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03/29/2011

Long blackouts pose risk to US reactors

A power failure lasting for days at an American nuclear plant, whatever the
cause, could lead to a radioactive leak

 

By Dina Cappiello 
Associated Press

WASHINGTON -- Long before the nuclear emergency in Japan, U.S. regulators
knew that a power failure lasting for days at an American nuclear plant,
whatever the cause, could lead to a radioactive leak. Even so, they have
only required the nation's 104 nuclear reactors to develop plans for dealing
with much shorter blackouts on the assumption that power would be restored
quickly.

In one nightmare simulation presented by the Nuclear Regulatory Commission
in 2009, it would take less than a day for radiation to escape from a
reactor at a Pennsylvania nuclear power plant after an earthquake, flood or
fire knocked out all electrical power and there was no way to keep the
reactors cool after backup battery power ran out. That plant, the Peach
Bottom Atomic Power Station outside Lancaster, has reactors of the same
older make and model as those releasing radiation at Japan's Fukushima
Dai-ichi plant, which is using other means to try to cool the reactors.

And like Fukushima Dai-ichi, the Peach Bottom plant has enough battery power
on site to power emergency cooling systems for eight hours. In Japan, that
wasn't enough time for power to be restored. According to the International
Atomic Energy Agency and the Nuclear Energy Institute trade association,
three of the six reactors at the plant still can't get power to operate the
emergency cooling systems. Two were shut down at the time. In the sixth, the
fuel was removed completely and put in the spent fuel pool when it was shut
down for maintenance at the time of the disaster. A week after the March 11
earthquake, diesel generators started supplying power to two other two
reactors, Units 5 and 6, the groups said.

The risk of a blackout leading to core damage, while extremely remote,
exists at all U.S. nuclear power plants, and some are more susceptible than
others, according to an Associated Press investigation. While regulators say
they have confidence that measures adopted in the U.S. will prevent or
significantly delay a core from melting and threatening a radioactive
release, the events in Japan raise questions about whether U.S. power plants
are as prepared as they could and should be.

"We didn't address a tsunami and an earthquake, but clearly we have known
for some time that one of the weak links that makes accidents a little more
likely is losing power," said Alan Kolaczkowski, a retired nuclear engineer
who worked on a federal risk analysis of Peach Bottom released in 1990 and
is familiar with the updated risk analysis.

Risk analyses conducted by the plants in 1991-94 and published by the
commission in 2003 show that the chances of such an event striking a U.S.
power plant are remote, even at the plant where the risk is the highest, the
Beaver Valley Power Station in Pennsylvania.

These long odds are among the reasons why the United States since the late
1980s has only required nuclear power plants to cope with blackouts for four
or eight hours. That's about how much time batteries would last. After that,
it is assumed that power would be restored. And so far, that's been the
case.

Equipment put in place after the Sept. 11, 2001, terrorist attacks could buy
more time. Otherwise, the reactor's radioactive core could begin to melt
unless alternative cooling methods were employed. In Japan, the utility has
tried using portable generators and dumped tons of seawater, among other
things, on the reactors in an attempt to keep them cool.

A 2003 federal analysis looking at how to estimate the risk of containment
failure said that should power be knocked out by an earthquake or tornado it
"would be unlikely that power will be recovered in the time frame to prevent
core meltdown."

In Japan, it was a one-two punch: first the earthquake, then the tsunami.

Tokyo Electric Power Co., the operator of the crippled plant, found other
ways to cool the reactor core and so far avert a full-scale meltdown without
electricity.

"Clearly the coping duration is an issue on the table now," said Biff
Bradley, director of risk assessment for the Nuclear Energy Institute. "The
industry and the Nuclear Regulatory Commission will have to go back in light
of what we just observed and rethink station blackout duration."

David Lochbaum, a former plant engineer and nuclear safety director at the
advocacy group Union of Concerned Scientists, put it another way: "Japan
shows what happens when you play beat-the-clock and lose."

Lochbaum plans to use the Japan disaster to press lawmakers and the nuclear
power industry to do more when it comes to coping with prolonged blackouts,
such as having temporary generators on site that can recharge batteries.

A complete loss of electrical power, generally speaking, poses a major
problem for a nuclear power plant because the reactor core must be kept
cool, and back-up cooling systems -- mostly pumps that replenish the core
with water-- require massive amounts of power to work.

