PORT CLINTON - The Davis-Besse nuclear power
plant for decades had a cooling system flaw that, under a worst-case
scenario, could have led to a meltdown of the fuel core, plant owner
FirstEnergy has told the Nuclear Regulatory Commission.
The flaw, a wider-than-allowed gap in a sump strainer system, was
discovered last September during an inspection by FirstEnergy and
reported to the NRC in December. That gap could have allowed debris
created during what is called a loss-of-coolant accident to clog an
emergency cooling system, rendering it inoperable, the Akron
utility's report to the NRC said.
FirstEnergy is spending $2.3 million to replace the old sump
system with a larger, state-of-the-art system.
Because of the upgrade, the discovery of the flaw, while not
trivial, is not an issue for the plant's restart, said Jack Grobe,
an NRC official who heads an oversight panel looking into the
troubled Oak Harbor power plant. He and other NRC officials met with
FirstEnergy managers Tuesday at Camp Perry as part of a series of
regular monthly meetings to get updates on progress being made to
repair and refurbish Davis-Besse. The plant has been closed for
nearly a year after the discovery that boric acid ate unprecedented
cavities on top of the reactor's former vessel head.
The flaw in the old sump system, a ¾-inch-wide-by-6-inch- long
gap, was apparently part of the plant's original construction in the
1970s, the FirstEnergy report said. Subsequent inspections of the
sump system focused on the grating and did not require close looks
at the area where the flaw was, the report said.
``This procedure did not explicitly require inspection to ensure
all design bases functions were met,'' the report said.
``For some reason it was not noticed,'' said Jim Powers, director
of nuclear engineering at Davis-Besse. Powers, who pushed to have
the Davis-Besse sump system redesigned so that it is state of the
art for the industry, previously put through sump system
improvements at FirstEnergy's Perry nuclear plant.
Grobe said the NRC's inspections focus more on a nuclear
reactor's moving parts rather than static safety components such as
the sump grating. The flaw in the old Davis-Besse sump does not
indicate there is also a flaw in the NRC's inspections, he said.
Sump system safety has been an issue for years in the nuclear
power industry, Grobe and others said. The NRC plans to send out a
draft regulatory guide in a month about improving sump system
requirements. The sumps are intended to recirculate coolant back to
the fuel core to prevent a meltdown. If debris caused by the
explosive release of steam and coolant from the reactor clogs the
sump, the system cannot recirculate the coolant. That in turn could
cause the fuel to overheat and begin melting.
The NRC's analysis of the sump system flaw indicates a core
meltdown would have been unlikely if the boric acid cavities on top
of the old reactor head had burst and released coolant, Grobe said.
But if there had been an accident that released a larger amount of
coolant, the old sump design may not have been sufficient to protect
the reactor, he said.
The 68 other reactors in the United States that are similar in
design to Davis-Besse must at least evaluate the sump problem, said
David Lochbaum, nuclear expert with the Union of Concerned
In related news, FirstEnergy executives said they may begin
reloading nuclear fuel as soon as today into Davis-Besse as part of
preparations to test the bottom of the reactor for coolant leaks in