Nuclear plant outage continues power uprate work
Late last summer, Mark Schimmel, Monticello Nuclear Generating Plant site president, offered a telling observation about the plant’s current outage.
Shortly after taking over in June, Schimmel guaranteed during an interview the scope of work encountered during the venerable utility plant’s 26th scheduled refueling outage and power capacity expansion project would rival any on-site activity that occurred during the plant’s original start-up during the early 1970s.
And just before the start of a February plant tour, Schimmel added the following: “We’ve got hundreds of additional people here we typically would not have.”
The current outage began early last Saturday. Approximately 2,000 contractors – many of whom come to the Monticello area from other parts of the country, providing a boon to the local economy – are working to complete the last round of major equipment upgrades to increase the plant’s generating capacity.
Refueling outages generally last four to six weeks. Because of the added work during this outage, plant outage activity is expected to run a few weeks longer than usual.
The improvements will increase capacity to 671 megawatts.
The Monticello plant generates enough electricity to power nearly 500,000 homes.
“Typically, we shoot for about a 35-day refueling outage,” said Terry Pickens, Xcel Energy’s director of nuclear regulatory policy. “This refueling outage will be quite a bit longer because of the final modifications for the extended power uprate. We’ll still be replacing about one-third of the reactor’s 484 fuel assemblies.”
Tom Hoen, Xcel Energy media relations representative, said completion of the Monticello power uprate process represents a nine-year effort by the utility.
The plant’s two previously scheduled outages also included installation of major equipment. “In 2011, the plant’s new main transformer and the new steam dryer replaced original plant equipment,” Hoen said. “The old steam dryer was removed in one piece. That was an industry first. It was shipped to Utah for disposal.”
Utilities have been using power uprates since the 1970s to increase power output of nuclear plants. According to the U.S. Nuclear Regulatory Commission (NRC), components such as pipes, valves, pumps, heat exchangers, electrical transformers and generators, must be able to accommodate the conditions that exist at the higher power level. Higher power involves increased steam and water flow through the systems used in converting thermal power into electric power. According to Pickens, when the Monticello Nuclear Generating Plant was originally licensed, nuclear power was in its very early stages in the United States.
“Monticello is probably one of the five oldest plants in the country,” Pickens said. “The NRC was very conservative when it put its safety limits in place. So when they established our thermal power limit, they made sure we had plenty of margin. The NRC was comfortable with us operating at a little higher limit.”
The power uprate is really focused on taking the plant’s turbines, generator, feedwater heaters and other balance of plant equipment and improving them.
Jeff Davis is the Monticello Nuclear Generating Plant’s operations support manager. During a pre-tour briefing, he also explained other equipment changes.
“The feedwater pumps will get significantly bigger,” Davis said. “We need more water to go through the core to generate steam. We’re also going to change our electrical system, namely our offsite power transformers. We’re adding another 13,800-volt electrical distribution system to power those new motors. The Monticello plant is one of the first ones in the industry to change out its power distribution system. One of those transformers is currently out of service,” he said.
How much longer will the Monticello Nuclear Generating Plant keep operating? Well, according to Pickens, Xcel Energy has increased the plant’s lifespan from 40 to 60 years via federal relicensing.
The cost of that process was around $25 to $28 million. “We’ve renewed the license for Monticello with the U.S. Nuclear Regulatory Commission and can operate until 2030,” he said. “That was a comprehensive process. We spent about three years doing evaluations of long-lived, passive plant components.” Picken said Xcel isn’t prohibited from going for another 20-year renewal come 2030. “The NRC is doing research along with the U.S. Department of Energy to make sure it would be safe to operate the plant,” he said. “Once those agencies have done that, then we [Xcel] can go through economic evaluations to consider whether or not we would operate beyond 2030. Monticello is good until then. We have sufficient dry cask storage capacity.”
During refueling outages at the Monticello Nuclear Generating Plant, Xcel Energy purchases power from the Midwest Independent Transmission System Operator (MISO) or directly from other utilities or increases electricity production at its other generating plants to ensure an adequate customer power supply.
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