COVERT TOWNSHIP, MI — A piece of metal from a broken
impeller blade has lodged in the reactor vessel at Palisades Nuclear Power Plant. Workers discovered the issue during the nuclear power plant's scheduled refueling and maintenance shutdown, which began Jan. 19.
The metal is 5 inches by 12 inches long, said Lindsay Rose, spokeswoman for Entergy Corp., which owns Palisades. The piece is wedged into the reactor vessel between the vessel wall and the flow skirt, inside the vessel.
"It's physically separated from the fuel," Rose said in an interview with the Kalamazoo Gazette. "It's not a loose piece floating around. It's firmly wedged into place."
Efforts to remove the metal have proved unsuccessful. At this point, Entergy plans to leave it in place, saying it does not pose a safety risk.
"We took steps to remove it. We've thoroughly analyzed it and we've determined that, based on the location of where it is, it's not going to have any impact on safe operations. We do not believe it is going to move from its location," Rose said. "It has not compromised safe operations and it is not expected to."
Rose said she did not have any information about when the metal piece might have broken off the impeller, which has been replaced. An impeller is a rotor that is used to pump water within the reactor.
The Nuclear Regulatory Commission is aware of the issue and its on-site inspectors are monitoring the situation, NRC spokeswoman Viktoria Mitlyng said.
"We are aware that there is a small piece of metal that is stuck in the reactor. The company has tried different methods for removing it and it is wedged really tightly," said Viktoria Mitlyng, senior public affairs officer for the NRC, in a phone interview. "With some of the more intrusive methods that could be used, there's a danger of actually damaging the vessel. We don't know what the resolution is going to be, but we're following this issue."
Entergy Corp. bought Palisades from Consumers Energy in 2007 for $380 million. The one-reactor plant, which is located along Lake Michigan in Covert Township, supplies about 20 percent of Consumers Energy's power. The facility came online in 1971 and its license runs until 2031.
The plant has shut down at least 10 times since 2011 for repairs, including a month-long shutdown in 2013 to replace the bottom of its safety injection refueling water tank. That shutdown came after approximately 80 gallons of highly diluted radioactive water leaked out and made its way into Lake Michigan in May.
The NRC will have the final say on whether the metal represents a safety-significant issue, Mitlyng said.
"If they propose to leave the metal in the reactor core, they have to provide analysis and justify to the NRC that leaving that in there would not have an impact on the safe operation of the reactor," she said.
Mitlyng said plants have been able to operate with "similar matter" in the reactor.
"However, licensees are required to evaluate the nature of the material and determine whether there will be an adverse impact on safety," she said.
The NRC and its experts will then review the evaluation to determine whether the plant can continue to operate safely.
While he did not have firsthand information about the specific situation at Palisades and could not comment on it, there have been at least three other instances in the U.S. of reactors that operated with metal debris inside, said David Lochbaum, director of the nuclear safety project at the Union of Concerned Scientists.
Lochbaum said he experienced one of those instances first-hand.
When he was stationed at the Browns Ferry nuclear plant in Alabama in January 1980, workers kept track of fuel bundles by moving metal squares on vertical wooden boards.
While one of the three reactors at the plant was shut down for refueling, "the tag board was knocked over twice, dumping dozens of metal tags into the spent fuel pool and onto fuel bundles to be reloaded into the reactor core," he said in an email. "The metal tags were just large enough to block off flow through a bundle. We looked for but did not find all missing tags, and had to analyze the 'what if' scenario if a tag got carried into the reactor vessel. Because it would only have caused overheating damage to one fuel bundle, an outcome within the design of the plant to withstand, we were allowed to restart. The missing tags were never found, but they never caused problems wherever they went."
Quad Cities Generating Station in Illinois also encountered loose metal parts with minimal problems, Lochbaum said.
However, in 1992, the Connecticut Yankee nuclear plant experienced more serious damage when workers removed the thermal shield, a metal plate that was designed to act as insulation but was found to be unnecessary. When cutting through the plate, the workers created metal slivers and flakes that were not fully removed before the reactor started, Lochbaum said.
"It damaged the metal fuel rods either by direct impact or by lodging against some of the framework holding the fuel rods. Water flowing past vibrated the debris against the fuel rods, wearing it away. Workers had to shut down the reactor and inspected each and every fuel rod for signs of damage — replacing the damaged fuel," he said.
Until the NRC is satisfied with Entergy's evaluation of the situation, Mitlyng said, Palisades will not be allowed to restart.
"Our inspectors are evaluating the activities as they unfold," Mitlyng said. "What I can tell you is that we will have to be comfortable with the analysis and their proposed solutions before the reactor can return to power."
Yvonne Zipp is a staff writer at the Kalamazoo Gazette. Email her at yzipp@mlive.com or follow her on Twitter.