Only $2.51 for this heartwarming family classic. No DVD
collection is complete without 'Born Free'. OUR DEAL: 87% off!
http://pd.gophercentral.com/u/1103/c/186/a/3289
------------------------------------------------------------
THE PROGRESSIVE REVIEW - April 7, 2011
U.S. Sees Array of New Threats at Japan's Nuclear Plant
by: James Glanz and William J. Broad
The New York Times
United States government engineers sent to help with the
crisis in Japan are warning that the troubled nuclear plant
there is facing a wide array of fresh threats that could
persist indefinitely, and that in some cases are expected
to increase as a result of the very measures being taken
to keep the plant stable, according to a confidential
assessment prepared by the Nuclear Regulatory Commission.
Among the new threats that were cited in the assessment,
dated March 26, are the mounting stresses placed on the
containment structures as they fill with radioactive cool-
ing water, making them more vulnerable to rupture in one
of the aftershocks rattling the site after the earthquake
and tsunami of March 11. The document also cites the
possibility of explosions inside the containment structures
due to the release of hydrogen and oxygen from seawater
pumped into the reactors, and offers new details on how
semimolten fuel rods and salt buildup are impeding the
flow of fresh water meant to cool the nuclear cores.
In recent days, workers have grappled with several side
effects of the emergency measures taken to keep nuclear
fuel at the plant from overheating, including leaks of
radioactive water at the site and radiation burns to
workers who step into the water. The assessment, as well
as interviews with officials familiar with it, points to
a new panoply of complex challenges that water creates
for the safety of workers and the recovery and long-term
stability of the reactors.
While the assessment does not speculate on the likelihood
of new explosions or damage from an aftershock, either
could lead to a breach of the containment structures in
one or more of the crippled reactors, the last barriers
that prevent a much more serious release of radiation from
the nuclear core. If the fuel continues to heat and melt
because of ineffective cooling, some nuclear experts say,
that could also leave a radioactive mass that could stay
molten for an extended period.
The document, which was obtained by The New York Times,
provides a more detailed technical assessment than
Japanese officials have provided of the conundrum facing
the Japanese as they struggle to prevent more fuel from
melting at the Fukushima Daiichi plant. But it appears
to rely largely on data shared with American experts by
the Japanese.
Among other problems, the document raises new questions
about whether pouring water on nuclear fuel in the
absence of functioning cooling systems can be sustained
indefinitely. Experts have said the Japanese need to
continue to keep the fuel cool for many months until the
plant can be stabilized, but there is growing awareness
that the risks of pumping water on the fuel present a
whole new category of challenges that the nuclear industry
is only beginning to comprehend.
The document also suggests that fragments or particles of
nuclear fuel from spent fuel pools above the reactors were
blown "up to one mile from the units," and that pieces
of highly radioactive material fell between two units and
had to be "bulldozed over," presumably to protect workers
at the site. The ejection of nuclear material, which may
have occurred during one of the earlier hydrogen
explosions, may indicate more extensive damage to the
extremely radioactive pools than previously disclosed.
David A. Lochbaum, a nuclear engineer who worked on the
kinds of General Electric reactors used in Japan and
now directs the nuclear safety project at the Union of
Concerned Scientists, said that the welter of problems
revealed in the document at three separate reactors
made a successful outcome even more uncertain.
"I thought they were, not out of the woods, but at least
at the edge of the woods," said Mr. Lochbaum, who was not
involved in preparing the document. "This paints a very
different picture, and suggests that things are a lot
worse. They could still have more damage in a big way if
some of these things don't work out for them."
The steps recommended by the nuclear commission include
injecting nitrogen, an inert gas, into the containment
structures in an attempt to purge them of hydrogen and
oxygen, which could combine to produce explosions. On
Wednesday, the Tokyo Electric Power Company, which owns
the plant, said it was preparing to take such a step and
to inject nitrogen into one of the reactor containment
vessels.
The document also recommends that engineers continue add-
ing boron to cooling water to help prevent the cores from
restarting the nuclear reaction, a process known as
criticality.
Even so, the engineers who prepared the document do not
believe that a resumption of criticality is an immediate
likelihood, Neil Wilmshurst, vice president of the nuclear
sector at the Electric Power Research Institute, said
when contacted about the document. ?I have seen no data
to suggest that there is criticality ongoing,? said Mr.
Wilmshurst, who was involved in the assessment.
