Guide tubes at Lake Wylie plant grew more than expected
Duke Energy has removed test bundles of mixed-oxide or MOX fuel from its Catawba Nuclear Station on Lake Wylie as it investigates unusual physical changes in the assemblies.
Anti-MOX groups say the halt means the testing should start all over again, delaying by years a billion-dollar federal program to use surplus weapons plutonium at Catawba.
MOX fuel mixes conventional uranium with plutonium taken from the nation's surplus stocks to fuel nuclear reactors that produce electricity. Duke is part of a program to dispose of 34 metric tons of plutonium, keeping it out of terrorists' hands.
Testing of the fuel was expected to take more than four years, covering three refueling cycles at Catawba's Unit 1. Instead, the MOX was removed in May, after two cycles and less than three years of testing.
The problem was that alloy "guide tubes" in the MOX assemblies, in which control rods are inserted to shut down the reactor, grew in length. It's not unusual for metals to expand in the intense heat of a nuclear reactor. But these grew more than expected.
Duke decided to remove the four MOX assemblies -- among 189 conventional assemblies -- while it investigated. The utility and the Nuclear Regulatory Commission say the issue didn't jeopardize the safety of the plant, and the reactor was restarted with conventional fuel alone.
But the Union of Concerned Scientists and Friends of the Earth, which oppose the MOX program, called it a potentially serious defect that could deform the fuel assembly and interfere with the ability to shut down the reactor. They say the fuel assemblies should be redesigned and retested, a process they say could take another eight years.
"We think that means Duke will have to repeat the whole test," said Edwin Lyman, a physicist at the Union of Concerned Scientists. The groups say surplus plutonium should be encased in glass blocks, useless to terrorists, instead of burned in commercial reactors.
But the agency in charge of the MOX program, the National Nuclear Security Administration, says it doesn't expect the testing halt to derail its schedule.
"We don't see this as a delaying factor, as it's been portrayed," said spokeswoman Casey Ruberg. "Testing data for the past several years will not be negated and will be valuable as we move forward with this important national security program."
Duke is analyzing the assemblies and might send some to a federal lab in Oak Ridge, Tenn., spokeswoman Rita Sipe said. No decision has been made whether to continue testing at Catawba, she said.
Ruberg said NNSA expects testing to continue later.
The MOX fuel itself performed as expected in the first two testing cycles, she said.
Similar guide-tube growth has been seen in conventional fuel assemblies at other plants, including Duke's Oconee plant in South Carolina. Those parts were built by the French company AREVA, which made the MOX test assembles at the Catawba plant. Modifications allowed the continued use of those assemblies, said NRC spokesman Scott Burnell.
Construction of a $4.8 billion MOX fuel plant at the Savannah River Site near Aiken, started a year ago. It's expected to start operating in 2016.