Davis-Besse plant

Nearly all major disasters provide ample evidence of the failures of organizations to learn from their own or other organizations experience. In the case of Three Mile Island for example, a similar accident had occurred some months before at the similarly designed Davis Besse plant, but correct worker intervention had averted an accident. 

In the Davis Besse plant in the USA, because of leaks from cracks on the control rod housings, a large corrosion was found (2002) on the head of the pressure vessel, having a depth equal to that of the base metal (only the stainless steel liner was left for the containment of the pressurized water) and plan dimensions of the same order of magnitude. Many mistakes were made in order to arrive at that point ... 

However, after installation of the SPDS at operating plants, the Davis-Besse plant Loss-Of-Feedwater event and other operating plant SPDS availability surveys raised concerns regarding SPDS reliability and availability and its impact on plant safety. 

The one-unit Davis-Besse nuclear power plant is located in Oak Harbor, Ohio. The plant is operated by the Toledo Edison Company. The plant consists of one Babcock Wilcox PWR designed for a maximum operational power of 874 MWe. The Davis-Besse plant has been in operation since July of 1978. Key systems of the Davis-Besse plant are depicted in Figures 2A-1 through 2A-6. 

The following sections describe a loss-of-feedwater incident that occurred at the Davis-Besse plant. In view of the importance of the operator actions in this event, the description is a narrative based upon a composite of the operator interviews performed by an NRC review team following the incident (NUREG-1154). The review team decided that this would best convey the effects of stress, training, experience, teamwork, and impediments on operator performance. 

In the past only two nuclear accidents (Three Mile Island and Chernobyl) were widely reported, while over 100 went unreported. These other accident were not caused by only earthquakes, design errors or terrorist acts, but more recently also by software virus attacks through the Internet. For example, on January 25, 2003 a Slammer worm penetrated the private computer network of Ohio s Davis-Besse nuclear power plant, and stopped its control computer. The only reason a meltdown did not result is because the plant was not in operation. 

The Davis-Besse Nuclear Power Plant on the shore of Lake Erie in Oak Harbor, Ohio. Photograph by Robert J. Huffman. Field... 

Nuclear Reactor with a Hole in the Head On March 6,2002, personnel repairing one of the five cracked control rod drive mechanism (CRDM) nozzles at Davis-Besse Nuclear Plant, Oak Harbor, Ohio, discovered extensive damage to the reactor vessel head. The reactor vessel head is a dome-shaped structure made from carbon steel housing the reactor core. The reactor vessel head is placed such that it can be removed when the reactor is shut down to allow spent nuclear fuel to be replaced with fresh fuel. The CRDM nozzles connect motors mounted on a platform above the reactor vessel head to control rods inside the reactor vessel. Reactor operators withdraw control rods from the reactor core to start the operation of the plant and insert the control rods to shut down the operation of the reactor. 

The reactor core at the Davis-Besse Nuclear Plant sits within a metal pot designed to withstand pressures up to 17 MPa. The reactor vessel has 15-cm thick carbon steel walls and has adequate strength. The water used for cooling the reactor contains boric acid, which is corrosive to carbon steel. Hence, the inner surface of the reactor vessel is covered with a 0.6-mm thick layer of stainless steel. But water routinely leaked on to the reactor vessel s outer surface. 

LONG TERM ACTIONS -DAVIS BESSE EVENT-PLANT SPECIFIC SIMULATOR... 

Organizational structure had similar impacts at Davis-Besse. At the Davis-Besse nuclear power station, management did not follow up to ensure that industry and NRC-mandated surveillances of vessel head integrity were conducted properly. The plant executive... 

On June 9, 1985, the midnight shift of operators assumed control of the Davis-Besse nuclear power plant. The oncoming shift included four licensed operators, four equipment operators, an auxiliary operator, and an administrative assistant. The shift supervisor and the assistant shift supervisor are licensed senior reactor operators and the most experienced members of the operating crew. Both were at the plant before it was issued an operating license in April 1977. The reactor operators, who were responsible for the control room, had decided between themselves who would be responsible for the primary-side and... 

The NRC review team concluded that the underlying cause of the Davis-Besse loss-of-feedwater incident was the licensee s lack of attention to detail in the care of plant equipment. The licensee had a history of performing troubleshooting, maintenance and testing of equipment, and of evaluating operating experience related to equipment in a superficial manner and,... 

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