The document was prepared for the commission's Reactor
Safety Team, which is assisting the Japanese government
and the Tokyo Electric Power Company. It says it is based
on the "most recent available data" from numerous Japanese
and American organizations, including the electric power
company, the Japan Atomic Industrial Forum, the United
States Department of Energy, General Electric and the
Electric Power Research Institute, an independent, non-
profit group.
------------------------------------------------------------
YOUR VIDEO SNACK BAR
Top Viewed Videos...
1. Creepy or Cool. You decide!
http://c.gophercentral.com/tquc
2. What a Wonderful World It Would Be
http://c.gophercentral.com/Vs03
3. Alfred Hitchcock Montage
http://c.gophercentral.com/xKfb
4. Charlie Sheen - Two and a Half Men
http://c.gophercentral.com/FEle
5. A Cat with A Drinking Problem?
http://c.gophercentral.com/pidK
6. Larry David vs. Vacuum Packaging Check out t
http://c.gophercentral.com/5XUq
------------------------------------------------------------
The document contains detailed assessments of each of the
plant's six reactors along with recommendations for action.
Nuclear experts familiar with the assessment said that it
was regularly updated but that over all, the March 26
version closely reflected current thinking.
The assessment provides graphic new detail on the
conditions of the damaged cores in reactors 1, 2 and 3.
Because slumping fuel and salt from seawater that had
been used as a coolant is probably blocking circulation
pathways, the water flow in No. 1 "is severely restricted
and likely blocked." Inside the core itself, "there is
likely no water level," the assessment says, adding that
as a result, "it is difficult to determine how much cooling
is getting to the fuel." Similar problems exist in No. 2
and No. 3, although the blockage is probably less severe,
the assessment says.
Some of the salt may have been washed away in the past
week with the switch from seawater to fresh water cooling,
nuclear experts said.
A rise in the water level of the containment structures
has often been depicted as a possible way to immerse and
cool the fuel. The assessment, however, warns that "when
flooding containment, consider the implications of water
weight on seismic capability of containment."
Experts in nuclear plant design say that this warning
refers to the enormous stress put on the containment
structures by the rising water. The more water in the
structures, the more easily a large aftershock could
rupture one of them.
Margaret Harding, a former reactor designer for General
Electric, warned of aftershocks and said, "If I were in
the Japanese's shoes, I'd be very reluctant to have tons
and tons of water sitting in a containment whose structural
integrity hasn't been checked since the earthquake."
The N.R.C. document also expressed concern about the
potential for a "hazardous atmosphere" in the concrete-
and-steel containment structures because of the release
of hydrogen and oxygen from the seawater in a highly
radioactive environment.
Hydrogen explosions in the first few days of the disaster
heavily damaged several reactor buildings and in one case
may have damaged a containment structure. That hydrogen
was produced by a mechanism involving the metal cladding
of the nuclear fuel. The document urged that Japanese
operators restore the ability to purge the structures of
these gases and fill them with stable nitrogen gas, a
capability lost after the quake and tsunami.
Nuclear experts say that radiation from the core of a
reactor can split water molecules in two, releasing
hydrogen. Mr. Wilmshurst said that since the March 26
document, engineers had calculated that the amount of
hydrogen produced would be small. But Jay A. LaVerne,
a physicist at Notre Dame, said that at least near the
fuel rods, some hydrogen would in fact be produced, and
could react with oxygen. "If so," Mr. LaVerne said in
an interview, "you have an explosive mixture being
formed near the fuel rods."
Nuclear engineers have warned in recent days that the
pools outside the containment buildings that hold spent
fuel rods could pose an even greater danger than the
melted reactor cores. The pools, which sit atop the
reactor buildings and are meant to keep spent fuel
submerged in water, have lost their cooling systems.
The N.R.C. report suggests that the fuel pool of the
No. 4 reactor suffered a hydrogen explosion early in the
Japanese crisis and could have shed much radioactive
material into the environment, what it calls "a major
source term release."
Experts worry about the fuel pools because explosions
have torn away their roofs and exposed their radioactive
contents. By contrast, reactors have strong containment
vessels that stand a better chance of bottling up radiation
from a meltdown of the fuel in the reactor core.
"Even the best juggler in the world can get too many balls
up in the air," Mr. Lochbaum said of the multiplicity of
problems at the plant. "They've got a lot of nasty things
to negotiate in the future, and one missed step could make
the situation much, much worse."
Henry Fountain contributed reporting from New York,
and Matthew L. Wald from Washington.
------------------------------------------------------------
Follow Your Favorite GopherCentral Publications on Twitter:
http://www.gophertweets.com/ More Coming Soon!
------------------------------------------------------------