How to Tear Down a Nuclear Power Plant

How to Tear Down a
Nuclear Power Plant
What happens to nuclear reactors like those at Fukushima after
they melt down or reach the end of their useful lives?
By David Biello | Friday, April 29, 2011 | 5
GLOWING, GLOWING,
GONE: Because of the high
radiation levels around the
stricken Fukushima Daiichi
nuclear power plant work must
be done via remotely-operated
machines and workers must
wear full protective gear,
including breathing apparatus.
Image: Courtesy of TEPCO
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Twenty-five years after the tragic runaway fission and fire at
Chernobyl, tons of concrete shield workers and visitors from the
dangerously radioactive puddle of melted fuel that lurks in the basement of
the building housing reactor No. 4. Similarly, more than 30 years after the
partial meltdown at Three Mile Island in Pennsylvania, concrete shaved 2.5
centimeters deep guards a hollow reactor vessel, its partially melted down
fuel rods having been taken out over the course of a decade and shipped to
Idaho National Laboratory (INL) for study. And now, nearly two months
after the serial partial meltdowns in the reactors and spent-fuel pools at
Fukushima Daiichi, Tokyo Electric Power Co. (TEPCO) has announced at
least nine months of work to control the nuclear accident—the initial part of
a cleanup that could last for decades.
“It’s like mining,” says nuclear physicist Douglas Akers of INL of the
Three Mile Island cleanup effort. “Go in and remove the previously molten
fuel, pack it up in shipping containers, and remove it to Idaho.”
What happens when nuclear reactors reach the end of their useful
lives—either accidentally as in the cases above or as a planned shutdown for
a series of power plants throughout the U.S. and the world, more and more
in coming decades? The answer to that question ranges from a green field
suitable for farming to sacrificial zones that, in effect, become nuclear
parks, such as the 25-square-kilometer Rocky Flats National Wildlife
Refuge in Colorado—a former bomb-making site—or the 30-squarekilometer “exclusion zone” surrounding Chernobyl, respectively.
“Today we know that about 77,000 square miles of territory in
Europe and the former Soviet Union was contaminated with radioactive
fallout, leaving long-term challenges for flora, fauna, water, the
environment and human health,” wrote Mikhail Gorbachev, the Soviet
premier at the time of the Chernobyl explosion, in Bulletin of the Atomic
Scientists’s March/April 2011 issue. “Tens of billions of dollars have been
spent in trying to contain and remediate the disaster,” including a massive
sarcophagus currently being constructed to re-entomb the melted
radioactive fuel.
The cleanup at Fukushima Daiichi will face similar challenges,
including ascertaining how much of the nuclear fuel melted down and how
bad is the radioactive contamination on the power plant grounds—as well
as in surrounding areas. That challenge is exacerbated by the fact that three
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reactors and two spent fuel pools have been affected by the crisis but are
also surrounded by five further spent fuel pools and two more unaffected
reactors—and the fact that the fuel rods remain uncooled even today. Step
one will therefore be cooling the nuclear fuel, a process that could take at
least three months per TEPCO’s current plan, which involves entirely filling
the stricken reactors with seawater—although leaks may foil this plan.
View a slideshow of the plight of reactors at Fukushima Daiichi
“You have four reactors and you could easily have two or three
approaches to decommissioning,” says Kurt Kehler, vice president of
decommissioning and demolition at engineering company CH2M HILL,
whose company might bid for the job. “Some where the fuel melted, you
entomb. [There are] some where you can extract it and go into safe store,
and then some you could recover and keep operating.”
Decommissioning
Like many of the personnel operating the U.S. nuclear fleet, the name
for the end-of-life process for a nuclear power plant got its start in the U.S.
Navy—to decommission a reactor is to tear it down and restore its site to
one of several conditions within 60 years.
“Ideally for most utilities the intent is to remove everything from the
site and restore it to other uses than power generation,” says John
Hickman, project manager of the reactor decommissioning branch at the
U.S. Nuclear Regulatory Commission (NRC). Removal targets radioactive
contamination, be that the radioactive cobalt and cesium that typically
seeps into the concrete as a result of normal operations or plumes of water
contaminated with tritium—the radioactive form of hydrogen—that often
leaks from such power plants over the course of decades. Even so, tearing
apart a nuclear reactor does not mean undue exposure to radioactivity;
many forms of shielding—from concrete to cooling water itself—remain to
protect disassembly workers as well as specially designed tools, such as
particle-containment boxes for sawing through radioactive metals.
