Antinuclear

Is Fukushima nuclear plant ‘under control’ – in fact, it is in a precarious state

The spent fuel rods stored at the No. 4 reactor pose a particular threat, experts say, because they lie unprotected outside the unit’s containment vessel. Tokyo Electric has been racing to fortify the crumpled outer shell of the reactor, and to keep the tank fed with water. But should a problem also arise with cooling the spent fuel, the plant could run the risk of another colossal radiation leak, experts say.

“The plant is still in a precarious state,” 

Japan Admits Nuclear Plant Still Poses Dangers By HIROKO TABUCHI NYT,  March 29, 2012, TOKYO — The damage to the core of at least one of the meltdown-stricken reactors at Fukushima could be far worse than previously thought, raising fresh concerns over the plant’s stability and gravely complicating the post-disaster cleanup, a recent internal investigation has shown.

The results of the inquiry, released this week by the operator of the Fukushima Daiichi Nuclear Power Plant, also cast doubt over the Japanese government’s declaration three months ago that the ravaged site is now under control.

Throughout the crisis that ensued after a powerful earthquake and
tsunami last March, both the plant’s operator, Tokyo Electric Power,
or Tepco, and the government were accused of playing down the dangers
posed by the nuclear meltdown. Subsequent disclosures that the event
was indeed far more severe than they let on have badly damaged their
credibility, to the point that almost any statement from the
authorities is now regarded as suspect by a dubious Japanese
public……
earlier this week, an examination at one of the reactors showed the
water level at its core to be far lower than levels previously
estimated, raising fears that the broken-down remnants of the uranium
fuel rods there may not be completely submerged and in danger of
heating up again.

Cooling water at the plant’s No.2 reactor came up to just 2 feet from
the bottom of the reactor’s containment vessel, a beaker-shaped
structure that encases the fuel rods. That was far below the 10
meter-level (33 feet) estimated by officials when the government
declared the plant stable in December.

The low water levels also raise concerns that radioactive water may be
leaking out of the reactor at a higher rate than previously thought,
possibly into a part of the reactor known as the suppression chamber,
and into a network of pipes and chambers under the plant — or into the
ocean. At the No. 2 reactor, workers still pump about 9 tons of water
an hour into the core to keep it cool.

The investigation also found current radiation levels of 72.0 Sieverts
inside the containment vessel, enough to kill a person in a matter of
minutes, as well as for electronic equipment to malfunction.
Kazuhiko Kudo, a professor of nuclear engineering at Kyushu University
in southwestern Japan , said it was now suspect whether the nuclear
fuel was being adequately cooled. And if some parts of the fuel
remained above water, there was a risk the fuel could again heat up
and melt. That could trigger a dangerous spike in the pressure inside
the containment vessel, and lead to more radiation escaping the
reactor, he said.

The high levels of radiation would greatly complicate work to locate
and remove the damaged fuel and decommission the plant’s six reactors
— a process that is expected to take decades………
Two other badly-damaged reactors — Nos. 1 and 3 — could be in even
worse condition. Hydrogen explosions blew out the outer walls of those
reactors, and officials believe that more nuclear fuel has breached
the containment vessel at the No. 1 reactor than the others.

Experts also worry about a fourth reactor that was not operating at
the time of the accident, but nevertheless poses a risk because of the
large number of spent nuclear fuel rods stored in a water coolant tank
there. The No. 4 reactor was also hit by a hydrogen explosion in the
early days of the crisis, possibly due to hydrogen that leaked into
the reactor from the adjacent No. 3 unit.

The spent fuel rods stored at the No. 4 reactor pose a particular threat, experts say, because they lie unprotected outside the unit’s containment vessel. Tokyo Electric has been racing to fortify the crumpled outer shell of the reactor, and to keep the tank fed with water. But should a problem also arise with cooling the spent fuel, the plant could run the risk of another colossal radiation leak, experts say.

The many aftershocks that continue to hit the Fukushima region are
also a source of worry.

“The plant is still in a precarious state,” said Mr. Kudo of Kyushu
University. ““Unfortunately, all we can do is to keep pumping water
inside the reactors,” he said, “and hope we don’t have another big
earthquake.” http://www.nytimes.com/2012/03/30/world/asia/japan-admits-nuclear-plant-still-poses-dangers.html

March 30, 2012 - Posted by Christina Macpherson | Uncategorized