Equipment designed to prevent a hydrogen gas explosion similar to
what happened during the Three Mile Island partial nuclear meltdown
has been inoperable at FirstEnergy Corp.'sDavis-Besse plant since it
opened in 1977, a report shows.
For all those years, Davis-Besse technicians had followed
procedures to turn knobs on the equipment that indicated interior
valves were working, but the valves actually had frozen closed.
Davis-Besse workers discovered the broken equipment during a
safety systems check in early May, according to the report given to
the Nuclear Regulatory Commission. The Union of Concerned Scientists
on Tuesday released copies of the report, which was filed June 30
with the NRC.
The broken equipment is the latest in a long list of other safety
problems discovered at the troubled plant in Oak Harbor, about 25
miles east of Toledo.
FirstEnergy said backup systems likely would have detected a
hydrogen gas buildup if there was a major accident inside the
containment chamber, warding off the likelihood of an interior
explosion. The massive concrete and steel containment chamber is the
last line of defense between a malfunctioning or damaged reactor and
The Akron utility will permanently replace the faulty valves with
open piping, spokesman Todd Schneider said. The problem should not
slow downFirstEnergy's efforts to get the plant ready to restart by
the end of summer, he said.
The Davis-Besse ``licensee event report'' said valves that allow
containment gas analyzers to detect a hydrogen gas buildup inside
the containment chamber ``have been in the closed position since
plant startup in 1977.''
The stuck valves were found after tests May 2 showed that there
was no flow of gas through a device called a heat exchanger,
according to the NRC document. The exchanger is part of a system
designed to control the amount of hydrogen released during what is
called a loss of coolant accident, where the nuclear reactor coolant
spills into the containment chamber.
Davis-Besse workers over the years conducted monthly tests that
involved turning the knobs that controlled the valves; but while the
knobs turned, the interior parts of the valve did not, Schneider
``They (plant workers) were following procedures to make sure the
valves were open,'' he said. ``It appeared to be working
The Nuclear Regulatory Commission will look into the matter,
spokesman Jan Strasma said.
It does not appear that the stuck valves is an industrywide
issue, he said.
``It would appear to be a plant-specific-type problem,'' he
Davis-Besse and NRC inspectors are conducting thorough reviews of
the plant's safety systems, Strasma said.
David Lochbaum, the Union of Concerned Scientists' nuclear
expert, said in an e-mail that when nuclear fuel overheats, hydrogen
is created when moist air interacts with the nuclear fuel rods. The
containment gas analyzer is supposed to alert plant staff about
hydrogen gas buildup so they can take action.
At Three Mile Island, large amounts of hydrogen were created when
the Pennsylvania plants' nuclear fuel overheated on March 28, 1979,
Lochbaum said. About 10 hours after the accident started, the
hydrogen blew up inside the containment chamber, causing the
interior pressure to jump from about three pounds per square inch to
28 pounds per square inch, he said. That's the equivalent of putting
36 tons of pressure on a containment door that is 3 feet by 6 feet,
But even after Three Mile Island, Davis-Besse's malfunctioning
hydrogen gas-detecting equipment went undiscovered.
Schneider said in the unlikely event of a loss-of-coolant
accident, Davis-Besse workers had other means to detect a hydrogen
buildup and deal with it.
If hydrogen gas builds up, workers can pump air inside the
containment chamber to dilute it, he said. A fall-back option is to
purge the hydrogen gas through filters into the environment, he
Davis-Besse has been kept shut down ever since a large corrosion
hole was found in March 2002 nearly all the way through the reactor
vessel head that covers the nuclear fuel. The damage will cost
FirstEnergy hundreds of millions of dollars and has sparked
technical and criminal investigations.
In September, Davis-Besse workers found that the plant's former
sump strainer system, designed to keep the nuclear fuel from melting
during a loss-of-coolant accident, may have been faulty ever since
the plant was built and made the plant more susceptible to a
worst-case meltdown. FirstEnergy since has spent about $2.3 million
to build a state-of-the-art sump.