Right now, at least five such nuclear site decommissions are
underway in the U.S., ranging from Zion nuclear power plant in Illinois to
the cleanup of a sprawling nuclear bomb–making site at Hanford in
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Washington State. In the case of Zion nuclear waste disposal company
Energy Solutions has actually taken ownership of the former power plant,
through a subsidiary, and will tear it down in its entirety and ship all of the
resulting waste to Utah for disposal. Specially designated landfills, such as
Energy Solution’s site in western Utah or Barnwell nuclear dump in South
Carolina, hold the radioactive remnants from such deconstructions. “The
current estimate for the Zion facility—and the amount in the
[decommissioning] trust fund—is $900 million for this two-unit site,”
Hickman says. “The volume of material is enormous compared to past
decommissions.”
Energy Solutions takeover is a response to prior decommissionings,
such as Maine Yankee in the 1990s, which rapidly grew in expense as
workers attempted to sort radioactive material from its nonradioactive
counterparts. Like Zion, the Maine Yankee decommission aimed to restore
the site to a pristine condition, one in which a farmer could live on the
former nuclear power plant grounds, grow crops and eat them without an
“unacceptable dose” from any remaining radioactive contamination, says
NRC spokesman Scott Burnell.
There are other options, of course, such as Sacramento’s former
Rancho Seco nuclear power plant shut down in 1989, which has now been
turned into a solar farm and natural gas–fired generator. “Our regulations
require cleanup of the facility to the point that when they are done you can
only be exposed to 25 millirems per year from [nuclear power] plant–
generated materials,” Hickman says of that option. (A rem is a dosage unit
of x-ray and gamma-ray radiation exposure.) And, in the case of Three Mile
Island (TMI), reactor No. 2 will sit dormant until reactor No. 1 finishes its
useful life, in 2034, when both will be demolished. “The advantage of doing
it at that time is that any residual radioactivity associated with TMI reactor
No. 2 will have decayed quite a bit,” says Wayne Johnson, division manager
of the Earth Systems Science Division at Pacific Northwest National
Laboratory.
And there is often something left behind, at least in the U.S. where
there is no long-term repository for spent nuclear fuel. As a result, on each
and every decommissioned nuclear power plant site sit some number of
concrete and steel casks encasing the used uranium fuel rods. For example,
the Humboldt Bay nuclear power plant being torn down in California has a
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concrete pad with such cylinders sunk into it so they cannot tip over in an
earthquake. In addition, the pad is situated on a hill high enough to avoid a
tsunami. “The safety briefing is if the tsunami warning goes off, then run to
the top of where the spent fuel is because that’s the highest ground around,”
Hickman says.
In the case of Fukushima, it will be years before the uranium fuel
rods—if not too melted and deformed—are cool enough to be shifted to
such long-term storage. If the fuel rods are more melted, however, the
cleanup will be even more challenging, particularly if they have formed a
“puddle”. “You can’t very easily cool it off because you can’t get water to the
center,” notes nuclear physicist Douglas Akers of INL.
That makes it nearly impossible to remove, hence the puddle that sits
in the basement of Chernobyl. “Once you get fuel that is deformed or spread
like in Chernobyl, the risk to the worker and engineering controls that need
to be put in place to protect the worker become very expensive,” CH2M
HILL’s Kehler explains. “If there is a meltdown that is that extreme, then
you are looking at an entombment state for a number of years.” It remains
unclear exactly how melted the fuel in the three damaged reactors and two
crippled spent-fuel pools at Fukushima Daiichi are, although U.S. Secretary
of Energy Steven Chu estimated that as much as 70 percent of the fuel rods
may have melted.
At the same time, the puddle is relatively impervious. “It’s ceramic
armor surrounding fission by-products,” Akers says.
And then there are the sites that are really contaminated, like
Hanford in Washington State—some 1,500 square kilometers laced with the
residue of U.S. bomb-making operations stretching back to World War II.
“You hope that whoever left it for you cleaned it out,” says Kehler, whose
company is tasked with cleaning the site. “Sometimes they did and
sometimes they didn’t.”
