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<DIV class=timestamp>From: <EM>The New York Times</EM></DIV>
<DIV class=timestamp> </DIV>
<DIV class=timestamp>April 5, 2011</DIV>
<DIV class=kicker></DIV>
<H1><NYT_HEADLINE type=" " version="1.0">U.S. Sees Array of New Threats at
Japan’s Nuclear Plant</NYT_HEADLINE></H1><NYT_BYLINE>
<H6 class=byline>By <A class=meta-per title="More Articles by James Glanz"
href="http://topics.nytimes.com/top/reference/timestopics/people/g/james_glanz/index.html?inline=nyt-per">JAMES
GLANZ</A> and <A class=meta-per title="More Articles by William J. Broad"
href="http://topics.nytimes.com/top/reference/timestopics/people/b/william_j_broad/index.html?inline=nyt-per">WILLIAM
J. BROAD</A></H6></NYT_BYLINE><NYT_TEXT>
<DIV id=articleBody><NYT_CORRECTION_TOP></NYT_CORRECTION_TOP>
<P>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 <A class=meta-org
title="More articles about Nuclear Regulatory Commission"
href="http://topics.nytimes.com/top/reference/timestopics/organizations/n/nuclear_regulatory_commission/index.html?inline=nyt-org">Nuclear
Regulatory Commission</A>. </P>
<P>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 cooling 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.
</P>
<P>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. </P>
<P>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. </P>
<P>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. </P>
<P>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. </P>
<P>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. </P>
<P>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 <A class=meta-org title="More articles about Union of Concerned Scientists"
href="http://topics.nytimes.com/top/reference/timestopics/organizations/u/union_of_concerned_scientists/index.html?inline=nyt-org">Union
of Concerned Scientists</A>, said that the welter of problems revealed in the
document at three separate reactors made a successful outcome even more
uncertain. </P>
<P>“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.” </P>
<P>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 <A title="Times article"
href="http://www.nytimes.com/2011/04/07/world/asia/07japan.html">to inject
nitrogen into one of the reactor containment vessels</A>. </P>
<P>The document also recommends that engineers continue adding boron to cooling
water to help prevent the cores from restarting the nuclear reaction, a process
known as criticality. </P>
<P>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.
</P>
<P>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 <A class=meta-org
title="More articles about the U.S. Energy Department."
href="http://topics.nytimes.com/top/reference/timestopics/organizations/e/energy_department/index.html?inline=nyt-org">United
States Department of Energy</A>, General Electric and the Electric Power
Research Institute, an independent, nonprofit group. </P>
<P>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. </P>
<P>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. </P>
<P>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. </P>
<P>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.” </P>
<P>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.
</P>
<P>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.” </P>
<P>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. </P>
<P>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. </P>
<P>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.” </P>
<P>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. </P>
<P>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.” </P>
<P>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. </P>
<P>“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.” </P><NYT_AUTHOR_ID>
<DIV class=authorIdentification>
<P></P>
<P>Henry Fountain contributed reporting from New York, and Matthew L. Wald from
Washington.</P>
<P></P></DIV></NYT_AUTHOR_ID><NYT_CORRECTION_BOTTOM>
<DIV
class=articleCorrection></DIV></NYT_CORRECTION_BOTTOM><NYT_UPDATE_BOTTOM></NYT_UPDATE_BOTTOM></DIV></NYT_TEXT><BR>
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