Rainwater began unexpectedly infiltrating an east coast nuclear power plant’s switchgear roof resulting in a costly, unplanned shutdown. The plant conducted a large-scale evaluation to determine the best prevention plan to eliminate similar events in the future. The evaluation suggested that the plant should not defer a long-term project using a comprehensive approach to systematically replace the roof systems. The owner decided to proactively address all of the roofing within the plant facility to provide a long-term solution to prevent any future unplanned shutdown events
Collaborative Repair Strategy
STRUCTURAL was selected to repair nine roofs at the plant because of previous history of successful work at the plant and the expert knowledge of nuclear facilities the team encompasses. Working with STRUCTURAL TECHNOLOGIES’ moisture control solution builders, the team combined nuclear facility expertise with a strong roofing repair portfolio.
STRUCTURAL worked with STRUCTURAL TECHNOLOGIES to inspect field conditions and determined the design challenges before the project began. The team continued to bring solutions to meet new challenges once the construction started, which kept the project schedule on track and avoided extra incurred costs.
The repair strategy evaluated the types of roofs and the components beneath them. For the roofs that were categorized as critical, the best solution was determined to be a built-up roofing system (BUR) with three plies of modified bitumen (mod-bit) above a layer of mod-bit vapor barrier and a fiberglass-covered gypsum board.
Non-critical roofs were categorized based on the amount of foot traffic. Those with more foot traffic were determined to need a BUR system with two plies of mod-bit with a layer of mod-bit vapor barrier and a fiberglass-covered gypsum board beneath. For the roofs with little foot traffic, the repair strategy included a single-ply PVC roof membrane on top of a roof board.
Planning, Designing, and Executing
STRUCTURAL worked closely with the client to provide a full mock-up in-house to demonstrate the repair process and how to address more than 30 details found on the various roofs. After the details of the project were fully planned out, STRUCTURAL began to install the BUR system. Crews first removed the existing roofing, which measured up to 15 inches thick in some areas. Special precautions were made to ensure that the workers could safely perform work without cutting or drilling into embedded live conduits that may have been installed in the high flutes of the sheet metal deck pans.
A roof that was not structurally sloped required a thicker buildup of materials to provide positive slope to the drains to prevent ponding. STRUCTURAL installed a lightweight insulating concrete with four-way positive drainage. The lightweight concrete provided a safer, quicker, and cost-efficient option. STRUCTURAL had to be extremely cautious in protecting the areas of repair each night and ensure the work was completely waterproofed, also known as night seals. Whatever was removed during the day’s work had to be roofed in with a temporary roof or finished system at the end of the day. Whether installing the vapor barrier or the built up sections, this process remained the same no matter the roof type.
Throughout the roofing repair, crews faced the challenge of operating in the extremely high ambient heat generated by the environment and also by operating equipment. During the particularly hot summer months, crews experienced temperatures up to 105 degrees. In addition to early-morning start times to avoid doing the labor intensive tear-off in in the heat of the day, STRUCTURAL carefully monitored heat stress stay times to address these high temperatures. Other safety and efficiency procedures included highly detailed pre-job meetings held each morning. Event -free checks and job hazard analysis were performed at the work site to identify and discuss any changed conditions that would affect work and formulate safety solutions proactively.
Schedule was critical, as the work had to be complete by Christmas to avoid poor weather conditions and to keep within the oversight budget of the fiscal year. In the first year, STRUCTURAL exceeded expectations for completing the work ahead of schedule under budget with zero safety incidents.
Proactive Approach Equals High Quality Results
The first three roofs have been completed and STRUCTURAL has had zero items on the punchlist. The proactive efforts of the client to address the roofing at this facility continue to be vital in avoiding costly emergency shutdowns (SCRAMS) and unplanned outages. The repaired, watertight roofs will help to prevent these events and continue the safe and reliable operations of the plant. STRUCTURAL’s roofing work at the plant continues to be completed with safely delivered services and high quality results.