The lack of exterior weatherproofing when the Davis-Besse nuclear plant was built in 1973, combined with the renowned blizzard of 1978, is the cause of cracks found in portions of a shield building more than 30 years later, FirstEnergy Nuclear Operating Co. said in a report to federal regulators on Tuesday.

FirstEnergy discovered the cracks in the shield building while conducting work last fall to replace the reactor vessel head.

In a 119-page report to the U.S. Nuclear Regulatory Commission, the company said a comprehensive review has indicated that “the absence of exterior weatherproof coating on the Shield Building allowed moisture associated with the blizzard of January 1978 to migrate into the concrete, freeze and expand, causing tight, subsurface cracks in portions of the building. The root cause report concludes that the cracking occurred following the blizzard’s combination of extreme weather conditions, which included three days of driving rain preceding a drastic temperature drop to around 0-degrees Fahrenheit and intense winds through the storm.”

The NRC said it has begun its review of the report and will hold a public meeting and issue a report when its review is complete.

In separate news, parent company FirstEnergy Corp. reported an increase in fourth-quarter earnings and 2011 year-end earnings after the market closed Tuesday in anticipation of its yearly meeting with analysts in New York City this morning.

FirstEnergy Nuclear Operating Co. spokeswoman Jennifer Young said the corrective action for the cracks is to weatherproof the building, or paint it, this summer. Young said weatherproofing was not part of the original specifications of the plant when it was built.

The company also said a team of experts has outlined other actions, including performing additional inspections to verify the cracks have not spread and developing a long-term building monitoring plan. The company said testing and analysis have supported that the concrete in the building is sound and in good condition.

The plant has been operational since early December, when it was given the go-ahead to restart from the NRC.

U.S. Rep. Dennis Kucinich, D-Lakewood, has criticized the restarting of the plant, saying it was premature before a more full investigation could take place. Opponents, including a group called Beyond Nuclear, are also opposing Davis-Besse’s relicensing application.

Asked how the cracks could not have been noticed for 33 years, Young said the cracks were below the surface and not visible from the external part of the building. In 2002, when part of the building was cut open to replace the original reactor head, no cracks were found at that time. When a different part of the building was cut open for the newest reactor head in the fall, cracks were discovered then, she said.

Young said the company did an extensive evaluation using ultrasonic testing and discovered more cracks before the restart. The company believes it has a good idea of where the cracks are, she said.

In its financial report for the full year of 2011, FirstEnergy reported a 21 percent increase in its earnings of $2.22 per share on net income of $869 million and revenue of $16.3 billion. That compared with $2.44 per share on $718 million of net income and revenue of $13.3 billion. For the fourth quarter, the company’s profit increased 26.9 percent to 23 cents per share on net income of $99 million with revenue of $3.9 billion. That was down from 27 cents per share on net income of $78 million and revenue of $3.2 billion.

Betty Lin-Fisher can be reached at 330-996-3724 or blinfisher@thebeaconjournal.com. Follow her on Twitter at www.twitter.com/blinfisher and see all her stories at www.ohio.com/betty.