When the earthquake happened,
the reactor 1, 2 and 3
were shut down automatically.
Unit 4, 5 and 6 were shut
down previously for outages,
with unit 4 having been defueled
in November 2010. So
chain reaction was stopped
within seconds of the earthquake
but the uranium fuel
rods remained very hot.
It is called decay heat and
it takes 20 -24 hours to cool
down the reactor to less than
212 Celsius and achieve the
state, which is called cold
shutdown. Emergency power
generators supplied power
for the cooling system due
to the loss of offsite power as
they designed to do. Things
were moving smoothly.
With the earthquake, the tsunami
warning was issued and
they expected a 10 ft tsunami.
Fukushima Daiichi was
situated 30 ft above sea level
and nobody cared about the
tsunami. When the tsunami
struck the power plant,
the waves were massive and
they were more than 50 ft
high. Both emergency power
generators were affected,
but there were another 2
emergency generators. Both
generators were not affected
but both of them had their
switches in the basement and
both basements were affected
by the tsunami. So, both generators
were unusable.
A few minutes later, the entire
alarming system went off and
station blackout happened.
That means, all the AC and
DC power sources of the power
plant were not working.
Now there’s nothing to stop
the meltdown. The people
in the control room had no
clue that the reactors contain
the water or not. If the water
in the nuclear reactor was
boiled and evaporated, then
the fuel rods will start to melt.
Engineers collected batteries
from vehicles and tried to
power on the alarm system.
But, since there was no way to
stop the meltdown, the Japanese
government declared an
emergency at the Fukushima
Daiichi power plant.
On Saturday, 12th march
around 6:22 pm, the first hydrogen
explosion happened
on the service floor of the
building above unit 1 reactor
containment and injured four
people. Around 8:20 pm, residents
living within 20 kilometers
of the plant were told
to evacuate the area. Around
200,000 people had to leave.
On 14th March the second
explosion happened in the
reactor no 2 and authorities
began to pump a mixture of
seawater and boron into the
No.2 reactor to cool its nuclear
fuel rods. Early on the 14th,
the third hydrogen explosion
happened in the reactor no 3
as well, but surprisingly, reactor
no 4 also caught fire. This
one was shut down before
the tsunami and the earthquake.
This explosion happened
from hydrogen arising
in unit 3 and reaching unit 4
by backflow in shared ducts
when vented from unit 3.
The peak of radioactive release
was reported on the 15th
and apparently from the explosion
of the reactor no 2. To
take the reactors into the cold
shutdown conditions, they
had to pump water and nitrogen
until December 2012.
GAUGE Magazine
University of Peradeniya
Page
41