Spent nuclear fuel shifted

Sep 1 - McClatchy-Tribune Regional News - Rusty Dennen The Free Lance-Star, Fredericksburg, Va.

In another indication of the power of last week's magnitude-5.8 earthquake, officials at North Anna Power Station said yesterday that 25 of 27 vertical steel casks that hold highly radioactive spent fuel shifted on their pads.

Richard Zuercher, spokesman for Dominion power's nuclear operations, said none is leaking, all are intact, and there is no danger to the public or plant employees.

"The earthquake did move, slightly, some of the dry storage casks on the pad," he said. The steel casks, which weigh up to 115 tons when loaded, shifted between an inch and 4 inches.

"We're evaluating whether we need to move them back," Zuercher said.

Other newer steel and concrete casks that sit horizontally on pads sustained some minor "cosmetic" damage, Zuercher said. "Everything there is intact and easily fixable." Thirteen of those casks also contain spent fuel.

The fuel for North Anna's two reactors is enriched uranium dioxide, compressed into small ceramic pellets and stacked in metal-alloy tubes called fuel rods.

The rods are bundled together in 8-inch by 14-foot fuel assemblies. There are 157 fuel assemblies in each reactor.

After powering each reactor for about nine months, the fuel is spent, then shifted into a swimming-pool-like container to cool underwater for several years.

When cool enough, the fuel assemblies are shifted to the casks and stored outside the reactor containment domes on pads in a secure area. Each cask contains 32 fuel assemblies.

Plans for a permanent, national repository for the fuel, which remains radioactive for thousands of years, are still in a holding pattern. So the material is accumulating at the nation's 104 commercial nuclear reactors.

Environmental groups argue that spent-fuel pool and storage casks are inviting targets for terrorists; the industry maintains both are safe and secure.

The topic has come up in recent years at North Anna because Dominion has an application pending with the NRC for a third reactor. The plant is on Lake Anna in Louisa County, near Mineral.

The news about the fuel-storage casks comes as a special Nuclear Regulatory Commission team continues its work at North Anna. The team arrived earlier this week to look into reports that ground motion from the quake may have exceeded the plant's design.

That vibration led to a loss of offsite power, triggered an automatic shutdown of the two reactors and damaged some bushings on the main transformers, along with some pipe insulation. Some minor damage to support buildings was also reported.

The plant's engineers and the NRC inspectors "are basically inspecting everything," Zuercher said, including all structures, pipe supports and hangers, and all system components, including pipes, valves and electrical components.

He said about 40 percent of the inspections have been completed on Unit 1, 29 percent on Unit 2. Both reactors remain shut down, and will remain that way until the inspections and analysis are complete.

He said that 44 percent of inspections of buildings at the plant are done.

"To date, there's no significant damage to any safety-related equipment" or systems for shutdown and cooling the reactors.

Zuercher said the NRC team, which includes seismic and technical experts, is expected to be at North Anna through the end of the week. Then they will look at their findings and return for a follow-up visit. At some point, they will hold a public meeting on what they found.

Meanwhile, North Anna is awaiting an analysis of 36 "scratch plates" that recorded the ground motion at Unit 1. A diamond stylus etched a record of the shaking on each metal plate. That data, which will tell whether the plant exceeded its design for what's known technically as "ground acceleration," could be available tomorrow.

Rusty Dennen: 540/374-5431

Email: rdennen@freelancestar.com

Dry cask storage allows spent fuel that has already been cooled in the spent-fuel pool for at least a year to be surrounded by inert gas inside a container called a cask.

The casks are typically steel cylinders that are either welded or bolted closed. The cylinder provides a leak-tight containment of the spent fuel. Each cylinder is surrounded by additional steel, concrete or other material to provide radiation shielding. Some of the cask designs can be used for both storage and transportation.

There are various dry storage cask designs. With some, the steel cylinders containing the fuel are placed vertically in a concrete vault; other designs orient the cylinders horizontally. The concrete vaults provide the radiation shielding. Other cask designs orient the steel cylinder vertically on a concrete pad at a dry cask storage site, using both metal and concrete outer cylinders for radiation shielding.

-Nuclear Regulatory Commission