Nuclear Power Plant Intake Cavity Repairs

An east coast nuclear plant has taken a proactive approach to dealing with deteriorating concrete caused by chloride induced embedded steel corrosion. The plant’s two pressurized water reactor units take in ocean water to cool its steam-driven turbine condensers plus other water-cooled primary and secondary system heat exchangers. Over time, the intake cavities began to spall. Recognizing that high chloride ocean water and humidity causes the existing steel reinforcement in the concrete intake cavities to corrode, the plant developed a multi-year repair and protection solution to extend the life of these important infrastructure elements.

 

Preparation Training and Repair Strategy

STRUCTURAL, as part of a larger on-going repair contract, recently repaired three intake cavities during a scheduled outage in winter 2014. Repairing the spalls and preventing further corrosion was critical. Any concrete that could have fallen into the cavity might have damaged the system and caused a costly shutdown for this high production facility. The owner elected to install an impressed current cathodic protection (ICCP) system to provide long-term protection to the intake cavities.

Serving as the general contractor on the repairs, STRUCTURAL worked within the plant’s Nuclear Quality Assurance (NQA) program during the scheduled shutdown to repair the deteriorated concrete and install the complex cathodic protection system.

Leading up to the outage, prospective crew members assembled at STRUCTURAL’s training facility. Over the course of a week, 70 employees were screened, trained, and tested on all plant entry requirements by plant personnel. Plant-specific and project specific computer based tests (CBT’s) were also administered.

In addition to standard plant training, crew members were also given project-specific instruction including practical hands-on training. That training included the use of a full size mock-up of a cavity where dry runs were completed for critical tasks and safety-related items that stepped through the work procedures developed during the pre-project planning process.

Once the plant had dewatered the cavities, STRUCTURAL performed a wash down and installed an innovative cutting guide system. Designed by STRUCTURAL, this unique shelving system consisted of templates and slotted steel angles. It was designed to enhance safety and mitigate the fatigue of the workers while incorporating guides for the installation of the ICCP system’s anode grooves.

Crews saw cut and chipped out 1-inch slots where the ICCP titanium ribbon was installed. A pressure wash was performed to clean off the brine water and slurry from the walls. The system’s anode ribbons, grounds, and reference cells were installed. Crews welded the ribbon with a spot weld machine, carefully ensuring the titanium ribbon didn’t come into contact with any steel embedded within the concrete. Such contact could short the system. Constant monitoring was necessary to ensure that system shorts were not occurring throughout the installation.

To protect the surrounding ocean from debris and water used in saw cutting operations, STRUCTURAL put a water collection system in place that collected and treated water. The treated water then traveled into the facility’s sanitary plant.

Critical to successfully implementing an ICCP system, the repair material selected needed to have the ability to not be a deterrent to the designed current output to protect the steel. All anode slots were filled with a cementitious grout and a 3-inch wide cementitious coating.

 

Continued Contract Success

Without a single safety incident, STRUCTURAL completed the three intake cavity repairs on time and within the parameters of the scheduled shutdown. Seven intake cavities in total have been completed and the team continues to provide these services at the plant with two years and five intake repairs left. As a result of the successes throughout this contract and consistently exceeding client expectations, STRUCTURAL has also been awarded additional specialty repair projects at the facility.