OAK HARBOR, Ohio - No additional damage was found yesterday at FirstEnergy Corp.'s Davis-Besse nuclear plant.
As of late afternoon, the number of control-rod drive mechanism nozzles with suspicious flaws remained at 13, Todd Schneider, utility spokesman, said.
Four have cracks, at least two of which were believed to have been leaking.
The nozzles in question are metal sleeves, or passageways, for equipment linked to control rods that shut down or restart the plant's nuclear reactor. Sixty-nine are implanted on top of the reactor head.
The rods are filled with boron; when inserted into the reactor core, the boron stops the fission process, which halts the reactor.
Preliminary inspections have been completed on 66 of the reactor head's 69 nozzles. Results on the final three are expected today, Mr. Schneider said.
Once that initial round of ultrasonic screening is completed, he said, each of the metal tubes that are cracked or flawed will undergo additional testing to see if they have axial, or vertical, cracks.
After that, the utility will use ultrasonic equipment to check them for cracks that are circular in shape. Known as circumferential cracks, they follow a 360-degree pattern and are considered dangerous because they make nuclear reactors more susceptible to releasing radioactive steam. Circumferential cracks compromise the integrity of the nozzles so much that the nozzles can pop off like champagne corks when a plant is operating.
FirstEnergy expects to know by Monday afternoon or evening how many of Davis-Besse's reactor-head nozzles are cracked or otherwise damaged. A repair plan is to be submitted to the U.S. Nuclear Regulatory Commission, which has beefed up its on-site inspection team.
The repairs are to be done by AREVA, a company based in France that was formerly known as Framatome.
The NRC had nothing new to say about the incident yesterday.
Once FirstEnergy knows how many nozzles are cracked and the type of damage that needs to be repaired, it will be in a better position to know approximately how much longer its restart will be delayed, Mr. Schneider said.
Davis-Besse has been down for normal refueling and maintenance since Feb. 28. Those outages typically last four to six weeks.
Nuclear reactors are refueled once every 18 months to two years, depending on the type of uranium in their fuel. During those outages, thousands of inspections and repairs are done - many cannot be performed while a plant is in service.
The plant's latest problem is similar, albeit on a smaller scale, to one eight years ago in which the plant's original reactor head nearly burst and allowed radioactive steam to form. In that case, inspectors found evidence of the problem being overlooked or concealed for at least six years, allowing acid to puddle up beneath insulation and stay constantly moist while the reactor was operating. When the reactor shuts down, it cools off and crystallizes acid on top of it into popcorn-shaped residue.
Davis-Besse was allowed to resume operation in 2004 after a record two-year outage. It has performed safely since then, according to NRC inspectors.
The discovery of trace amounts of residue near two nozzles - characterized by NRC spokesman Vicktoria Mitlyng as about a teaspoon's worth - suggests the latest problem was caught early.
The damage occurred to a replacement head from the mothballed Midland 2 nuclear plant, part of a twin-reactor complex that Consumers Power, the predecessor of Consumers Energy, halted construction on in 1985 because of cost overruns and licensing issues.
The head, built in 1975, was made from an inferior type of alloy that is being phased out in the nuclear industry. FirstEnergy and the NRC expected the metal, though not the preferred alloy, to last much longer before breaking down.
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