The Crystal River reactor went offline in September 2009 for refueling, OTSG replacement (once through steam generator), and 20% power up-rate outage. In preparing the containment building for making the opening to replace the two OTSG's, tendons in the containment building wall were detensioned. During the concrete removal in creating the opening workers discovered a large gap in the concrete of the containment building wall. The main cause of the gap, which further engineering analysis determined was a large delamination, was attributed to the scope and sequence of the tendon detensioning. The plant had originally been scheduled to restart in April 2011, but the project encountered a number of delays. Repairs were successful, but additional delamination began to occur in adjacent bays. After several months of analyzing options, Duke Energy senior executives announced in February 2013 that the Crystal River Nuclear Plant would be permanently shut down. The coal-fired units are not affected.