Earthquake risk at TVA nuclear plants upgraded
Nuclear plants safe despite new seismic maps, TVA says
TVA says its Sequoyah Nuclear Plant in Soddy-Daisy, Tenn., is designed for a 5.8-magnitude earthquake. Last month's earthquake in Japan was 9.0. / ASSOCIATED PRESS
New seismic information shows that the risk of earthquakes damaging many of the country's nuclear plants — including TVA's — is higher than had once been estimated.
The Nuclear Regulatory Commission says that the shift is incremental and that all of the nation's plants remain safe despite the new data.
"There is no plant in this country where the information changed enough to make us have any question about the current safety margin," said Roger Hannah, an NRC spokesman in Atlanta.
Still, the report raises new questions in light of the earthquake- and tsunami-damaged nuclear reactors in Japan and the Tennessee Valley Authority's aggressive push toward more nuclear power.
The higher damage estimate "is large enough to warrant continued evaluation" for about one-fourth of the operating plants in the country, an August NRC report concluded.
There are 27 plants on the list, including TVA's Sequoyah and Watts Bar nuclear plants in Tennessee, where the NRC report shows that earthquake risks are five to six times greater than previously thought.
TVA says it is prepared.
"We are designed for the worst-ever-seen earthquake in the eastern part of the United States and a margin factor 10 times higher," said Preston Swafford, TVA's chief nuclear officer.
Nevertheless, TVA and owners of other plants will be asked to reassess their reactors to determine whether something might need to be done differently, such as more frequent inspections or retrofits to improve safety.
"We'll see if there are things plants may be able to do to increase the safety margin without spending billions of dollars," Hannah said. "It's like designing a car. Obviously, you can always make things a little bit safer, but you reach a certain point where each incremental gain in safety is unbelievably expensive."
Since the disaster in Japan, all plants in the United States will be re-evaluated, he said.
Odds are 1 in 19,608 each year that TVA's Sequoyah plant, about 18 miles northeast of Chattanooga, would have an earthquake strong enough to damage a reactor's core, the NRC report shows in one model. That compares with a 1-in-102,041 chance calculated from data two decades earlier.
The odds for two of the three reactors at Browns Ferry, 100 miles south of Nashville, shifted to 1 in 185,185, compared with 1 in 625,000. The third and oldest reactor moved to a 1-in-270,270 chance from 1 in 1 million.
At Watts Bar, about 60 miles southwest of Knoxville, the new estimate was 1 in 27,778, compared with 1 in 178,571 before.
The NRC report resulted in a controversial ranking that placed three of TVA's six reactors in the top quarter for risk of earthquake damage among the nation's 104 commercial electricity-producing reactors.
Sequoyah's two reactors landed in the fifth-highest risk slot when investigative reporter Bill Dedman with msnbc.com used the NRC's data to do the ranking.
Watts Bar, which has one reactor and another under construction, came in at No. 24. Two of Browns Ferry's three reactors were listed at No. 86, and the oldest reactor there was at 94.
The rankings created a flurry of complaints from the nuclear industry.
"We would refute that," said Ray Golden, a TVA spokesman. "The NRC has refuted that. There is no ranking system that ranks nuclear plants' risks."
Dedman had rearranged the data in the NRC's report so that the reactors, instead of being alphabetized by name, were listed in order of the NRC's estimates of earthquake risk.
The federal agency has found no errors in the data that Dedman used, according to Hannah. The objection is to using the data to rank the plants.
"It was not the intent of those numbers, nor was it something you could use those numbers for," Hannah said. "The list was developed to decide which plants to evaluate first."
Though TVA officials don't agree with his report, Golden said: "I don't want to downplay what he has found there, and that is that, in fact, the NRC and the industry continually looks at seismic information as it becomes available."
The hazard estimates are for the reactor cores, which heat up in a highly radioactive process as atoms split. The purpose is to turn water into steam to generate electricity.
