Davis Besse (USA)

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900 MW PWR constructed by BW, operation since 1977.

Facilities in Davis Besse

plantreactor typconstruction startoperation startshut down
Davis Besse-1PWR19701977
Jury: Worker covered up damage at Ohio nuke plant 

TOLEDO, Ohio: Jurors on Tuesday convicted a former nuclear plant engineer of hiding information from government regulators about the worst corrosion ever found at a U.S. reactor.
Prosecutors said Andrew Siemaszko and two other workers lied in 2001 so the Davis-Besse plant along Lake Erie could delay a shutdown for a safety inspection. Months later, inspectors found  an acid leak that nearly ate through the reactor's 6-inch-thick steel cap.
Siemaszko covered up the damage to the plant's reactor vessel head and lied to the Nuclear Regulatory Commission, the federal jury said.
It's not clear how close the plant, was to an accident.
Siemaszko faces up to five years in prison and $250,000 in fines. He was convicted on three of five counts, including concealing material information from the government. The jury cleared him
on two counts of making false statements.
Following the discovery of the leak, the NRC beefed up inspections and training and began requiring detailed records of its discussions with plant operators.
Siemaszko's attorneys said the plant's owner set him up as a scapegoat because he spoke out about safety concerns. They will consider an appeal.
"I'm disappointed," Siemaszko said. When asked what message. the verdict sends, he said: "Do not go against a big company."
Siemaszko was responsible for making sure the reactor vessel head was cleaned and inspected. He said he was wrongly fired and that he had told supervisors the reactor needed to be cleaned. He said managers rejected his requests.
Defense attorney Billie Pirner Garde said nuclear workers will be less likely to raise concerns about safety. "This makes the nuclear industry less safe," she said.
The plant's operator, Akron-based FirstEnergy Corp., said Siemaszko deserved to be fired and should have caught the damage.
FirstEnergy paid a record $28 million in fines a year ago while avoiding federal charges. It also spent $600 million making repairs and buying replacement power while the plant was closed from early 2002 until 2004.
None of the company's senior leaders was charged in the investigation.
Another former worker at the Davis-Besse plant was sentence to three years' probation in May for concealing information from the government. A private contractor was acquitted.

Worst corrosion ever found in a US-reactor vessel

On 6 March 2002, workers discovered significant corrosion in the carbon steel reactor
vessel head at the Davis-Besse pressurized water reactor in Oak Harbor, Ohio. The head is
bolted onto the reactor pressure vessel containing the reactor core during operation. There are
sixty-nine holes in the head that allow control rods inside the reactor vessel to be connected to
their external motors. There are stainless steel tubes, called control rod drive mechanism
nozzles, through each hole and welded to the stainless steel inner liner of the head. It is
believed that one of these tubes developed a crack around 1991. By 1996, the crack extended
all the way through the metal wall of the control rod drive mechanism nozzle and began
leaking borated reactor coolant water. The leak rate was small, less than 1 gallon per minute,
but it persisted for nearly 6 years.
When the leaked water evaporated, it left behind dry boric acid crystals. Boric acid is
very corrosive to carbon steel. It began eating through the carbon steel head to expose the stainless steel liner.
The liner was not intended to be pressure-retaining, but for years it was the
only barrier preventing a loss of coolant accident. As boric acid widened the hole, the stress
loading of the liner increased. A government study estimated that the hole would have
widened to the point where the liner ruptured in another 2 to 11 months of operation by
Davis-Besse. Because Davis-Besse ran 18 months between refueling outages, had the damage
been missed during the 2002 outage, it seems likely that a loss of coolant accident would have
Had the 5mm stainless steel liner ruptured, a hole with a diameter of approximately
250mm would have created a medium-sized loss of coolant accident. While Davis-Besse was
equipped with emergency systems to mitigate such an accident, these backup systems were
also found to be impaired.
(source: Risidual Risk May 2007)
The NRC calculated the severe core damage risk from this event to be 6 x 10-3 or 0.6% per reactor year and rated it INES Level 3.


Plant was forced shut 147 hours by switchyard and grid damage initiated by a tornado and lightening storm.


Utility published revised estimates for decommissioning costs: 1987: 122 million US$
1993: 347 million US$
Annual contribution to decommissioning fond is 1,3 million US$.
The study performed by TLG Services assumes removal of all structures from the site and a 5 year minimum cooling period for spent fuel - without cooling the cost decrease to 318 million.


MFW flow oscillations caused power fluctuations and scram on intermediate high flux.