OAK HARBOR, Ohio — Groups that oppose Davis-Besse’s continued operation want a formal hearing to present evidence about hairline cracks that have developed, and continue to grow, in the nuclear reactor’s shield building since the utility applied weather sealant in 2012.

In a filing Monday night with the Nuclear Regulatory Commission’s licensing board, critics claim to have documents that show FirstEnergy wasn’t as transparent and forthcoming about the issue as it should have been when the utility divulged information about the new cracks in the fall of 2013.

FirstEnergy denies those allegations.

The NRC said it will send inspectors to Davis-Besse to examine how FirstEnergy and its contractors arrived at its conclusions while the commission’s licensing board decides about a hearing. The latter could be the last obstacle for FirstEnergy to gain a 20-year extension to Davis-Besse’s operating license, which expires in 2017.

Sealant wasn’t applied to Davis-Besse’s shield building until 2012. Cracks in the concrete found in 2011 have been blamed on harsh weather conditions from the blizzard of 1978. A year ago, evidence showed that the sealant-trapped water caused new cracks, and they have grown from freeze-thaw cycles since 2012.

The NRC said the shield building remains strong enough to repel external forces, such as high winds and tornado-tossed heavy objects. The new cracks are minor but will need to be monitored for the rest of the plant’s operation.

First Published September 11, 2014, 4:00 a.m.