Without the electrical grid, or diesel generators, batteries can be used for
a time, but they will not last long with the power demands. And when the
batteries die, the systems that control and monitor the plant can also go
dark, making it difficult to ascertain water levels and the condition of the
core.

One variable not considered in the NRC risk assessments of severe blackouts
was cooling water in spent fuel pools, where rods once used in the reactor
are placed. With limited resources, the commission decided to focus its
analysis on the reactor fuel, which has the potential to release more
radiation.

An analysis of individual plant risks released in 2003 by the NRC shows that
for 39 of the 104 nuclear reactors, the risk of core damage from a blackout
was greater than 1 in 100,000. At 45 other plants the risk is greater than 1
in 1 million, the threshold NRC is using to determine which severe accidents
should be evaluated in its latest analysis.

The Beaver Valley Power Station, Unit 1, in Pennsylvania had the greatest
risk of core melt -- 6.5 in 100,000, according to the analysis. But that
risk may have been reduced in subsequent years as NRC regulations required
plants to do more to cope with blackouts. Todd Schneider, a spokesman for
FirstEnergy Nuclear Operating Co., which runs Beaver Creek, told the AP that
batteries on site would last less than a week.

In 1988, eight years after labeling blackouts "an unresolved safety issue,"
the NRC required nuclear power plants to improve the reliability of their
diesel generators, have more backup generators on site, and better train
personnel to restore power. These steps would allow them to keep the core
cool for four to eight hours if they lost all electrical power. By contrast,
the newest generation of nuclear power plant, which is still awaiting
approval, can last 72 hours without taking any action, and a minimum of
seven days if water is supplied by other means to cooling pools.

Despite the added safety measures, a 1997 report found that blackouts -- the
loss of on-site and off-site electrical power -- remained "a dominant
contributor to the risk of core melt at some plants." The events of Sept.
11, 2001, further solidified that nuclear reactors might have to keep the
core cool for a longer period without power. After 9/11, the commission
issued regulations requiring that plants have portable power supplies for
relief valves and be able to manually operate an emergency reactor cooling
system when batteries go out.

The NRC says these steps, and others, have reduced the risk of core melt
from station blackouts from the current fleet of nuclear plants.

For instance, preliminary results of the latest analysis of the risks to the
Peach Bottom plant show that any release caused by a blackout there would be
far less rapid and would release less radiation than previously thought,
even without any actions being taken. With more time, people can be
evacuated. The NRC says improved computer models, coupled with up-to-date
information about the plant, resulted in the rosier outlook.

"When you simplify, you always err towards the worst possible circumstance,"
Scott Burnell, a spokesman for the Nuclear Regulatory Commission, said of
the earlier studies. The latest work shows that "even in situations where
everything is broken and you can't do anything else, these events take a
long time to play out," he said. "Even when you get to releasing into
environment, much less of it is released than actually thought."

Exelon Corp., the operator of the Peach Bottom plant, referred all detailed
questions about its preparedness and the risk analysis back to the NRC. In a
news release issued earlier this month, the company, which operates 10
nuclear power plants, said "all Exelon nuclear plants are able to safely
shut down and keep the fuel cooled even without electricity from the grid."

Other people, looking at the crisis unfolding in Japan, aren't so sure.

In the worst-case scenario, the NRC's 1990 risk assessment predicted that a
core melt at Peach Bottom could begin in one hour if electrical power on-
and off-site were lost, the diesel generators -- the main back-up source of
power for the pumps that keep the core cool with water -- failed to work and
other mitigating steps weren't taken.

"It is not a question that those things are definitely effective in this
kind of scenario," said Richard Denning, a professor of nuclear engineering
at Ohio State University, referring to the steps NRC has taken to prevent
incidents. Denning had done work as a contractor on severe accident analyses
for the NRC since 1975. He retired from Battelle Memorial Institute in 1995.


Associated PressCopyright 2010 Associated Press. All rights reserved. This
material may not be published, broadcast, rewritten, or redistributed.

"They certainly could have made all the difference in this particular case,"
he said, referring to Japan. "That's assuming you have stored these things
in a place that would not have been swept away by tsunami." 

 



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