Further cracking found at Davis-Besse

Inspections have identified three previously undetected cracks in the concrete shield building of the Davis-Besse nuclear power plant in Ohio, as well as some growth in cracks discovered in 2011. These are not considered to effect the plant's safety.

Inspections have identified three previously undetected cracks in the concrete shield building of the Davis-Besse nuclear power plant in Ohio, as well as some growth in cracks discovered in 2011. These are not considered to effect the plant's safety.

Davis-Besse (Image: Fenoc)

Plant operator First Energy Nuclear Operating Company (Fenoc) discovered "tight cracks" within the reinforced concrete of the Davis-Besse reactor building in October 2011 during a major outage to replace the head of the reactor pressure vessel. The company notified the Nuclear Regulatory Commission (NRC), which determined the cracks did not present an "immediate safety issue" and the reactor returned to service two months later.

Examination of the inside of the building's walls is currently being conducted using high-definition camera technology through a series of inspection ports. So far, inspections have been carried out through 43 of the shield building's 82 inspection ports. The remaining examinations are expected to be completed over the next several weeks.

The current inspections have identified three "very tight, subsurface pre-existing cracks" in the building that were not visible with previous inspection technology. The inspections have also found that three other cracks, discovered in October 2011, "appear to have propagated a small amount."

Vice president of the Davis-Besse site Ray Lieb stressed, "Analysis of all inspection results to date confirms the 2011 conclusion that the shield building's structural integrity is not impacted by the presence of these tight cracks. The robust building continues to function safely and reliably."

Weather-induced

Following the initial discovery of the cracks, Fenoc concluded that they had been caused by a severe blizzard in January 1978. Davis-Besse's shield building has since been equipped with a weather-proof coating.

The 30-inch (76.2 cm) thick shield building surrounds a 1.5-inch (3.8 cm) thick steel containment vessel that contains the reactor system. The two structures are separated by a 54-inch (137.1 cm) space and both have important roles in nuclear safety: The sealed containment vessel is a final safety barrier to contain radioactivity in the event of an accident while the shield building protects this from external forces.

Fenoc has a licence to operate Davis-Besse's 908 MWe pressurized water reactor until 2017, but it has applied for a licence extension to 2037.

Researched and written
by World Nuclear News