of the failed systems to cool the cores.
Figure 2 shows the four damaged
reactors: numbers 1 to 4 going left to
right, and numbers 5 and 6 further to
Reactor 1 experienced a hydrogen
explosion that afternoon. Two days
later, reactor 3 exploded, blowing off
the containment structure’s roof.
Another day later, reactor 4 blew.
Officials were watching reactor 2,
thinking it was okay, but it was later
found that this reactor was leaking
radioactive water into the water table,
causing the most contamination and
damage to the whole area.
Though no direct radiation deaths
have been reported, over 18,000
people have died or are missing from
the events of that fateful day. Children
are still being found to have thyroid
cancer as a result of the events.
The Fukushima disaster scenario
was not as bad as the Chernobyl
reactor explosion in Ukraine in 1986
that made land within 18 miles of that
site uninhabitable for humans. Of
course, they will be able to move back
in 20,000 years. Unfortunately, due to
the massive size of the heavily-damaged reactor building, few robots
were used other than for basic visual
analysis of the damage.
Their solution was to build a huge
sliding concrete dome shown in
Figure 3 next to the reactor where
radiation was much lower, and then
slide it into place over the old
sarcophagus covering the damaged
fourth reactor. Though there were two
medium-sized towns in the Chernobyl
area that had to be permanently
abandoned, there was not the large
population density of almost two
million in the greater Fukushima
Robots Can Operate
Where Humans Can’t
The main difference in a nuclear
reactor disaster and almost any other
emergency situation is the extreme
danger of the high radiation present in
the environment — especially if the
reactors are heavily damaged. There is
no type of protective suit that a human
can wear that can guard them from
the very high radiation levels present
from an exposed reactor’s core.
This leaves the clean-up personnel
with two solutions: leave the reactor
as-is and possibly cover it with a shell
like the Chernobyl solution, or use
robots to do the work.
Water — that later became highly
radioactive — was used to cool the
Fukushima Daiichi reactors and is now
stored in several large tanks in the area.
Many of the tanks began to leak into
the ground water. In 2013, TEPCO
came up with the idea to install an ice
surrounding ground circulating sub-zero
coolant, a frozen soil wall was formed.
Unfortunately, it was soon discovered
to be leaking radioactive ground water.
Typhoons and resulting heavy rains
filled the reactor buildings, causing
heavy water pressure that overcame
the protective frozen soil walls.
Bring in the Robots
Japan has been a world leader in
robotics, and their large industries
immediately went to work designing
specialized robots to assist in the initial
task of cleanup to the damaged
structures. The US company, iRobot
immediately sent several of their
PackBots to help in the operations at
the beginning of the cleanup. The
Honda High-Access Survey Robot was
quickly designed and built to visually
inspect damage not easily seen by
tracked robots on the floor. The
Hitachi ASTACO SoRa dual-armed
tracked robot and the Mitsubishi MHI-Super Giraffe that has an extendable
arm capable of reaching up to 26 ft
were others that offered visual access
in the hard-to-see areas.
Bring in the Robots,
Three years ago, I covered the
early disaster recovery operations at
the Fukushima Daiichi site utilizing
some of the robots mentioned above.
It seemed at the time that disaster
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Advances in robots and robotics over the years.
SERVO 05.2017 61
Figure 2. Heavily damaged reactors at Fukushima.
Figure 3. Concrete safety dome slid over heavily
damaged reactor in Chernobyl, Ukraine.