MINNEAPOLIS — Xcel Energy is defending cost overruns during the five-year upgrade of its nuclear power plant in Monticello.

The Minneapolis-based utility completed the $665 million project in July, and acknowledged that replacing pumps, filters and other equipment cost more than double the original estimate.

Now, in a state filing, Xcel Energy said the costs were prudent. The company must prove that to Minnesota utility regulators in order to fully recoup the investment by raising electric rates.

Dave Sparby, CEO for Xcel’s Minnesota regional operation, said nuclear power is “safe, reliable, carbon-free and cost-effective.”

At its peak, the construction project at the Monticello plant employed 3,000 workers. The upgrade replaced old equipment to keep the plant running another 20 years, and boosting its power output by 12 percent.