Damaged Nuclear Fuel Rods Found in North Anna Reactor

Dominion Virginia Power found two damaged nuclear fuel rods in Unit 2 of its North Anna Power Station located in Louisa County northwest of Richmond. The discovery was made during a regularly scheduled refueling outage that began on Sept. 7.

The company believes the fuel rods were damaged as the result of “baffle jetting.” The phenomenon occurs when water jets through a small hole in the fuel rod support structure, causing the rods to vibrate and spin. As the rods rub against the structure, grooves are cut in the zirconium-alloy material, which causes the rods to eventually break open.

Dominion thinks that about 15 uranium pellets came out of two rods and entered the plant’s primary reactor cooling system. The North Anna units are pressurized water reactors, so reactor coolant is contained in a closed system. Thus, the damage resulted in very little radiological consequence and poses no environmental release concerns.

The fuel assemblies had been in service for three 18-month operating cycles and removal was planned during the current refueling outage. Each fuel rod is 12 feet long and contains either 360 or 372 uranium pellets, depending on the manufacturer. The reactor has 157 assemblies with 264 rods in each.

The Nuclear Regulatory Commission was informed of the problem and considers it of fairly low safety significance. Dominion says it accounted for eight of the pellets and believes the rest were pulverized and removed through normal reactor filtration mechanisms.

As a temporary fix, Dominion installed seven stainless steel rods to protect the uranium-filled rods. During a future refueling outage, it intends to modify the way water flows in the baffle area to prevent the possibility of baffle jetting.

Aaron Larson, associate editor (@AaronL_Power, @POWERmagazine)

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