Dr. Mor & Associates

Media Links

• tampabay.com
• NRC web site
• NY Times report Nov 23 2009
• Repair progress
• Still optimistic Feb 3 2010
• Repairs take longer May 6 2010
• NRC explanation
• Power Engineering
• Power Engineering
• Second delamination
• Tampa Bay Online

Crystal River Nuclear Plant - Concrete Delamination Investigation

In September 2009, a gap (delamination) was detected in the 42" thick concrete containment structure at the Crystal River Nuclear plant.

The containment building wall is engineered to hold in a sudden buildup of heat, pressure or steam inside the reactor building. Just inside the wall is a steel-plate liner three-eighths of an inch thick. The concrete is reinforced with a post-tensioned cables located near the outside face.

The gap was discovered as workers cut a 25- by 27-foot hole in the containment wall so two huge steam generators could be removed and replaced. The utility cut the hole because the reactor building's regular equipment hatch is too small for the generators, which weigh 550 tons each. The plant was not operating at the time, and there was no release of radiation.  
Cutting the hole required cutting a large number of PT cables and removing the concrete with high pressure water cutters.
Due to the sensitivity of the structure, a thorough investigation into the causes was required before any repairs were allowed.
The owner assembled a team of experts in the construction and nuclear industries to determine the "Root Cause" of the failure and and create a comprehensive report for the Nuclear Regulatory Comission (NRC).  Dr Avi Mor was the lead concrete expert on the Root Cause team.
The investigation determined that the delamination occured as a result of detensioning the PT cables in preparation for the concrete removal.  The resulting stresses exceeded the capacity of the concrete that had limited tensile strength due to its composition (mainly the aggregates used).
(see explanation by NRC)
Before any repairs could be attempted, a complete Non-Destructive investigation of the structure determined the location and scope of the delamination.  Complex finite element analysis was performed by others to determine how future detensioning and retensioning of cables must be done in order to prevent a repeat of the delamination during the repair process.
The delaminated area concrete was removed and new concrete was placed in the gap.
However, the retensioning process appears to have caused new delaminations in part sof the original structure - prompting a new evaluation of the future of the plant.
At this time (July 2011) the owner is still attempting to come up with a new repair methodology that will allow the plant to continue operations for more than twenty years.

Crystal River Nuclear Power Plant

Overview of Unit 3 at Crystal River Nuclear Plant

Opening in Containment Structure at Crystal River Nuclear Plant