WASHINGTON (AP) — The risk that an earthquake would cause a severe accident
at a U.S. nuclear plant is greater than previously thought, 24 times as high
in one case, according to an AP analysis of preliminary government data. The
nation’s nuclear regulator believes a quarter of America’s reactors may need
modifications to make them safer.
The threat came into sharp focus last week, when shaking from the largest
earthquake to hit Virginia in 117 years appeared to exceed what the North
Anna nuclear power plant northwest of Richmond was built to sustain.
The two North Anna reactors are among 27 in the eastern and central U.S.
that a preliminary Nuclear Regulatory Commission review has said may need
upgrades. That’s because those plants are more likely to get hit with an
earthquake larger than the one their design was based on. Just how many
nuclear power plants are more vulnerable won’t be determined until all
operators recalculate their own seismic risk based on new assessments by
geologists, something the agency plans to request later this year. The NRC
on Thursday issued a draft of that request for public comment.
The review, launched well before the East Coast quake and the Japan nuclear
disaster in March, marks the first complete update to seismic risk in years
for the nation’s 104 existing reactors, despite research showing greater
The NRC and the industry say reactors are safe as they are, for now. The
average risk to U.S. reactors of core damage from a quake remains low, at
one accident every 500 years, according to the AP analysis of NRC data.
But emails obtained in a more than 11,000-page records request by The
Associated Press show that NRC experts were worried privately this year that
plants needed stronger safeguards to account for the higher risk
The nuclear industry says last week’s quake proved reactors are robust. When
the rumbling knocked out off-site power to the North Anna plant in Mineral,
Va., the reactors shut down and cooled successfully, and the plant’s four
locomotive-sized diesel generators turned on. The quake also shifted about
two dozen spent fuel containers, but Dominion Virginia Power said Thursday
that all were intact.
Still, based on the AP analysis of NRC data, the plant is 38 percent more
likely to suffer core damage from a rare, massive earthquake than it
appeared in an analysis 20 years ago.
That increased risk is based on an even bigger earthquake than the one last
week. Richard Zuercher, a spokesman for Dominion, the plant operator, says
the earlier estimate “remains sound because additional safety margin was
built into the design when the station was built.”
The safety cushion would shrink, though, if the plant’s risk is found to be
Federal scientists update seismic assessments every five to six years to
revise building codes for some structures. But no similar system is in place
for all but two of the nation’s 104 reactors — even though improving
earthquake science has revealed greater risks than previously realized.
The exception is Diablo Canyon in earthquake-prone California, which has
been required to review the risk of an earthquake routinely since 1985. The
NRC does not require plants to re-examine their seismic risks to renew
operating licenses for 20 years.
After the March earthquake in Japan that caused the biggest nuclear crisis
since Chernobyl, NRC staffers fretted in emails that the agency’s
understanding of earthquake risk for existing reactors was out of date.
In a March 15 email, for example, an NRC earthquake expert questioned
releasing data to the public showing how strong an earthquake each plant was
designed to withstand. The seismologist, Annie Kammerer, acknowledged that
recent science showed stronger quakes could happen. “Frankly, it is not a
good story for us,” she wrote to agency colleagues.
Kammerer’s boss, Brian Sheron, who heads the NRC’s Office of Nuclear
Regulatory Research, wrote in a March 14 email that updated numbers showed
the government “didn’t know everything about the seismicity” in the central
and the eastern part of the country.
“And isn’t there a prediction that the West Coast is likely to get hit with
some huge earthquake in the next 30 years or so? Yet we relicense their
plants,” he wrote.
The NRC flagged the 27 plants for possible upgrades by calculating the
likelihood of a severe accident based on 2008 hazard maps from the U.S.
Geological Survey and comparing it to the seismic risk estimated in 1989 or
1994. Those data were used the last time existing reactors evaluated their
The NRC identified the 27 reactors with the greatest risk increase but did
not provide the risk numbers. The AP used the NRC’s data and methodology to
calculate the risk increase for each reactor.
The Perry 1 reactor in Ohio tops the list with the steepest rise in the
chance of core damage: 24 times as high as thought in 1989. The four other
plants with the largest increases include River Bend 1 in Louisiana, up nine
times; Dresden 2-3 in Illinois, eight times; Farley 1-2 in Alabama, seven
times, and Wolf Creek 1 in Kansas, also seven times. The smallest increase
was the 38 percent at North Anna.
Todd Schneider, a spokesman for First Energy Corp., which operates the Perry
plant, said the increase in its seismic risk estimated by the NRC is
misleading. He said Perry is capable of withstanding an even larger
earthquake than is typical for the region.
