Xcel Energy temporarily stopped load following operations at Prairie Island in Minnesota after NRC determined in a June 30 inspection that plant procedures should have required further analysis of such operations due to their long-term effects on safety.
NRC said in a letter released July 30 that agency inspectors identified a very low safety significance finding when Xcel "failed to incorporate a restriction to prohibit load following into plant procedures." The operating procedure ensures that control rods used to shut a reactor are no longer deployed for load following after a certain number of years.
Xcel continued to conduct flexible power operations at the 590-MW Unit 1 "more than 30 times" since Sept. 3, which could have affected the unit's control rods, NRC said.
That could have led to the rods being unable to perform safety functions and/or complicated a plant shutdown, the agency added.
Xcel has been conducting such operations, lowering output for short periods, at its Prairie Island and Monticello nuclear plants since December 2018, the company has said.
Flexible power operations allow the company's reactors to occasionally lower output "to support grid stability and match the variable amount of wind and solar energy on Xcel Energy's system," Xcel has said.
David Lochbaum, a nuclear engineer and former director of the nuclear safety project at the Union of Concerned Scientists, said in a July 31 email, "This is a very impressive catch by the NRC," since such safety issues and regulation violations can be easily missed.
Xcel spokesman Randy Fordice said July 31 the findings "have already been resolved in working with the NRC. While there was no impact to safety, we have updated our documentation, and have analyzed equipment related to the flexible operations for both units."
Xcel "implemented actions to ensure that Unit 2 would not perform flexible power operations until completion of a prompt operability determination and established controls to ensure Unit 1 would not undergo flexible power operations until after the next refueling outage," NRC said.
Prairie Island-1 is scheduled to refuel this fall, according to S&P Global Platts data.
The licensee "completed a prompt operability determination and concluded that [Unit 1's control rods] were operable," NRC said.
"There were no anomalies noted during the last flexible power operation on Unit 1 on May 2," it added.
Xcel determined the 585-MW Prairie Island-2 could resume flexible power operations July 12, NRC Region III spokeswoman Victoria Mitlyng said July 31.
Xcel conducted an evaluation of whether there should be limits on load following at the 691-MW Monticello "and no significant concerns were identified," Mitlyng added.
