|
|
Local
Companies | Article published December 12, 2002
Davis-Besse rust is a mystery
Only test run will show if underside is
leaking
By TOM HENRY
BLADE STAFF
WRITER
The Nuclear Regulatory Commission photographed the area
around one of 52 nozzles being investigated after it was
cleaned by a robot. The area had been covered by rust.
| OAK
HARBOR, Ohio - When Davis-Besse shut down Feb. 16, the focus was on
the nuclear plant’s reactor head. Now, with FirstEnergy Corp. hoping
for a restart in early 2003, attention has shifted to the vessel’s
underbelly.
One of the biggest mysteries looming at the plant
25 miles east of Toledo is whether the bottom of the reactor is
leaking.
Extensive rust was found there in June, but to date
the company has attributed it solely to residue from previous
wash-downs of the reactor head. The theory is that some of the boric
acid that had been rinsed off over the years ended up clinging to
the sides of the vessel and clustering beneath
it.
FirstEnergy officials reiterated their belief Tuesday
that the bottom of the reactor is free of leaks. But one of them,
Bob Schrauder, director of support services, told Nuclear Regulatory
Commission officials there are at least a couple of spots where
concentrations of boron and lithium - two chemicals in the reactor -
are too heavy to support the notion that all the rust came from
wash-downs.
"There were some nozzles that were not in the
flow path,’’ Mr. Schrauder told the NRC, referring to 52 nozzles
implanted in the bottom.
But he also said isotopes found in
samples taken from 12 of those 52 nozzles don’t have a DNA-like
match-up to the stuff inside the reactor.
In other words, Mr.
Schrauder agreed: None of the lab tests or visual inspections to
date can prove beyond a doubt that the bottom of the reactor is
leaking. Or that it isn’t.
The NRC agrees little else can be
done to solve that mystery until the plant is reloaded with nuclear
fuel and is powered up for a real-life test run. That will include
getting the reactor up to its normal 600-degree operating
temperature and pressure of 2,200 pounds per square inch. All
systems would be operating, with one major exception: Control rods
will be fully inserted to keep nuclear fission from
occurring.
The company’s latest timetable calls for that
walk-through exercise in mid February.
In addition to lab
tests and visual inspections, FirstEnergy’s contention is based
largely on a phenomenon that nuclear engineers called stress
corrosion cracking.
A certain type of metal known as Alloy
600 - widely used in America’s fleet of 103 nuclear plants,
especially in thin nozzles implanted at the top and bottom of the
reactor - has been found to be vulnerable to high temperatures and
pressure as its ages.
Davis-Besse is one of seven nuclear
plants designed by the former Babcock & Wilcox Co., all of which
typically operate 10 to 30 degrees hotter than similar
pressurized-water plants. Davis-Besse, which typically operates at
605 degrees, was the nation’s hottest plant prior to its
shutdown.
The bottom of Davis-Besse’s reactor is usually 556
degrees when the plant is in operation, nearly 50 degrees cooler
than the reactor head, in part, because of the natural tendency for
heat to rise. The NRC agrees that drop-off in temperature can be
hugely significant in terms of stress corrosion cracking.
"We
don’t believe there is any leakage. But if there is, we have a
repair concept ready," Jim Powers, the company’s engineering
director, said.
FirstEnergy is equipping the reactor with a
cavity seal as an extra barrier from future wash-down residue, Lew
Myers, chief operating officer, said. Jack Grobe, NRC oversight
panel chairman, said that work is not mandated.
Separate from
the 69 nozzles atop the reactor head, the 52 nozzles on the bottom
are for instruments that give plant operators a peek of what’s going
on inside the reactor. The 69 on top are passageways for moving
equipment linked to control rods used to operate the reactor
safely.
The NRC admittedly had no inkling of a six-inch
cavity in Davis-Besse’s reactor head, apparently caused by reactor
acid that leaked out of those 69 nozzles on the head. It was looking
for microscopic, hairline cracks that might have existed in the
reactor-head nozzles - and instead stumbled upon what officials have
described as the nuclear industry’s biggest near-miss since the
Three Mile Island accident of 1979.
Workers who entered the
plant’s containment building on March 6 found rust had eaten away
all but the thin liner in one part of a six-inch-thick reactor head.
| More articles on this subject » |
|
|
| AP Wall Street News » |
|
| Index |
Last |
Change |
|
| Dow |
8471.97 |
-66.43 |
|
| Nasdaq |
1377.18 |
-22.37 |
|
| S&P 500 |
893.93 |
-7.65 |
|
|
| Quick Quotes
|
|
| |
 |
| |
|
