When an earthquake and tsunami struck the Fukushima Daiichi
nuclear plant complex in 2011, neither the quake nor the inundation caused the
ensuing contamination. Rather, it was the aftereffects -- specifically, the
lack of cooling for the reactor cores, due to a shutdown of all power at the
station -- that caused most of the harm.
A new
design for nuclear plants built on floating platforms, modeled after those
used for offshore oil drilling, could help avoid such consequences in the
future. Such floating plants would be designed to be automatically cooled by
the surrounding seawater in a worst-case scenario, which would indefinitely
prevent any melting of fuel rods, or escape of radioactive material.
The concept is being presented this week
at the Small Modular Reactors Symposium, hosted by the American Society of
Mechanical Engineers, by MIT professors along with others from MIT, the
University of Wisconsin, and Chicago Bridge and Iron, a major nuclear plant and
offshore platform construction company.
Such plants could be built in a shipyard,
then towed to their destinations five to seven miles offshore, where they would
be moored to the seafloor and connected to land by an underwater electric
transmission line. The concept takes advantage of two mature technologies:
light-water nuclear reactors and offshore oil and gas drilling platforms. Using
established designs minimizes technological risks, says professor of nuclear
science and engineering (NSE) at MIT.
Although the concept of a floating nuclear
plant is not unique -- Russia is in the process of building one now, on a barge
moored at the shore -- none have been located far enough offshore to be able to
ride out a tsunami. For this new design, "the biggest selling point is the
enhanced safety."
A floating platform several miles
offshore, moored in about 100 meters of water, would be unaffected by the
motions of a tsunami; earthquakes would have no direct effect at all.
Meanwhile, the biggest issue that faces most nuclear plants under emergency
conditions -- overheating and potential meltdown, as happened at Fukushima,
Chernobyl, and Three Mile Island -- would be virtually impossible at sea, Professor
says: "It's very close to the ocean, which is essentially an infinite heat
sink, so it's possible to do cooling passively, with no intervention. The
reactor containment itself is essentially underwater."
List of several other advantages. For one thing, it is increasingly difficult and expensive to
find suitable sites for new nuclear plants: They usually need to be next to an
ocean, lake, or river to provide cooling water, but shorefront properties are
highly desirable. By contrast, sites offshore, but out of sight of land, could
be located adjacent to the population centers they would serve. "The ocean
is inexpensive real estate.
In addition, at the end of a plant's
lifetime, "decommissioning" could be accomplished by simply towing it
away to a central facility, as is done now for the Navy's carrier and submarine
reactors. That would rapidly restore the site to pristine conditions.
This design could also help to address
practical construction issues that have tended to make new nuclear plants
uneconomical: Shipyard construction allows for better standardization, and the
all-steel design eliminates the use of concrete, which is often responsible for
construction delays and cost overruns.
There are no particular limits to the size
of such plants. They could be anywhere from small, 50-megawatt plants to
1,000-megawatt plants matching today's largest facilities. "It's a
flexible concept,".
Most operations would be similar to those
of onshore plants, and the plant would be designed to meet all regulatory
security requirements for terrestrial plants. "Project work has confirmed
the feasibility of achieving this goal, including satisfaction of the extra
concern of protection against underwater attack.
Market
for such plants in Asia, which has a combination of high tsunami risks and a
rapidly growing need for new power sources. "It would make a lot of sense
for Japan," he says, as well as places such as Indonesia, Chile, and
Africa
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