For decades, the U.S. fleet of nuclear power facilities has efficiently and reliably generated low-carbon electricity. Inside each facility, reactor coolant pumps (RCPs) and other components play a critical role in creating this electricity. This equipment, however, operates for extended periods of time under harsh conditions. Eventually, these components need to be refurbished or replaced.
The nuclear industry is constantly exploring innovative and efficient ways to complete these replacements and to ensure operational excellence. In 2015, Dominion Virginia Power completed one of the largest RCP refurbishment projects in the U.S. at the Surry Power Station in southeastern Virginia.
The project scope included five pump replacements.
The facility partnered with an international nuclear energy services company to renovate and qualify four 12-foot, 24-ton pumps, including two from Dominion’s closed Kewaunee Power Station in Wisconsin. One additional pump previously refurbished by the nuclear energy services company was used to complete the project scope.
Deciding to Replace RCPs
In 2014, intergranular stress corrosion cracking (IGSCC) was found on turning vane bolts in a U.S. power plant. These bolts secure the turning vane diffuser assembly inside the RCP, located above the pump impeller.
The original equipment manufacturer identified a problem with pumps manufactured with 1-inch-diameter turning vane bolts.
After evaluating this issue, Dominion decided to upgrade and replace all its facilities’ RCPs that contained 1-inch-diameter turning vane bolts. At Surry, five RCPs were affected: two in Unit 1 and three in Unit 2. Dominion contracted the nuclear energy services company to refurbish the RCPs, including replacing the turning vane bolts. This work was performed in Unit 1 during the spring 2015 outage and Unit 2 during the fall 2015 outage.
Overcoming Obstacles to RCP Refurbishment
With an aggressive outage schedule, spare pumps had to be obtained in 10 months—a monumental task when, historically, lead times to secure RCPs were two to three years.
Faced with such a challenge, the nuclear energy services company looked into reclaiming two RCPs from Dominion’s retired Kewaunee plant in Wisconsin and refurbishing them to like-new conditions. This innovative idea presented significant challenges that needed to be addressed before the company could proceed with purchasing the pumps from Kewaunee:
- Ownership: The ownership of the pumps had to be resolved. Kewaunee is part of the unregulated business at Dominion, but Surry is a regulated business facility. Moving assets from unregulated to regulated facilities required meeting certain regulations.
- Condition: The team had to determine whether the pumps were in a condition to support more than 20 years of service at Surry after operating for more than 30 years at Kewaunee. To be refurbished for another facility, the pumps could not be degraded.
- Codes and licensing: American Society of Mechanical Engineers (ASME) requirements vary from plant to plant based on state and date of construction. As a result, the team had to evaluate each state’s codes and standards to determine if the Kewaunee pumps were built to code requirements that satisfy those governing Surry.
- Physical interchangeability: A number of physical requirements had to be evaluated, including the size of the Kewaunee pump and the Surry pump casing, the Kewaunee pump flow rate and pressure compared with the Surry pump, the location of the interface for the motor (coupling, motor stand bolts), and the location of the piping connections (seal water, cooling water).
The nuclear energy services company performed a detailed engineering study that confirmed that the Kewaunee pumps were a safe and reliable solution for installation at the Surry station. The team then decided to proceed with the purchase.
Undertaking the Refurbishment Project
The RCP refurbishment project included replacement of the shafts, impellers, couplings, bearings and all bolting on the pumps. The accelerated delivery schedule required the nuclear energy services company to manufacture these replacement parts in less than six months—a task that normally takes one to two years.