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Corrosion Find At TVA's Sequoyah Prompts New Inspections
DOW JONES NEWSWIRES
NEW YORK -- The Tennessee Valley Authority said Thursday that recent inspections turned up worrisome signs of corrosion on part of the reactor vessel head at its Sequoyah Nuclear Plant Unit 1, which had been considered among the reactors least-susceptible to the kind of leakage that causes decay.
The utility told federal nuclear regulators Wednesday that tests had confirmed that a buildup of crystals on the vessel head found during recent visual inspection contained boron. Boron, which is used in the reactor cooling system, has been linked to corrosion-related cracking at several U.S. pressurized water reactors.
TVA spokeswoman Lucha Ramey said the utility has hired Framatome ANP, a unit of the French nuclear firm Areva (F.ARV) and Germany's Seimens AG (SI), to conduct additional non-visual tests of the reactor vessel head.
The utility told the Nuclear Regulatory Commission that the boron leak was probably coming from a crack in one of the sleeve-like nozzles that allow control rods to enter the reactor. The nozzles are made of a nickel alloy that over time tends to crack.
Sequoyah Unit 1, located near Chatanooga, Tenn., has been in a scheduled refueling and maintenance outage since mid-March that has included a federally-mandated visual inspection of the top of the reactor.
Ramey said she didn't know if the additional inspections would extend the outage. The outage was expected to last about 75 days while operators replaced four massive 360-ton steam generators at a cost of $160 million to $200 million. The old steam generators had stress cracks in tubes made of the same nickel alloy found in nozzles.
Corrosion caused by boric acid is the Achilles' heel of pressurized water reactors and has cost reactor owners millions to fix.
Boric acid was responsible for eating a 30 square-inch hole in the reactor vessel head at FirstEnergy Corp.'s (FE) Davis-Besse plant in Oak Harbor, Ohio.
Last March, during a routine inspection operators found several nozzle cracks including one that leaked enough acid to eat through the six-inch thick carbon steel cap, down to the reactor's thin stainless steel inner liner.
As a result of that find, the NRC in February ordered the nation's 69 pressurized water reactors to submit to regular visual and non-visual tests based on a susceptibility ranking.
Sequoyah was ranked among the least susceptible to acid corrosion, but that could change if the Framatome inspections confirm there is a crack in the control rod nozzle, said NRC spokesman Scott Burnell.
"They need to go ahead and finish the testing to figure out where the leak is," Burnell said. "But if it turns out to be a crack in the control rod drive mechanism nozzle it would put them in the high susceptibility category."
If that's the case, TVA would be required to conduct in-depth tests during every refueling outage at the unit.
The costs of those tests are high enough that at least 21 of the 28 reactors in the high susceptibility category are scheduled to have new reactor vessel heads installed.
Ramey said the utility would address the question of whether or not to replace the head once the results of the test are in.
She added that there hadn't been any sign of leakage during the unit's most recent operating cycle.
TVA is the nation's largest public power producer. In addition to the two-unit Sequoyah plant, it operates the two-unit Browns Ferry plant near Athens, Ala. and the single-unit Watts Bar plant near Spring City, Tenn.
-By Jennifer Morrow, Dow Jones Newswires; 201-938-4377; jennifer.morrow@dowjones.com
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Updated March 27, 2003 2:53 p.m.
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