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)