Simulation Shows Deeper
Meltdown At Tsunami-Hit Japan Nuclear Reactor Than
Fukushima Power Plant
EMF Protection Devices
Magnetic Field Detector
TOKYO — Radioactive debris
from melted fuel rods may have seeped deeper into the floor
of a Japan’s tsunami-hit nuclear reactor than previously
thought, to within a foot from breaching the crucial steel
barrier, a new simulation showed Wednesday.
The findings will not change
the ongoing efforts to stabilize the reactors more than
eight months after the
Fukushima Dai-ichi plant was disabled, but they harshly
depict the meltdowns that occurred and conditions within the
reactors, which will be off-limits for years.
The plant operator Tokyo Electric Power Co. said its latest
simulation showed fuel at the No. 1 reactor may have eroded
part of the primary containment vessel’s thick concrete
floor. The vessel is a beaker-shaped steel container, set
into the floor. A concrete foundation below that is the last
manmade barrier before earth.
The fuel came within a foot of the container’s steel bottom in the
worst-case scenario but has been somewhat cooled, TEPCO’s
nuclear safety official Yoshihiro Oyama said at a government
workshop. He said fuel rods in the No. 1 reactor were the
worst damaged because it lost cooling capacity before the
other two reactors, leaving its rods dry and overheated for
hours before water was pumped in.
The nuclear crisis following the March 11 earthquake and tsunami
caused massive radiation leaks and the relocation of some
Another simulation on the structure released by the
government-funded Japan Nuclear Energy Safety Organization,
or JNES, said the erosion of the concrete could be deeper
and the possibility of structural damage to the reactor’s
foundation needs to be studied.
JNES official Masanori Naito said the melting fuel rods lost their
shape as they collapsed to the bottom of the vessel, then
deteriorated into drops when water pumping resumed, and the
fuel drops spattered and smashed against the concrete as
they fell, Naito said.
TEPCO and government officials are aiming to achieve “cold
shutdown” by the end of the year — a first step toward
creating a stable enough environment for work to proceed on
removing the reactors’ nuclear fuel and closing the plant
The government estimates it will take 30 years or more to safely
decommission Fukushima Dai-ichi.
Wednesday’s simulations depict what happened early in the crisis
and do not mean a recent deterioration of the No. 1 reactor.
Oyama said, however, the results are based only on available
data and may not match the actual conditions inside the
reactors, which cannot be opened for years.
Some experts have raised questions about achieving the “cold
shutdown,” which means bringing the temperature of the
pressure vessel containing healthy fuel rods to way below
the benchmark 100 Celsius (212 Fahrenheit). They say the
fuel is no longer there and measuring the temperature of
empty cores is meaningless, while nobody knows where and how
hot the melted fuel really is.
Kiyoharu Abe, a nuclear expert at JNES, said it’s too early to make
a conclusion and more simulations should be done to get
“I don’t think the simulation today was wrong, but we should look
at this from various viewpoints rather than making a
conclusion from one simulation,” Abe said. “It’s just the
beginning of a long process.”