Davis-Besse Nuclear Power Station is a nuclear power plant with a single reactor located on the southwest shore of Lake Erie near Oak Harbor, Ohio. It is the 57th commercial power reactor to commence building in the United States of America (construction began on September 1, 1970) and the 50th to come on-line.[1] The plant was originally jointly owned by Cleveland Electric Illuminating (CEI) and Toledo Edison (TE). As of 2006, it is operated by the FirstEnergy Nuclear Operating Company subsidiary of FirstEnergy Corp. The plant was named for former TE Chairman John K. Davis and former CEI Chairman Ralph M. Besse.
According to the Nuclear Regulatory Commission, Davis-Besse has been the source of two of the top five most dangerous nuclear incidents in the United States since 1979.[2]
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[edit]Unit One
Unit One is an 873 MWe pressurized water reactorsupplied by Babcock and Wilcox. The reactor was shut down from 2002 until early 2004 for safety repairs and upgrades, so recent operational statistics are not yet available for the unit.
[edit]Incident history
Over the years of its operation, the plant has experienced several significant safety-related incidents. The U.S. Justice Department also investigated and penalized the owner of the plant over safety and reporting violations related to a March 2002 incident.
[edit]First stuck-open pilot-operated relief valve
On September 24, 1977, a potentially serious incident was initiated when the reactor, running at only 9% power, "tripped" (shut down) because of a disruption in the feedwater system.[3] The half-trip of the steam and feedwater rupture control system initiated closure of the startup feedwater valve. This valve feeds water into the steam generator, and so this event resulted in reduced water level in Steam Generator 2. The pressurizer pilot-operated relief valve (PORV) lifted nine times and then stuck open because of rapid cycling. (ref NRC LER 346/77-016) As of 2005, the NRC considers this to be the third (excluding the accident at TMI) highest ranked incident most likely to have resulted in a nuclear disaster in the event of a subsequent failure. [4]
[edit]Loss of feedwater event
On June 9, 1985, the two main feedwater pumps, used to supply water to the nuclear reactor steam generators, shut down. One pump tripped on an overspeed condition due to a pump turbine control system electronic failure. The second pump tripped on a momentary high discharge pressure signal caused by the second pump attempting to make up for the flow lost by the tripping of the first pump. A control room operator then attempted to start the auxiliary (emergency) feedwater pumps. These pumps both tripped on overspeed conditions because the operator had pushed the incorrect buttons during the start attempt. This incident was originally classified an "unusual event" (the lowest classification the NRC uses for an incident) but it was later determined that it should have been classified as a "site area emergency".[5] As of 2005, the NRC considers this to be the fifth (excluding TMI) highest ranking incident most likely to have resulted in a nuclear disaster in the event of a subsequent failure.[4]
[edit]Tornado
On June 24, 1998 the station was "directly hit" by an F2 tornado. [6] The plant's switchyard was damaged and access to external power was disabled. Also damaged by the tornado was the roof of the Turbine building and the roof the of the administrative building, the latter having extensive flood damage to the second floor. The plant's reactor automatically shut down at 8:43 pm and an alert (the next to lowest of four levels of severity) was declared at 9:18 pm. The plant's emergency diesel generators powered critical facility safety systems until external power could be restored.[7][8]
[edit]Reactor head hole
In March 2002, after the government had allowed a delay in safety inspections past a December 31, 2001 deadline, it was discovered that boric acid had eaten almost all the way through the 6½-inch thick reactor pressure vessel head. A breach might have partially flooded the reactor's containment building with reactor coolant, and resulted in emergency safety procedures to protect from core damage. In 2005 the NRC ranked this occurrence as the 10th (excluding TMI) most likely incident to have led to a nuclear disaster in the event of a subsequent failure.[4]
The resulting corrective maintenance took two years, during which time further material problems were corrected to bring the reactor back online safely. Repairs and upgrades cost $600 million, and the Davis-Besse reactor was restarted in March 2004. Follow up action by the NRC on the March 2002 incident occurred on April 21, 2005, when the NRC issued a Notice of Violation and Proposed Imposition of Civil Penalties in the amount of $5,450,000 for multiple violations including the degradation of the reactor pressure vessel head.[9]
On January 20, 2006, the owner of Davis-Besse, FirstEnergy Corporation of Akron, Ohio, acknowledged a series of safety violations by former workers, and entered into a deferred prosecution agreement with the US Department of Justice. The deferred prosecution agreement relates to the March 2002 incident (see above). The deferment granted by the NRC were based on letters from Davis-Besse engineers stating that previous inspections were adequate. However, those inspections were not as thorough as the company suggested, and as proved by the material deficiency discovered later. In any case, because FirstEnergy cooperated with investigators on the matter, they were able to avoid more serious penalties. Therefore, the company agreed to pay fines of $23.7 million, with an additional $4.3 million to be contributed to various groups, including the National Park Service, the US Fish and Wildlife Service,Habitat for Humanity, and the University of Toledo as well as to pay some costs related to the federal investigation. In addition, two former employees and one former contractor were indicted for statements made in multiple documents and one videotape, over several years, for hiding evidence that the reactor pressure vessel was being corroded by boric acid. The maximum penalty for the three is 25 years in prison. The indictment mentions that other employees also provided false information to inspectors, but does not name them.[10]
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