In order to improve the working environment in the reactor building of
Unit 2, Fukushima Daiichi Nuclear Power Station, we started gradually
opening the airlock of the reactor building from 8:51 pm on June 19 with
care to avoid spreading the dust inside the building, after circulating
the air inside the building for a few days by installing an ambient air
filtration system. Then, at 5:00 am on Jun 20, we had the airlock fully
opened.
Related to this opening of the airlock, we evaluated the influence of
this opening to the instrument reading (the latest level is approximately
several dozen μ Sv/h) of the monitoring posts at the site borders of
the station and confirmed that the influence is not the level that changes
the reading.
We also conducted monitoring with a portable indicator at 3 5 km outside
from the station and confirmed significant increase in the reading at one
of the measured points (Yamada, Futaba Town). Therefore, we checked the
situation of that monitoring and identified the causes which include the
difference of the monitoring points.
The difference between the 2 monitoring data measured at different points
is considered to be resulted from the difference of the surrounding
environment.
(Previously announced since June 8, 2011)
With regard to this issue we received verbal request from Nuclear and
Industrial Safety Agency to reconfirm the validity of monitoring conducted
along with opening the airlock and report the confirmation results and
measures on recurrence prevention if there are any points to be improved.
Accordingly, we compiled and reported the causes and measure on recurrence
prevention to Nuclear and Industrial Safety Agency yesterday.
○Attachment
Regarding the Preventive Measures against the Causes of Incompatibility
of Environmental Monitoring when Opening the Airlock at Fukushima
Daiichi Nuclear Power Station Unit 2 (summary) (PDF 20.6KB)