Personnel at a handful of other plants, including Indian Point outside New
York City and Oconee in South Carolina, have already redone the NRC’s
calculations, and they show a much lower risk of core damage from
earthquakes. Those calculations have not yet been reviewed by the agency,
which along with other federal agencies is developing a baseline earthquake
risk for every nuclear power plant to use.
Predicting earthquake probability and damage is dicey; the Japanese nuclear
industry was taken by surprise in March when a quake-driven tsunami far
surpassed predictions and swamped the Fukushima Dai-ichi site.
The U.S. nuclear industry may not be fully ready, either. Current
regulations don’t require the NRC to make sure nuclear reactors are still
capable of dealing with a new understanding of the threats.
It’s not just earthquakes. It is all types of events, including floods,
tornadoes and hurricanes, said an NRC official, who spoke on condition of
anonymity because he was not authorized to speak about the agency’s recent
The worry about earthquakes is not so much direct damage to the reactor
vessel, the hardened enclosure where the nuclear reaction takes place, but
to water tanks and mechanical and electrical equipment needed when disaster
strikes. The failure of those systems could disable cooling needed to
prevent meltdowns of radioactive fuel.
In some of the emails obtained by the AP, NRC staffers worried that U.S.
reactors had not thoroughly evaluated the effects of aftershocks and the
combined impact of a tsunami and earthquake. They suggested plants might
need more durable piping as well as better flood barriers and waterproof
storage of essential equipment. Staffers talked of a need for bigger
supplies of fuel and batteries for extended losses of all electrical power.
One email expressed concern about some key pumps at Dresden that might fail
in an earthquake.
In a separate problem reported last month, GE Hitachi Nuclear Energy
acknowledged that its older control rods could get stuck if an earthquake
struck when reactors were running at low power. Control rods are needed to
stop the nuclear reaction. The manufacturer has alerted the operators of 35
U.S. reactors at 24 sites, who are checking whether replacements are needed.
The AP documented scores of instances of such wear and tear in a range of
equipment in a June investigative series showing that safety standards have
been relaxed to keep aging reactors within the rules.
When the NRC ran preliminary calculations of quake risk last year, it was
the first time the agency had reassessed the threat since most plants were
“The plants were more vulnerable than they realized, but they weren’t
unsafe. We look at rare, rare events,” said Kammerer, the NRC seismologist.
Plants built a generation ago were designed to withstand an earthquake
larger than any known to have occurred in the area. But since then,
scientists have been able to better estimate the earthquakes that are
possible. And in some cases, those rare quakes could be larger and more
frequent than those the plants were designed for.
“If they met a certain level, they didn’t look any further,” Gregory Hardy,
an industry consultant at Simpson, Gumpertz and Hegger in Newport Beach,
Calif., said of some of the industry’s earlier assessments. “Forty years
ago, when some of these plants were started, the hazard — we had no idea. No
Seismologists inside the agency didn’t recognize that increasing earthquake
risk was an issue until operators started applying to build new reactors at
existing plant sites in the central and eastern United States in 2003. Those
applications included a thorough analysis of the risk posed by earthquakes,
which is required for all new nuclear power plants.
In some cases, the result was much higher than risk calculations performed
by the industry in the early 1990s as part of a broader assessment of
“We did have some idea that the hazard was going up” in the period between
the late 1990s analysis and the applications for new reactors, said Clifford
Munson, a senior technical adviser in the NRC’s Office of Nuclear Reactors.
But Munson said some of the research indicated that there was disagreement
on whether the ground motion predicted would damage nuclear power plants.
Kamal Manoly, another NRC senior technical adviser, said, “There was nothing
alarming (enough) for us to take quick action.”
But a task force requested by President Barack Obama to make U.S. safety
recommendations after the Japanese accident has questioned that. Its
three-month review concluded that existing reactors should re-examine their
earthquake risk more often.
Some operators are expressing caution about the NRC’s initial analysis, and
say their own early calculations show that their facilities are at much
lower risk. The differences between the calculations of government and
industry have prompted some to call for a third-party review.
“It sort of defies logic to ask the regulated entity to do the seismic
analysis to determine whether upgrades are necessary or relicensing is
appropriate,” said California Sen. Sam Blakeslee, a geophysicist who pushed
a bill through the Legislature giving the California Energy Commission a
role in assessing seismic risk, particularly at Diablo Canyon. “There needs
to be a more arm’s length relationship in getting this technical
There will always be uncertainties, experts say.
“If all these plants were subjected to large earthquakes, that’s the only
way anybody can say for sure. But the only ones we know of are in Japan,”
said Hardy, referring to the quake that struck in March and another in 2007
that damaged the Kashiwazaki-Kariwa nuclear power plant.
“There is a pretty good technical feeling that U.S. plants are going to be
safe,” Hardy said, “but there is just a question of how much work it will
take to show it.”