Three years ago, the safety of nuclear reactors, a staple and stable source of base load power for many industrialized countries, was suddenly thrown into question, after a 15-metre wall of sea water inundated three nuclear reactors at the Fukushima Daiichi power plant in Japan, causing them to overheat.
The reactors were built to withstand earthquakes but not the height of the surging waves. Backup power was available to run the cooling pumps, but when the tsunami flooded the site, the pumps lost power and thus, the ability to circulate water and cool the reactor cores. The resultant fuel meltdown and leakage of radiation led to the immediate evacuation of the site, and a chain of events that eventually had Japan shutting down all of its still-functioning nuclear reactors. Germany, a major consumer of nuclear power, permanently closed eight of its 17 nuclear reactors following Fukushima; other European countries shelved their nuclear plans. Nuclear power, it seemed, was on its knees.
While nuclear proponents view Fukushima as an aberration and trust that nuclear is safe, opponents hold up Fukushima and other major accidents such as Three Mile Island as exemplifying the perils of land-based nuclear power generation.
Now another option is being presented by researchers at MIT, the University of Wisconsin and Chicago Bridge & Iron, a multinational construction company. The team have come up with a new type of nuclear reactor that floats at sea. Led by Jacopo Buongiorno, an associate professor of nuclear science and engineering, the concept is a nuclear power plant built on a floating platform similar to an offshore oil rig. The plant would be manufactured at a shipyard then towed out to sea, where it would be anchored to the ocean bottom. An underwater cable would transmit electricity back to land, and there would be a living quarters built into the plant, just like an offshore drilling platform. The reactor pressure vessel – the part of the reactor susceptible to overheating – would be surrounded by a containment vessel, and flooded with seawater.
The amount of power the reactors would produce is small compared to a regular reactor- just 300 megawatts. In the United States, the smallest reactor is 502 MW, and the largest is the Palo Verde plant in Arizona, whose three reactors crank out a combined capacity of around 3,937 MW, according to the U.S. Energy Information Administration.
While the concept for a floating nuclear reactor isn't entirely new- Russia is already building one and planning to put it into service by 2016 – the MIT-led prototype is the first to combine a nuclear power plant with an oil drilling platform in its design. Also, unlike the Russian plant, which is located very close to shore, OSMRs (Offshore Small Modular Reactors) would be towed far out to sea.
Presenting the idea at a recent conference, MIT researchers say that OSMRs offer several advantages over traditional land-based nuclear power plants. First, being located far from land in deep ocean would make the reactors less vulnerable to earthquakes and tsunami waves, because the waves would be smaller than when they crest on land, and seismic waves would be absorbed by the ocean.
Second, with seawater employed as a coolant, the potential for meltdowns would be dramatically reduced.
"The ocean itself can be used as an infinite heat sink," Prof. Buongiorno says in a video describing the technology. "The decay heat, which is generated by the nuclear fuel even after the reactor is shutdown, can be removed indefinitely."
Third, the small floating reactors could be scaled up or moved around to areas considered vulnerable to tsunamis, such as Southeast Asia, or where there are limited energy resources but large coastal populations. They could also be towed ashore and decommissioned once they reach the end of their lives.
While the pros of OSMRs do appear to outweigh the cons, there are some unanswered questions. One is what would happen to the surrounding marine life should an uncontained nuclear meltdown occur at sea. Who can forget the Google Earth map depicting a yellow-green plume of radiation stretching half-way across the Pacific? While the authenticity of the map was later questioned, scientists have discovered trace amounts of radiation on the North American West Coast, a full three years after the event.
Another is the threat of terrorism. The MIT researchers claim that offshore nukes would be harder to attack, but on the other hand, they would also be tough to defend. Todd Woody, writing for The Atlantic, observed that defending these "nuclear islands" from terrorist assault, by ships and submarines, "would require some James Bond-like machinations," including early detection systems, barriers to vital access points, and the use of automatic weaponry.
None of that, however, should dampen enthusiasm for an idea whose time may have come in this post-Fukushima world. We already have the technology to mine asteroids, map the ocean floor to discover a missing jetliner, and fly civilians to the moon. If the technology can be de-risked, floating nuclear power plants could help to rebuild public trust in a form of energy whose image has been badly bruised.
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Written by Andrew Topf at Oilprice.com.