At Fukushima Daiichi Nuclear Power Station, we are working on the
stabilization of the reactor of Unit 1 by continuing the nitrogen gas
injection to the reactor containment vessel and adjusting the water
injection rate to the reactor monitoring several parameters.
In order to solidify these efforts, we need to install and calibrate a new
reactor water level gauge. Also, we need to install a circulating cooling
system to improve the status of the reactor to a more stable cooled
condition. To do so, we have to improve the working environment inside the
reactor building.

At this moment, in preparation for the improvement, we are conducting the
visual inspection and measuring the radiation dose and the density of
radioactive substances by a remote controlled robot inside the reactor
building. From now on, we will install an ambient air filtration system*,
circulate air inside the reactor building for a while, filter the
radioactive substances and lower the density. After that, in order for
workers to enter the reactor building and conduct necessary works, we will
open the airlock. Before opening the airlock, we will monitor the density
of the radioactive substances within the reactor building and confirm that
the influence to the outside is low enough.
We will announce beforehand in opening the airlock of the reactor building.
At the same time, we will closely monitor figures at monitoring posts and
announce these.

* Ambient air filtration system
This system vacuums up the ambient air at the work area by a fan, filters
impurities and cleans the air. 

Appendix: Filtering the air by an ambient air filtration system (Unit 1) 
                                                              (PDF 61.3KB)