The Calvert Cliffs Nuclear Power Plant (CCNPP) is located on the western shores of the Chesapeake Bay in Lusby, Maryland. Named for the nearby bluffs, Calvert Cliffs generates a significant amount of electricity used in Maryland. The facility has two nuclear reactors. When deterioration of steel on the intake floor, circular water pump bowels (CWB) and salt water pits (SWP) became severe, CCNPP contacted Structural Preservation Systems (SPS) for assistance. The owner wanted to repair the concrete surfaces with a system that would help prevent corrosion and last for a period of approximately 20 years to reduce plant maintenance costs.

For the $3.25 million project, the scope of work encompassed three main work areas: the intake floor, circular water pump bowels (CWB) and salt water pits (SWP). In order to achieve the owner's goal, the SPS team utilized an impressed current cathodic protection (ICCP) system to help prevent corrosion of the new and existing reinforcing steel in the floor. CorrPro Companies Inc. of Medina, Ohio provided all the ICCP system materials and technical assistance on the systems capabilities. With impressed current cathodic protection systems, a small, direct current is passed from a permanent anode to the reinforcing steel. An external power supply is connected between the anode and the steel with the appropriate polarity and voltage to prevent the reinforcing steel from giving up electrons. This system repels chloride ions away from the reinforcing steel toward the installed anode and provides flexibility in adjustment since the current or output can be easily adjusted.

For the 8,800 square foot intake floor, an average of 6.5 inches of concrete was removed, a cathodic protection ribbon was installed to prevent continued steel deterioration, and a new concrete floor was poured to replace the old floor. With the circular water pump bowels (1,050 square feet) and salt water pits (600 square feet), concrete was removed to 1-inch under the reinforcing steel, a cathodic protection ribbon was installed, and the concrete was replaced. In areas where concrete was removed, the ribbon was installed at 12 inches on center and 1-inch above the reinforcing steel. Then the patches could be formed and repaired with new concrete. In areas where the concrete was sound, the ribbon still had to be embedded into the concrete.  To allow for proper ribbon placement, 1-inch by 2-inch slots were cut into the concrete. These slots then had grout placed over them.  Approximately 3.5 miles of saw-cutting was required to install the ribbon in the concrete surfaces.  

Placing the overlay on the intake structure floor presented other challenges. Since the ICCP system is 1-inch above the reinforcing steel and cannot touch the steel (this would result in a short of the system, which renders it useless), it was challenging to determine how to place the concrete and protect the ICCP ribbon. To overcome this challenge, the entire floor was decked with 2 x 10s. As placement and finishing operations progressed, boards were pulled up and removed from the work area. Additionally, the location of the ready-mix truck access in relation to the placement point exceeded 400 feet. This required a concrete mix design that utilized ice, retarder and plasticizer to ensure all placed concrete met strict Nuclear Regulatory Commission (NRC) criteria. This also provided the workers good workablility and placement durations. Preplanning meetings two days in advance of the placement were facilitated to ensure personnel assignments, supplier requirements, and security criteria were all considered and accounted for during the project.

One of the major challenges for this project was that all work had to be performed while the plant was fully operational as it was imperative that the plant maintain 100 percent power output. Foreign particles (i.e. dust/debris) needed to be contained so they would not get into the motors, bearings, windings and other mechanisms. In addition, the crew needed to be extremely careful while they were working in the vicinity of operating plant equipment. To achieve the required amount of protection, a number of systems were used.  A protection net was installed to a height of 8 feet to prevent water and debris from entering any equipment and panels. In addition, plastic walls were draped around the entire perimeter of each phase and were required to be water-tight to prevent water and slurry from acting as foreign materials to panels, drains and sumps. At all motor casing openings, frames were built to install filtering media to trap any possible dust so it did not get into the motor windings.  Hydro-demolition was used to remove the majority of the concrete and all hand chipping was performed under heavily wetted conditions to minimize any dust. All debris was vacuumed out of the structure with state-of-the-art equipment. The water was pumped from the debris and neutralized to a pH level below 9.0 before being pumped back through the plant water treatment facility for final adjusting.

The work schedule was also a major challenge on this project. The schedule was based on hours - not days - and all work was performed around trip-sensitive equipment (equipment that is designed to "trip" or shut down the reactors in the event of an emergency).  SPS had to ensure that there was forward-thinking with each schedule activity since all other groups and plant resources worked within the same schedule. Any delay to SPS activities could cause an impact to these groups' planned projects and maintenance activities. These group projects are imperative to the safe and continued operation of the plant and are dictated by the NRC.

Crews found themselves working in very small spaces around some of the plant equipment. To accommodate the tight space constraints, the hydro-demolition contractor, Rampart Hydro Services of Coraopolis, Pa., designed and built a custom concrete removal machine to expedite the work. The machine was a three-wheeled hydraulically-powered unit that could fit into areas as narrow as 28 inches. The unit was controlled by an umbilical connected to the main control panel so the operators could maintain a safe distance from the machine and plant equipment. The hydraulic pumps were operated on a 208v, 3-phase power pack.  The hydraulic oil was food-grade and biodegradable. This was an important feature because of the close proximity to the Chesapeake Bay.

As with any project, safety was extremely important and increased controls were incorporated into the crews' daily activities. The SPS team used a combination of nuclear power plant briefs, SPS internal Job Safety Analysis (JSA) forms, as well as the concepts of "Questioning Attitude" and "STAR" (stop, think, act, review). Crews were consistently briefed with any job condition update. These job briefs frequently occurred at any time during the work day to include when new conditions were noticed or changes in the planned procedures needed to be adjusted to keep all personnel and equipment safe. SPS also found that the focus on job safety had great dividends in the quality control area of the project through the above concepts of Questioning Attitude and STAR. By using these HU (human performance) tools, clear expectations of the tasks at-hand were defined and when results differed from expectations, SPS was able to make the correct adjustments to maintain the highest level quality. Another key aspect is the concept of facilitating a "lessons learned" meeting. These meetings reviewed all of the prior work activities and further adjustments were made to make each successive phase safer and more efficient that the previous.

The first phase of the project began in October 2006 and was completed in early 2007. Phase one represented approximately 15 percent of the project scope. The remaining 85 percent of the work (five phases) was completed between April and December 1, 2007, which shows a remarkable change in efficiency of the project, when compared to the duration of the first phase.