Davis–Besse Nuclear Power Station

Davis–Besse Nuclear Power Station
The Davis–Besse NPP (NRC image).
Location of Davis–Besse Nuclear Power Station in Ohio
Country	United States
Location	Carroll Township, Ottawa County, near Oak Harbor, Ohio
Coordinates	41°35′48″N 83°5′11″W / 41.59667°N 83.08639°W / 41.59667; -83.08639Coordinates: 41°35′48″N 83°5′11″W / 41.59667°N 83.08639°W / 41.59667; -83.08639
Status	Operational
Construction began	1970
Commission date	July 31, 1978
Owner(s)	Cleveland Electric (51.4%) Toledo Edison (48.6%)
Operator(s)	FirstEnergy Nuclear
Nuclear power station
Reactor type	pressurized water reactor
Reactor supplier	Babcock & Wilcox
Power generation
Units operational	1 × 889 MW
Make and model	Babcock & Wilcox
Nameplate capacity	889 MW
Average generation	7,706 GWh

Davis–Besse Nuclear Power Station's cooling tower in July 2015

Davis–Besse Nuclear Power Station is a nuclear power plant northeast of Oak Harbor in Ottawa County, Ohio, United States. It has a single pressurized water reactor. As of 2011, it is operated by the FirstEnergy Nuclear Operating Company subsidiary of FirstEnergy Corp.

On March 5, 2002, maintenance workers discovered that corrosion had eaten a football-sized hole into the reactor vessel head of the Davis–Besse plant. Although the corrosion did not lead to an accident, this was considered to be a serious nuclear safety incident.^[1][2] The Nuclear Regulatory Commission kept Davis–Besse shut down until March 2004, so that FirstEnergy was able to perform all the necessary maintenance for safe operations. The NRC imposed its largest fine ever—more than $5 million—against FirstEnergy for the actions that led to the corrosion. The company paid an additional $28 million in fines under a settlement with the U.S. Department of Justice.^[1]

According to the NRC, Davis–Besse has been the source of two of the top five most dangerous nuclear incidents in the United States since 1979.^[3]

Location and history

The power station is located on the southwest shore of Lake Erie about 10 miles (16 km) north of Oak Harbor, Ohio and is on the north side of Highway 2 just east of Highway 19 on a 954-acre (386 ha) site in the Carroll Township. The plant only utilizes 221 acres (89 ha), with 733 acres (297 ha) devoted to the Ottawa National Wildlife Refuge. The entrance to the Magee Marsh Wildlife Area^[4] is less than a mile east of the power station. The official name according to the U.S. Energy Information Administration is the Davis–Besse Nuclear Generating Station. 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 July 31, 1978.^[5] The plant was originally jointly owned by Cleveland Electric Illuminating (CEI) and Toledo Edison (TE) and was named for former TE Chairman John K. Davis and former CEI Chairman Ralph M. Besse.

Unit One

The reactor head under inspection

Unit One is an 879 MWe pressurized water reactor supplied by Babcock & Wilcox. The reactor was shut down from 2002 until early 2004 for safety repairs and upgrades. In 2012 the reactor supplied 7101.700 GWh of electricity^[6]

Incident history

1977 first stuck-open pilot-operated relief valve

On September 24, 1977, the relief valve for the reactor pressurizer failed to close when the reactor, running at only 9% power, shut down because of a disruption in the feedwater system.^[7] As of 2005, the NRC considers this to be the fourth highest ranked safety incident.^[8] Despite this incident, a (undiagnosed) stuck-open relief valve played an important role in the later Three Mile Island accident. ^[9][10]

1985 loss of feedwater event

On June 9, 1985, the main feedwater pumps, used to supply water to the reactor steam generators, shut down. A control room operator then attempted to start the auxiliary (emergency) feedwater pumps. These pumps both tripped on overspeed conditions because of operator error. This incident was originally classified an "NRC Unusual Event" (the lowest classification the NRC uses) but it was later determined that it should have been classified a "site area emergency".^[11]

1998 tornado

On June 24, 1998 the station was struck by an F2 tornado.^[12] The plant's switchyard was damaged and access to external power was disabled. 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.^[13][14]

2002 reactor head hole

Erosion of the 6-inch-thick (150 mm) carbon steel reactor head, caused by a persistent leak of borated water

In March 2002, plant staff discovered that the borated water that serves as the reactor coolant had leaked from cracked control rod drive mechanisms directly above the reactor and eaten through more than six inches^[15] (150 mm) of the carbon steel reactor pressure vessel head over an area roughly the size of a football (see photo). This significant reactor head wastage on the interior of the reactor vessel head left only ³⁄₈ inch (9.5 mm) of stainless steel cladding holding back the high-pressure (~2500 psi, 17 MPa) reactor coolant. A breach most likely would have resulted in a massive loss-of-coolant accident, in which reactor coolant would have jetted into the reactor's containment building and resulted in emergency safety procedures to protect from core damage or meltdown. Because of the location of the reactor head damage, such a jet of reactor coolant might have damaged adjacent control rod drive mechanisms, hampering or preventing reactor shut-down. As part of the system reviews following the accident, significant safety issues were identified with other critical plant components, including the following:

1. the containment sump that allows the reactor coolant to be reclaimed and reinjected into the reactor;
2. the high pressure injection pumps that would reinject such reclaimed reactor coolant;
3. the emergency diesel generator system;
4. the containment air coolers that would remove heat from the containment building;
5. reactor coolant isolation valves; and
6. the plant's electrical distribution system.^[16]

