Damaged Fuel Rods at VA Nuke

Wednesday, October 1, 2014 @ 11:10 AM gHale

There are two damaged nuclear fuel rods at Dominion Virginia Power’s North Anna 2 power plant.

Workers found the problem during the Louisa County, VA, reactor’s scheduled refueling in September.

The Richmond-based utility said about 15 uranium fuel pellets came out of two rods and entered the reactor cooling system.

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Because the radioactive uranium remains contained in the reactor system, the damage has “no radiological consequence to it,” said David A. Heacock, president and chief nuclear officer of Dominion Nuclear, a subsidiary of Dominion Resources Inc., the parent company of Dominion Virginia Power.

“It’s a fairly low safety significance issue,” said Roger Hannah, a spokesman for the Nuclear Regulatory Commission (NRC) in Atlanta. “Even though the fuel is damaged, it’s in a closed system, so you don’t have the concern for an environmental release” of radioactivity.

Cooling water flows though the reactor’s internal cooling baffles at the rate of 300,000 gallons a minute.

In the past 18 months, a jet of water through a millimeter-size hole in the fuel rods’ support structure was squirting over the rods. That flow started them spinning and vibrating, Heacock said, a problem called “baffle jetting” which has occurred at other nuclear reactors. The rods rubbed against the support structure, cutting grooves in them and eventually causing their tops to crack off.

Seven or eight fuel pellets came out of each of the two zirconium-alloy fuel rods, Heacock said. “We have accounted for about eight of the pellets,” he said. “We believe the rest have been pulverized in the normal filtration mechanism,” which will recover the nuclear material.

“We’ve cleaned the entire reactor vessel,” Heacock said. “Now we’re inspecting the entire reactor refueling cavity.”

In the critical area of the replaced assembly, Dominion Virginia Power has installed seven stainless steel rods so coolant flow cannot damage uranium-filled rods, Heacock said.

“The long-term fix is to modify the way the water flows in the baffle so there’s no possibility of baffle jetting,” he said. That modification will occur either in 18 months at the unit’s next refueling or during the refueling after that.

Made from uranium dioxide, the ceramic pellets are about half an inch long and three-eighths of an inch in diameter. A 12-foot-long fuel rod — called a “pin” — at North Anna 2 contains either 360 or 372 pellets, depending upon the vendor. The reactor has 157 fuel assemblies, each of which hold 264 rods.

The damaged fuel assembly is now in the plant’s spent fuel pool. “No abnormal increase was noted on any radiation monitor either after or during fuel assembly movement,” the company told the NRC.

The company used the failed fuel assembly during three 18-month operating cycles at North Anna and was not on any schedule for reuse.

Radiation dose rates around the reactor are 4 percent lower than they were 18 months ago, the company said, because of efforts to reduce the rates.

Refueling outages for Dominion Virginia Power’s nuclear power plants usually take about a month. The latest refueling began Sept. 7.

“At this point,” Hannah said. “we see no reason why, with new fuel in there, they couldn’t restart the reactor.”

Dominion Virginia Power’s four nuclear units produce more than 40 percent of the electricity used by the company’s nearly 2.4 million customers.

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