The report said that the estimated seismic hazard levels at some sites might be higher than what had been considered when the plants were designed and built.
Hannah said that even so, the staff believes the plants were built conservatively enough — with an eye to the potential for larger earthquakes than expected — that they are safe.
Science evolves
The data change came about because the U.S. Geological Survey updates its seismic hazard maps every several years, using improved technologies and new information.
Changes to seismic hazard maps are to be expected regularly because earthquake science is still young, said Paul Caruso, a geophysicist with the USGS.
The NRC did its August 2010 report based on 2008 maps.
Some of the analyses "were very conservative, making the calculated risk higher than reality," according to an NRC fact sheet written for the public.
The major change for TVA's reactors came about because of a strip running through East Tennessee where the USGS concluded more earthquake activity could be expected. The New Madrid seismic zone running along western Tennessee and eastern Missouri was already known to be a likely spot for a major quake.
The state's history is rich with past quakes, including a series in 1811 through 1812 that caused the Mississippi River to back up and form Reelfoot Lake in West Tennessee. Those quakes, centered in Missouri, had an estimated magnitude of 8 or greater on the Richter scale.
A few large and many small tremors have struck the state since then, including as recently as 10 days ago.
A small quake centered near Maryville, about 50 miles from TVA's Watts Bar Plant, caused minor tremors on March 24, as did another on March 23, about 15 miles from TVA's Browns Ferry plant.
"We don't feel them," TVA's Golden said of the small ones.
Mild tremors are common, and TVA has monitors at its plants to alert operators in the case of a larger earthquake that might warrant shutting down the reactors, he said.
Browns Ferry is designed to withstand at least an earthquake that's a 6 on the Richter scale, and Sequoyah and Watts Bar are built for at least 5.8, he said.
Japan's reactors were designed for 7 to 8, he said, and still could handle what has been calculated as a 9. The tsunami, not the quake itself, has been blamed for most of the problems.
Industry is challenged
Calls have been made for a halt to new nuclear reactor construction in this country from groups that include the Blue Ridge Environmental Defense League and the Bellefonte Efficiency and Sustainability Team.
TVA has spent millions of dollars looking into whether it might resume construction at its Bellefonte site in northern Alabama.
Two semi-completed 1970s-era reactors have been mothballed there for years amid questions about costs, safety and whether the power was needed. TVA asked in 2008 to have its construction permit reinstated.
Several countries, most recently Italy, have put moratoriums on new nuclear plants or are otherwise stepping back from nuclear power until more is known about what happened in Japan.
On Tuesday, U.S. Rep. Edward Markey, D-Mass., introduced legislation in Congress calling for a moratorium on licensing of new nuclear plants in this country.
The Nuclear Energy Institute, the main industry association, has responded that nuclear plants, which provide 20 percent of the country's electricity, are safe and that this is unnecessary.
Marvin Fertel, NEI president and chief executive officer, said the NRC has processes in place to review new information that may arise during construction.
He advised in a statement released last week that the NRC, an independent regulator, should be left to handle the matter.
TVA board to meet
TVA has been left in the somewhat awkward position of having declared before the Japanese disaster that it wants to be the leader in new nuclear development in this country.
So far, it's not backing off.
Still, TVA board Chairman Dennis Bottorff said the April 14 board meeting will include much discussion of the issue.
The Japanese reactors are of the same General Electric Mark 1 design as TVA's three Browns Ferry reactors.
After the earthquake and tsunami overwhelmed the reactors in Japan, a complete power shutdown occurred, leading to hydrogen explosions, dangerous overheating and radiation releases.
The TVA reactors contain additional safeguards to maintain power and cooling systems, officials said. They showed off some of those on a tour March 25 at Browns Ferry. Among the backups were large generators with diesel supplies at the ready in plant areas said to be watertight.
TVA officials say they are well prepared for severe floods as well as earthquakes at all of their reactors.
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