| TOKYO, April 18
TOKYO, April 18 Tokyo Electric Power Co
(TEPCO), the operator of the Fukushima Daiichi nuclear power
plant at the centre of Japan's crisis, said on Sunday it hopes
to achieve a "cold shutdown" of its crippled plant within six to
The following summarises what TEPCO aims for and some of the
challenges facing the operator as Japanese engineers scramble to
deal with the worst nuclear crisis since the 1986 Chernobyl
WHAT IS A COLD SHUTDOWN?
A cold shutdown is a state in which the water cooling the
fuel rods is below 100 degrees Celsius and the reactors are
considered stable. It means that the water used to cool the fuel
rods is below boiling point.
Of the Daiichi plant's six reactors hit by the earthquake
and tsunami, two are seen as safe, but the other four remain
Workers succeeded in halting the reactors after the quake
hit, but they were unable to cool them in time before some of
the fuel melted inside the reactor cores after the water cooling
WHY IS TEPCO'S ANNOUNCEMENT SIGNIFICANT?
This is the first time TEPCO announced a timetable for its
operations since the disaster that struck more than five weeks
Within the first three months, the operator said, it plans
to cool the reactors and the spent fuel stored in some of them
to a stable level and reduce the leakage of radiation.
TEPCO then hopes to bring the reactors to a cold shutdown in
another three to six months.
HOW DOES TEPCO INTEND TO ACHIEVE A COLD SHUTDOWN?
The operator said it wants to fill the reactors with enough
water so the fuel rods can be cooled for a cold shutdown.
TEPCO has been pouring water into the reactor vessels, which
contain the nuclear fuel rods, since the disaster to cool the
rods as an emergency measure.
In a step forward from this emergency measure, TEPCO wants
to achieve a cold shutdown by filling the containment vessel, an
outer shell of steel and concrete that houses the reactor
vessel, with water in a step known as water entombment.
At the same time it will work to restore the reactors'
cooling system, which functions like a radiator on an
automobile. TEPCO said mounting a separate cooling system
externally was also a possibility.
For reactors like the No.2 reactor with suspected damage to
the containment vessel, TEPCO said it hopes to seal damaged
sections with a type of cement to prevent water being pumped in
from leaking out.
WHAT ARE THE CHALLENGES FACING TEPCO?
The aim to fill the reactors with enough water sounds simple
but engineers have had to battle with a damaged cooling system
since the earthquake.
Until the cooling systems are fixed or other alternatives
are online to continually cool the reactors, workers will be
forced to keep injecting new water to cool the fuel and create a
steady flow of contaminated water.
Within its self-imposed time frame TEPCO said it will build
storage tanks to store the contaminated water and attempt to
treat some of it. It also aims to cover the reactors with large
covers to prevent the spread of radioactive material into the
TEPCO said constant aftershocks, power outages, high levels
of radiation and the threat of hydrogen explosions were also
factors that could hamper its work.
Weather conditions, such as the approaching rainy season and
typhoons and lightning during the summer, could also pose
WHAT ARE OFFICIALS SAYING?
Banri Kaieda, Japan's trade minister, told reporters on
Sunday: "The first juncture towards safety would be when the
fuel rods are fully submerged in water and a cold shutdown is
"But true safety will not come until the fuel rods are
removed from the reactors," he said, adding that he would like
to assess in six to nine months whether residents evacuated from
near the Daiichi plant can return home.
Hidehiko Nishiyama, a deputy director-general at Japan's
nuclear safety agency, said: "Unlike a normal shutdown when
large quantities of sea water can be used to cool down a
reactor, the options are limited, so it may take a significant
amount of time until a cold shutdown is reached."
(Reporting by Shinichi Saoshiro; Editing by Chris Gallagher)