Fukushima Aftermath/Davis-Besse Nuclear Power Station

Davis-Besse Nuclear Power Station is a nuclear power plant with a single pressurized water reactor, also referred to as a light water reactor. As of 2006, it is operated by the FirstEnergy Nuclear Operating Company subsidiary of FirstEnergy Corp. 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 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. 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.

The Davis-Besse NPP (NRC image)

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.

Unit One

Unit One is an 879 MWe pressurized water reactor supplied 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.

The reactor head under inspection

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.

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 include Toledo (26 miles to city center).

Incident history

Over the years of its operation, the plant has experienced several incidents, none of which have resulted in exposure to dangerous levels of radiation.

First stuck-open pilot-operated relief valve

On September 24, 1977, the reactor, running at only 9% power, shut down because of a disruption in the feedwater system. This caused the relief valve for the pressurizer to stick open. As of 2005, the NRC considers this to be the fourth highest ranked safety incident.

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 "unusual event" (the lowest classification the NRC uses) but it was later determined that it should have been classified a "site area emergency".

Tornado

On June 24, 1998 the station was struck by an F2 tornado. 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.

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

Reactor head hole

In March 2002, plant staff discovered that the boric acid 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 of the carbon steel reactor pressure vessel head over an area roughly the size of a football (see photo). This significant reactor head wastage left only 3/8 inch of stainless steel cladding holding back the high-pressure (~2500 psi) reactor coolant. A breach would have resulted in a loss-of-coolant accident, in which superheated, superpressurized reactor coolant could 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. Under certain scenarios, a reactor rupture would have resulted in core meltdown and/or breach of containment and release of radioactive material. 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. The U.S. Justice Department investigated and penalized the owner of the plant over safety and reporting violations related to the incident. The NRC determined that this incident was the fifth most dangerous nuclear incident in the United States since 1979.

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.

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.

2008 discovery 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

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 cracked 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. 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 is scheduled for replacement in 2011.

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). 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 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. [3]. The site map contains many valuable links

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.

External links

• "Davis-Besse Nuclear Generating Station, Ohio". Energy Information Administration, U.S. Department of Energy (DOE). 2008-10-03. Archived from the original on 2012-05-27. Retrieved 2008-11-19.
• "Davis-Besse Pressurized Water Reactor". Operating Nuclear Power Reactors. U.S. Nuclear Regulatory Commission (NRC). 2008-02-14. Retrieved 2008-11-19.
• [4]
• 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)