Entergy Responds to NRC Claim that Palisades Nuclear Plant at Risk of Pressurized Thermal Shock
Responding to a recent claim by the Nuclear Regulatory Commission (NRC) that the Entergy’s Palisades nuclear power plant is at risk of pressurized thermal shock., the Louisiana-based company said the plant "is a safe and secure facility [and has a] license to operate … through 2031."
The NRC held a webinar this week to discuss pressurized thermal shock and how it relates to the nuclear plant in Covert, Mich. The federal body said the phenomenon could occur in a "rare accident scenario" in which a large amount of cold water is injected into the reactor resulting in its rapid cooling. This rapid cooling increases the stresses on the vessel and could challenge the vessel’s integrity, especially as it ages and becomes more brittle.
The NRC has said that the Palisades reactor vessel will reach its “embrittlement limits” in 2017, and if operators don’t take steps to address limit exceedance next year, it will be forced to shut down in 2017. Entergy said it will conduct all necessary tests and inspections during a refueling outage this fall, and that it will submit an updated evaluation to the NRC in spring 2014.
In its webinar, the NRC acknowledged that "only the most severe forces produces any risk," and that rapid cool-down to 200F below operating temperature was needed to produce any risk. "Operational controls limit the likelihood of such cooldowns occurring." Palisades operates in compliance with NRC embrittlement limits, but its vessel is "one of the most embrittled plants" in the nation, the NRC said.
Entergy had several options for operation beyond 2017, it noted, however. As well as annealing—using a heat treatment to increase ductility of the vessel and reverse embrittlement—it could provide an analysis to provide a plant specific safety justification, or use a regulatory option (10 CFR 50.61a) that would let Entergy continue operations after 2017. Under this "viable option," the NRC would need to analyze data, check embrittlement, and check for flaws, it said.
“This is not a new topic or one that is unique to Palisades," Entergy said in a statement on Monday. "In fact, for decades pressurized thermal shock has been well understood and well monitored by the owners and operators of the nation’s pressurized water reactors."
Entergy said every pressurized water reactor plant in the U.S. is required by the NRC to continually update calculations to confirm reactor vessel strength—meaning "every plant must conduct periodic reactor vessel inspections and analyze reactor vessel samples. Consistent with these NRC requirements, Palisades will conduct these inspections and analysis during our refueling outage this fall," it said.
"We have every reason to believe the test results will again demonstrate the safety and strength of the Palisades reactor vessel— which will enable us to continue operating through the end of our license in 2031." Entergy said.
The 793-MW Palisades, which entered service in 1971, is located on the shore of Lake Michigan. In 2007, the NRC renewed the reactor’s original 40-year operating license for an additional 20 years until 2031.
Sources: POWERnews, NRC, Entergy