The resulting corrective operational and system reviews and engineering changes took two years. Repairs and upgrades cost $600 million, and the Davis–Besse reactor was restarted in March 2004.^[17]

The U.S. Department of Justice (DoJ) investigated and penalized the owner of the plant over safety and reporting violations related to the incident. The company paid $28 million in fines under a settlement with the DoJ.^[1] The NRC determined that this incident was the fifth-most dangerous nuclear incident in the United States since 1979,^[3] and imposed its largest fine ever — more than $5 million — against FirstEnergy for the actions that led to the corrosion.^[1]

During the period when the corrosion was taking place undetected, Davis-Besse accumulated 5 million worker-hours without a lost-time accident. "Employees and managers at Davis-Besse have achieved this and other milestones by paying close attention to detail and striving for excellence in even minor daily activities. Because of this operating philosophy, Davis-Besse has been recognized within the nuclear industry as a top performing plant" ^[18]

2003 slammer worm

In January 2003, the plant's private network became infected with the slammer worm, which resulted in a five-hour loss of safety monitoring at the plant ^[19][20]

2006 criminal prosecutions

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 U.S. 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 U.S. Fish and Wildlife Service, Habitat for Humanity, and the University of Toledo as well as to pay some costs related to the federal investigation.^[21]

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.^[21][22]

2008 discovery of tritium leak

The NRC and Ohio EPA were notified of a tritium leak accidentally discovered during an unrelated fire inspection on October 22, 2008. Preliminary indications suggest radioactive water did not infiltrate groundwater outside plant boundaries.^[23]

2010 replacement reactor head problems

After the 2002 incident, Davis–Besse purchased a used replacement head from a mothballed reactor in Midland, Michigan. Davis–Besse operators replaced the original corroded reactor head before restarting in 2004. On March 12, 2010, during a scheduled refueling outage, ultrasonic examinations performed on the control rod drive mechanism nozzles penetrating the reactor vessel closure head identified that two of the nozzles inspected did not meet acceptance criteria. FirstEnergy investigators subsequently found new cracks in 24 of 69 nozzles, including one serious enough to leak boric acid. Root cause analysis is currently underway by the Department of Energy, First Energy, and the NRC to determine the cause of the premature failures.^[24][25] Crack indications required repair prior to returning the vessel head to service. Control rod drive nozzles were repaired using techniques proven at other nuclear facilities. The plant resumed operation in 2010. The existing reactor vessel head was scheduled for replacement in 2011.^[26]

2011 shield building cracks

An October 2011 shutdown of the plant for maintenance revealed a 30 foot long hairline crack in the concrete shield building around the containment vessel.^[27]

2012 reactor coolant pump seal pinhole leak

On June 6, 2012, an approximately 0.1 gpm pinhole spray leakage was identified from a weld in a seal of the reactor coolant pump during a routine reactor coolant system walkdown inspection. The plant entered limited operations, and root cause analysis was undertaken.^[28]

2015 steam leak shutdown

On May 9, 2015, a steam leak in the turbine building caused FirstEnergy operators to declare an 'Unusual Event' and shut the reactor down until repairs could be made.^[29] The plant was brought back online and synchronized with the local power grid at 11:11pm on Tuesday May 12 after repairs were completed.^[30]

Future

The facility's original nuclear operating license expires on April 22, 2017. On August 11, 2006 FirstEnergy Nuclear Operating Company (FENOC) submitted a letter of intent (Adams Accession No. ML062290261).^[31] The submission date for the application is August 10, 2010. This initiates a long process that results in an application approval or revocation. Public hearings^[32] are a vital part of any application review and information on this process can be found on the U.S. Nuclear Regulatory Commission (NRC) website at NRC.gov. .

Seismic risk

The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Davis–Besse was 1 in 149,254, according to an NRC study published in August 2010.^[33][34]

Surrounding population

The Nuclear Regulatory Commission defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of 10 miles (16 km), concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about 50 miles (80 km), concerned primarily with ingestion of food and liquid contaminated by radioactivity.^[35]

The 2010 U.S. population within 10 miles (16 km) of Davis–Besse was 18,635, an increase of 14.2 percent in a decade, according to an analysis of U.S. Census data for msnbc.com. The 2010 U.S. population within 50 miles (80 km) was 1,791,856, an increase of 1.4 percent since 2000. Cities within 50 miles (80 km) include Sandusky, Ohio, 22 miles (35 km); Toledo, Ohio 26 miles (42 km); and Detroit, Michigan, 50 miles (80 km) (distance to the city centers).^[36] U.S. Census data for Canadian population within the area is not available, though Leamington, Ontario is 39 miles (63 km) away, and Windsor, Ontario (population: 230,000) is 49 miles (79 km) from Davis–Besse.

The cooling tower for Davis–Besse stands at 493 feet above the surrounding area, making it a major landmark around the western end of Lake Erie. The tower is visible from the Michigan shore and on clear days the water vapor plume can be seen from Bowling Green, Ohio, over 40 miles away.

See also

• Nuclear reactor accidents in the United States
• Pilot-operated relief valve

References

External links

• Davis–Besse Pressurized Water Reactor Information from the U.S. Nuclear Regulatory Commission
• Union of Concerned Scientists report on Davis–Besse
• U.S. Nuclear Regulatory Commission's "Davis–Besse Lessons Learned Task Force" (with links to the Task Force Report)