of the Main Anti-earthquake Building was below the high alarming radiation levels. In response, we conducted dust sampling with a portable measurement device from 4:09 to 4:29 PM and found the density of Cesium-137 (8.9 x 10^-6 [Bq/cm³]) was below the level requiring mask (2.0 x 10^-4 [Bq/cm³]).

As part of the subsequent investigation, we conducted dust sampling from 12:48 to 1:08 PM and from 1:50 to 2:10 PM at the east of Unit 1, 2 switching station, which locates on the windward side of the Main Anti-earthquake Building when the incident occurred, and Cesium-134 and Cesium-137 was detected.
- From 12:48 to 1:08 PM
Cesium-134: 3.2 x 10^-5 [Bq/cm³]
Cesium-137: 7.2 x 10^-5 [Bq/cm³]

- From 1:50 to 2:10 PM
Cesium-134: 8.0 x 10^-6 [Bq/cm³]
Cesium-137: 2.1 x 10^-5 [Bq/cm³]

In addition, no significant fluctuation has been found on the amount of monitoring post-2, which locates on the leeward of the Main Anti-earthquake Building. However, increase of indication below the range of the normal monitoring digits was found, as measurement range was widened 1,000 times in order to perform more detailed inspection.
- From 10:00 to 10:20 AM
Increase of 42 / 1000 [μSv/h]
- From 1:30 to 1:50 PM
Increase of 31 / 1000 [μSv/h]
* Normal monitoring digit is two significant figures of μSv/h.

Further, the results of dust sampling with a portable measurement device at monitoring post-2 from 7:55 to 8:25 AM are as follows.
Cesium-134: 3.1 x 10^-7 [Bq/cm³]
Cesium-137: 4.5 x 10^-7 [Bq/cm³]

The instruction to put on masks in the areas not requiring full-face (or half-face) masks in the power station site has been kept in force.