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Regional News
| Article published Friday, May 9, 2003
NRC curious about ‘unique’ cracks at
Davis-Besse
By MICHAEL WOODS
BLADE SCIENCE
EDITOR
ROCKVILLE, MD. - Hairline cracks penetrated
through all but two-tenths of an inch of a metal sheet that shielded
northwest Ohio from a potentially serious nuclear accident, a U.S.
Nuclear Regulatory Commission official said yesterday.
That’s
about the thickness of three credit cards.
New tests on the
cracks at the Davis-Besse Nuclear Power Station have left experts
with a mystery to solve because they appear highly
unusual.
"Most curious," William H. Cullen, Jr., remarked
after a meeting of the Advisory Committee on Reactor Safeguards. The
expert panel is NRC’s in-house safety board.
"Most curious.
You ask how unique? The uniqueness is absolute. Nobody in the
research world has ever seen this before."
Experts expected
that all of the cracks would be of different depths, Mr. Cullen
said. But they all were about the same depth, each leaving
two-tenths of an inch of intact metal.
The cracks first
raised eyebrows when detected last year in stainless steel
"cladding" that lined the inner surface of the original Davis-Besse
reactor vessel head.
FirstEnergy, which owns Davis-Besse, has
replaced the damaged component as part of preparations for
restarting the plant.
It has been shut down since February,
2002, because of a leak of corrosive water that rusted a
4-inch-by-5-inch hole through the vessel, which holds nuclear fuel.
The infamous rust hole incident has led to a nationwide tightening
of safety procedures at other nuclear plants.
The vessel’s
6.5-inch-thick walls hold back radioactive water pressurized to
2,250 pounds per square inch. The hole put that burden on the liner,
which averaged just 0.25 inches in thickness and was not designed as
a pressure-resistant safety shield.
It held, but had begun to
bulge and crack under the strain.
Had the liner burst, a
serious release of radioactivity could have occurred, Mr. Cullen
pointed out. Radioactive water traveling through the hole would have
contaminated Davis-Besse.
In addition, water loss could have
led to the most serious kind of nuclear power plant accident,
risking widespread release of radiation from the reactor.
Mr.
Cullen said that experts at FirstEnergy contractor Framatome ANP, in
Lynchburg, Va., now have measured and analyzed cracks in the bulging
liner. Among the goals is to determine exactly how close it was to
the bursting point.
Experts may have an explanation for the
unusual cracking pattern by summer, when the analysis is complete,
he said.
By then NRC also expects to finish calculating how
close the cladding was to a rupture and a release of radioactive
material.
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