This article originally appeared in iWWD Feb. Spring 2020 issue as "Dousing Flames"
Of the various forms of power generation that keep a city humming, none demands the same level of attention and care as nuclear power plants. Fire presents a chief hazard at these facilities, posing a special risk because it has the potential to cause serious damage that could jeopardize the ability of plant operators to safely shut down the plant, causing the reactor core to overheat and radiation to leak.
As such, regular testing and preventative maintenance are needed to ensure fire protection systems will perform as expected in the event of a fire. Fire pump failure could spell disaster for a site, but basic testing and maintenance, as well as emergency backup systems, help minimize those risks.
Complying with fire protection regulations
A nuclear power plant in the southeastern U.S. needed to maintain two working primary fire pumps and two jockey pumps or it would be required to take the nuclear reactor offline to comply with enhanced fire protection guidelines issued by the Nuclear Regulatory Commission (NRC) in 2004.
All nuclear power plant systems are required to undergo periodic maintenance and safety checks to ensure systems are working properly. Even during routine maintenance, the NRC requires four pumps to be operational. If repairs are needed and they cannot be completed within the mandated maintenance window—typically three to five days—regulations dictate that the nuclear reactor must be taken offline, which is a consequence that would result in a huge expense for plant operators, as well as repercussions for those who depend on an uninterrupted supply of power.
To meet NRC requirements, the nuclear plant engaged Xylem to provide a temporary fire protection system which could be activated when one or more of the permanent pumps were taken offline for maintenance. The customer needed to ensure the temporary fire protection system was designed to meet the unique flow, head, system and operational requirements of the plant. Additionally, the system had to be installed quickly and needed to comply with plant-specific procedures. Finally, the facility needed a guarantee that temporary fire protection equipment would be available on short notice.
Custom Pump Solution
Designing fire protection systems for nuclear plants is not a one-size-fits all endeavor. Systems must be customized based on individual plant risks, layout and schematics, piping infrastructure and overall plant conditions. In addition to addressing unique plant configurations, custom solutions need to maintain compliance with licensing requirements, as well as integrate rigid NRC guidelines into the distinct environment of an individual plant. This can prove laborious and demands a great deal of expertise.
During the design stage, it quickly became apparent to Xylem engineers that the original nuclear plant layout was not designed to properly address routine maintenance of the fire protection system.
To remedy the situation, Xylem Rental Solutions engaged its dewatering application experts to design a custom manifold, which could hook up to a flange connection on the main fire header, enabling a temporary jockey or main fire pump—or both—to be connected to the system. Based on site conditions and system needs, the Godwin Dri-Prime HL250 and Dri-Prime HL100 pumps were selected to serve as the basis of the nuclear plant’s emergency backup system. The high-pressure, diesel-powered pumping units sit on skids for plug-and-play installation and quick removal in an emergency water pumping situation.
Xylem also worked with the customer to develop a step-by-step procedure for the installation and testing of these temporary pumps to place them in and out of service during regular testing and maintenance of the plant’s fire protection system equipment as required by the NRC.
Once the equipment was fabricated and delivered, installation took approximately a week, followed by a successful one-day test period. Based on the outcome of the initial project, the customer awarded Xylem a multiyear contract to provide fire protection pumps and ancillary equipment on an as-needed, will-call basis. The customer has renewed that contract annually for more than 12 years.
As part of its contracted services, Xylem continues to work closely with the plant management to update the facility’s temporary fire protection pumps as increasing security measures dictate changes to overall fire protection system design.
Aging Plants Require Special Attention
Age is another factor to consider in fire protection systems for nuclear plants.
“New construction of nuclear power plants has ceased and most plants are reaching the end of their initial 40-year operating license,” said Xylem’s pump supplier representative.
The average age of the 97 operating U.S. nuclear power reactors is 38.5 years, according to the Energy Information Administration, and nearly all have received NRC-approved extensions of their operating licenses from 40 to 60 years.
As nuclear plants age, they require more intensive monitoring and preventive maintenance to operate safely. Additionally, equipment obsolescence and system aging issues result in the need to modify, upgrade or replace portions of or complete systems. The NRC requires plants seeking license renewals to develop aging management programs and incorporated aging issues into many of its inspections.
To continue operating, many nuclear plants are taking a proactive stance in preventing aging-related failures and investing in updating their systems.
Over the years, Xylem also has incorporated new technology into the plant’s temporary fire protection system, including a PrimeGuard controller to start and stop the pump automatically without requiring operator intervention and pressure transducers to monitor water levels and pressures in the fire system.
In addition to temporary fire protection equipment and support services, the customer has also expanded the contract terms to provide rental and permanent equipment to other areas of the plant.