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Plant to replace reactor cover

The 83-ton lid, due to arrive in September, will shore up the nuclear plant and help avoid a corrosion problem like one at an Ohio plant.

By ALEX LEARY, Times Staff Writer
© St. Petersburg Times
published December 22, 2002


CRYSTAL RIVER -- Every two years, Florida Power shuts down its nuclear reactor for a monthlong refueling process that is as complex as it is expensive.

This time, a $5-million, 83-ton hunk of steel is going to make things really tricky.

Like other utilities in the wake of a startling and potentially disastrous discovery at an Ohio plant this spring, Florida Power will replace the giant lid of its reactor in October.

Work already has begun. A site has been cleared for a building that will house the new lid, scheduled to arrive from France in early September, for final assembly.

"It will be like a big workshop," Florida Power spokesman Mac Harris said.

A second building, made of concrete, will be constructed in the spring for the old lid, which has been in service since the plant began making electricity in 1977.

The discarded head, which has been exposed to significant radiation, will be kept there until the plant is decommissioned. The license expires in 2016, but Florida Power will seek a 20-year extension from the Nuclear Regulatory Commission.

Concern over reactor lids stems in large part from a problem discovered early last spring at the Davis-Besse plant near Toledo.

In what has been called the nation's closest brush with a major nuclear accident since Three Mile Island in 1979, corrosive coolant ate a large hole (70 pounds in all) in the Davis-Besse lid.

The coolant -- boron mixed with water -- was able to seep through cracked nozzles that penetrate the lid and allow control rods to move up and down and manipulate the nuclear reaction.

Had it not been for a thin layer of stainless steel, the corrosive material could have eaten straight through the steel.

In that case, thousands of gallons of radioactive water would have spewed into the containment building, raising the risks of the core overheating, a meltdown and release of radiation.

Backup systems could be activated to pump more water into the reactor than was being allowed to escape, keeping the nuclear fuel safe until the reactor could be shut down.

But some industry watchdogs calling for more attention to the problem, including Union of Concerned Scientists, caution that those emergency systems or other plant equipment could be disrupted or damaged.

The discovery of the hole prompted the NRC to order the operators of 68 other pressurized-water reactors to report any signs of corrosion.

The NRC was previously aware problems could occur -- there had been less severe problems at plants in South Carolina and Arkansas -- and issued an advisory concerning cracking in August 2001.

In October of that year, Florida Power conducted an inspection during a planned maintenance outage. Workers discovered and repaired a circular crack around one of the 69 control rod nozzles, which allowed an unknown amount of coolant to leak from the vessel.

Plant officials said they found no other cracking or damage to the head. But in a report to the NRC after the Davis-Besse incident, Florida Power said it planned to replace the reactor lid in October 2003.

"The head was on order before Davis-Besse even occurred," Harris said.

Economics are driving the decision, officials said. The existing head design is prone to degradation and could cause problems. Also, the type of detailed inspections needed for nozzle cracking are expensive and time consuming.

"If you had a tire and you had to patch it and then you had to patch it again, there comes a time when it might be best to get a new tire," Harris said at the time.

So far, 25 nuclear plants have decided to replace their lids, according to the Nuclear Energy Institute, the industry lobbying group.

"I think you will see over time, more and more utilities doing that, especially those seeking license renewal," said Alex Marion, NEI's director of engineering.

He cautioned against drawing a conclusion that these other plants were in as much danger as Davis-Besse, owned by FirstEnergy Corp.

"The kind of corrosion that was found at Davis-Besse has not been found at any other plant, and all the plants have looked."

Lids cost about $5-million but engineering, shipping and other expenses put the total at roughly $25-million, according to the NEI. Florida Power would not disclose its cost.

The raw carbon steel form was forged in Japan and then shipped to a French company, Framatome, where engineers have done more detailed work, such as boring holes the control rods will penetrate and applying stainless steel cladding to the inner surface.

Harris said an improved metal alloy is being used in the lid to avoid problems plaguing older designs.

It is scheduled to arrive in Crystal River by early September. Then workers will perform final assembly and top the lid with a "service structure" that houses the control rod mechanisms. The service structure is being built in Virginia.

When fitted together, the equipment will be 35 feet high, 16 feet wide and weigh 150 tons.

Unlike some plants that will have to cut away concrete to install the reactor head, Florida Power's plant has a large enough equipment hatch on the side of the building.

The assembly building, which eventually will be torn down, is not vital, as the work could be done in the reactor building, Harris said. But it will allow the work to begin before refueling, avoiding a lengthier shutdown and minimizing workers' exposure to radiation.

-- Alex Leary can be reached at 564-3623 or leary@sptimes.com .

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