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NuclearPlantJournal.com Nuclear Plant Journal, May-June 2015
amount of groundwater ingress as well as
preventing the leakage of contaminated
water into the sea.
2.
Provide an overview of the important
activities at the Fukushima Daiichi
nuclear power plant.
As for Unit 1, the reactor building
cover that was put in place back in
October 2011 to minimize the dispersion
of airborne radioactivity, will be carefully
dismantled in order to clean up the rubble
from the refueling floor and prepare for
the fuel removal from the spent fuel pool
in the future.
As part of various approaches to
obtain information on the location of
core debris, muon tomography has been
implemented. Muon is an elementary
particle with a negative electric charge and
is created by cosmic rays showering onto
the earth. Muon tomography is similar to
X-ray imaging but can be applied in areas
that require deeper penetration compared
to X-ray.
We have set up muon detectors near
the Unit 1 reactor building and started
gathering data from February 2015.
Preliminary results obtained by the end
of March 2015 implied that there may not
be much fuel remaining in the core region
of the RPV.
Visual image, temperature data, and
dose rate data inside the drywell have
been successfully obtained by inserting
transforming-type robots inside the
drywell inApril 2015. These findings will
be used to plan for and develop robots for
follow-up investigation near the bottom
of the drywell, where core debris may be
located.
In Unit 2, robots have been used
to investigate inside the torus room,
including the outer surface of the torus,
and water is suspected to be leaking at
a location near the bottom of the torus,
although we have not yet been able to
confirm the exact location. A plan to
insert a robot inside the drywell and
the pedestal to investigate the condition
in the area is underway with a target of
summer of 2015.
In Unit 3, a robot found water leaking
form the drywell into the reactor building
in the main steam line isolation valve
room, located at the 1st level of the reactor
building in May 2014. This is consistent
with the estimated depth of water in the
drywell of about 6 meters (19.68 feet)
from the bottom of the drywell. Drywell
investigation using robots is also planned
for Unit 3 sometime in the fall of 2015,
but the depth of water in the drywell
will pose unique challenges, including
constraints in available penetrations in
the drywell that can be used as entry
points for the robots.
Removing rubble from the spent
fuel pool that fell into the pool due to
the hydrogen explosion of the reactor
building is underway, using remote-
operated cranes and manipulators as dose
rate at the refueling floor is still high.
As for Unit 4, we constructed a
defueling structure covering part of
the reactor building in 2013 and have
successfully removed all of the 1500+
fuels (both new and spent fuels) from the
spent fuel pool in December 2014 without
any significant event. Sample inspection
of spent fuels removed from the Unit 4
spent fuel pool showed no abnormal
conditions,
including
oxidization
thickness.
3.
What is TEPCO doing to gain
public’s confidence?
TEPCO’s announcement in February
2015 with regard to rainwater in the “K”
drainage channel with relatively high
contamination levels that was discharged
to the sea has led to public criticism on
TEPCO’s information disclosure policy.
In light of this event, TEPCO announced
on March 30, 2015 the following new
information disclosure principles:
Overview of water management strategies.
Fukushima
Daiichi...
