The Davis-Besse nuclear reac- tor's emergency cooling system has been
flawed since the plant opened 26 years ago and could have failed when
needed most, during a catastrophic coolant leak, according to a new
analysis.
Had the reactor's rust-damaged lid given way, or a major pipe ruptured,
the consequences could have been more serious than experts first thought,
and worse than the plant owner has publicly acknowledged until now.
The report, prepared by FirstEnergy Corp. for the Nuclear Regulatory
Commission in mid-December, says that in an accident, debris could have
choked off the flow of water to the plant's emergency coolant pumps and
water sprays. That equipment - intended to keep the reactor's radioactive
core from melting and to wash radioactive particles from the air inside
the protective containment building - may not have worked properly or at
all in certain conditions.
The company had previously acknowledged the potential sump failure only
in theoretical terms.
"This is a very significant plant deficiency," said Hal Ornstein, a
retired NRC senior safety analyst.
"The plant has essentially been operating from the get-go outside its
design basis."
Ornstein said the report "contains the admission that Davis-Besse would
most probably have melted" if there had been a loss-of-coolant accident.
A potentially disastrous combination existed at the Toledo-area plant,
according to the company's assessment. Structures and equipment in the
reactor building were coated with substandard paint and insulation that
jets of steam from a coolant leak could blast loose.
The resulting debris could clog the screen of the sump in the
containment building, preventing emergency pumps from returning enough
spilled coolant to the hot reactor core.
The sump screen also had a 4.5-square-inch gap that could let larger
rubbish pass through, potentially damaging pump blades or blocking the
nozzles of water sprays that cool and scrub the superheated air.
The flaws did not come to the attention of Davis-Besse managers or the
NRC until the intensive company and government inspections in the wake of
the discovery last March of a pineapple-size rust hole all the way through
the reactor's 6.5-inch steel lid, leaving only a thin liner.
To improve the sump, FirstEnergy is greatly enlarging its size,
removing much of the old insulation and paint, and has promised to further
pin down how likely it would have been for the equipment to become
inoperable.
The NRC is also studying that issue. Both parties, as well as several
people with experience in nuclear plants, say the findings are sobering.
"Things could have gotten real ugly," said David Lochbaum, a nuclear
safety engineer with the Union of Concerned Scientists, who first called
attention to the document.
The emergency equipment "would not have worked as it's designed to
work," said Jim Powers, the engineering director of FirstEnergy's nuclear
division. "There's a lot of unknowns and questions. There was a potential
the sump could be blocked," although debris from a lid rupture would have
to escape a gantry around the top of the reactor and follow a "torturous
path" past obstacles to reach the sump's screened cover.
"It's not a situation you want to get into, and we didn't," said
Powers, pointing out that the steel liner beneath the rust-ravaged lid did
not give way.
The company's preliminary estimate is that the cracked and slightly
bulging liner was about two years from rupture when workers stumbled upon
the rust hole.
In the early minutes after a significant loss-of-coolant accident -
what the industry calls a LOCA - hundreds of thousands of gallons of
chemical-laced water are pumped into the leaking reactor to replace the
coolant spilling out. Davis-Besse has a 400,000-gallon storage tank, but
its supply would be exhausted in about 25 minutes.
At that point, the reactor's operators must switch to the emergency
sump to pump coolant from the floor of the containment building back into
the hemorrhaging reactor. A wire-mesh strainer 14 feet long, 5 feet wide
and 2 feet high covers the sump. If more than 50 percent of that strainer
is blocked, the pumps will not get enough water flow to properly cool the
core.
If the radioactive fuel rods in the core get too hot, they can melt,
releasing steam and explosive hydrogen and threatening the integrity of
the heavily shielded containment building. In America's worst nuclear
accident to date, at Three-Mile Island, the core partially melted but only
very small amounts of radiation escaped the containment building.
Although the NRC has studied the sump-clogging issue for at least a
decade, the agency has not written regulations requiring plants like
Davis-Besse with high-pressure reactors to change the design of their
sumps. FirstEnergy has previously said it voluntarily decided to radically
enlarge its sump area - by 3,000 percent - in order to be an industry
leader, not because of design flaws.
The NRC "would need a staff the size of the Department of Homeland
Security" to inspect every inch of every reactor, said Bill Dean, vice
chairman of the panel overseeing Davis-Besse's repair. Instead, the agency
must depend on reactor operators to catch and report issues it deems to be
of lower significance.
FirstEnergy, formed by a merger in 1997, did not exist when Davis-Besse
was built. "I don't know why this wasn't identified earlier on,"
FirstEnergy's Powers said, "but the nuclear industry's sensitivity has
increased over the years" to the issue of sump clogging and improper
paints and insulation.
Still, nuclear engineer and whistleblower Paul Blanch is amazed the
Davis-Besse flaws weren't caught sooner. "It's incredible. Had the
microscope not been focused on them [FirstEnergy], they would have gone on
forever."
Since Davis-Besse must seek NRC permission to restart the plant, the
agency will inspect to make sure the company's fixes are adequate, Dean
said. A fine is not likely, since the agency must prove that rule
violations were deliberate.
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