Nuclear accident
Of course, even unregulated military sites for the production of
nuclear weapons often made at least some attempt to contain radioactive
material, including some of the most polluted sites in the world, which
Soviet technicians contaminated in pursuit of plutonium. That is not the
case for unplanned meltdowns, like the ones that ended the use of TMI
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reactor No. 2, Chernobyl reactor No. 4, and now Fukushima Daiichi reactor
Nos. 1, 2 and 3.
TMI was relatively easy to clean, thanks to safety systems that
contained most of the radioactive material. “Only 3 to 4 percent of the
reactor inventory [of radioactive noble gases*] was released,” Akers says,
and most of what did escape remained in the reactor buildings. “Effectively,
everything producing any off-site damage was all retained in the facility.”
But Fukushima and, even more so, Chernobyl saw the failure of such
safety systems to contain radioactive material and—in the case of
Chernobyl because of a fire—dispersal occurred over a wide area. Cleaning
that is impossible: “From a soil standpoint, there really is no [in-place]
treatment for radioactive contamination,” Kehler explains. “It’s either
removal or fix-in-place and control the footprint.” As a result, the
amoebalike contours of the exclusion zone in Ukraine and Belarus stretch
out around the remnants of the defunct nuclear power plant in Ukraine.
Something similar may happen in Fukushima given the dispersal of
radioactivity, including plutonium. Already, the Japanese government has
declared the region within 20-kilometers of the stricken nuclear power
plant a no-go zone, enforced by fines up to $1,200 and detention. And
although such plutonium is not in itself soluble in water, it is clear from
studies of heavily contaminated sites in Russia, such as former plutoniummaking facility known as Mayak, that plutonium and other insoluble
radioactive material tends to hitch a ride on tiny particles in the soil, known
as colloids.
Other radioactive material, such as cesium 137 with a half-life of
roughly 30 years, dissolves like salt in water, traveling into groundwater
supplies and even plants. Uptake by plants is a real concern for any nuclear
remediation, given the potential for human or animal consumption,
although some fungi seem to thrive on radioactive material. “The trouble
with particles with any living organism is breathing it, eating it, ingesting it,
getting it into the skin,” Kehler says. “A little bit of contamination can give a
big dose because it’s going to be there [inside] for a long time.”
But there are other biological responses: Cooling water from TMI
became a microbial farm—as is also likely to happen with the saltwater used
in the emergency at Fukushima. “They started growing algae and bacteria
in the reactor core,” Akers recalls. “It’s like a swimming pool that nobody’s
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cleaning up.”
What to do about the water?
Of course, dealing with contaminated water is a primary concern at
any defunct reactor site and the primary response is filtration, such as with
ion exchange columns that employ special resins to attract the radioactive
elements and pull them out of the water, often employed in series. “The
residual radioactive material itself [that is caught in those filters] is then
solidified in some way suitable for low-level waste disposal,” PNNL’s
Johnson explains. French nuclear giant Areva will employ such filtration
techniques to help decontaminate radioactive seawater at Fukushima
Daiichi.
In the case of TMI, after the water was filtered for heavier radioactive
isotopes, it was left to cool so that light radioactive isotopes like tritium—an
isotope of the hydrogen in water molecules—could break down. After 14
years, 8.7 million liters of it was simply allowed to evaporate. “They had the
option of either dumping it in the [Susquehanna] River or evaporating it,”
Akers says. “They chose to evaporate it.”
Tritium cannot be separated from water and has a half-life of more
than 12 years, although it emits relatively little harmful radiation when it
decays. TEPCO, in the case of Fukushima, will let some of the radioactive
seawater sit on its site in massive storage containers.
At the same time, TEPCO has already dumped 11,500 metric tons of
contaminated seawater into the ocean. That again will make radioactive
material available to sea life, potentially ending up in fish or marine
mammals that feed on them, based on previous such releases in the past.
That may alter such animals’ genetics as well as disrupt reproduction and
development, although the exact effects remain unclear for lack of study.
In the end such uptake by living organisms is the fate of all such
radioactive contamination in the wild. That’s why the greatest risk facing a
site like Chernobyl is something as natural as a wildfire, similar to the ones
that swept Russia and Ukraine this past summer. “One of the worst
accidents Chernobyl could have at this point is a forest fire,” Kehler notes.
“All the radioactivity in the plants would then become airborne.”
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*Correction (4/29/11): This sentence was edited after posting to note that
only noble gases escaped the reactor at Three Mile Island.
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