April 24, 2014 – Would the Fukushima Daiichi disaster have unfolded differently had the nuclear plant been built on a floating platform, similar to those used for offshore oil drilling?

When an earthquake and tsunami struck the Fukushima Daiichi nuclear plant complex in 2011, neither the quake nor the inundation caused the ensuing contamination. Instead, it was the aftereffects—specifically, the lack of cooling for the reactor cores due to a loss of all power at the station—that caused most of the harm.

A new design for nuclear plants built on floating platforms could help avoid such consequences in the future. Such 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 and the escape of radioactive material.

This concept was ‘floated’ (pardon the pun) at the Small Modular Reactors Symposium by MIT professors Jacopo Buongiorno, Michael Golay and Neil Todreas, along with others from MIT, the University of Wisconsin, and Chicago Bridge and Iron (a nuclear plant and offshore platform construction company).

Such plants, Buongiorno explained, could be built in shipyards 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 & gas drilling platforms. Using established designs minimizes technological risks, said Buongiorno.

Although the concept of a floating nuclear plant is not unique [apparently Russia is in the process of building one on a barge moored at the shore], none have been located far enough offshore to be able to ride out a tsunami, Buongiorno said. For this new design, “the biggest selling point is the enhanced safety”.

A floating platform several miles offshore, moored in about 100 metres of water, would be unaffected by the motions of a tsunami; earthquakes would have no direct effect at all. Meantime, the biggest issue that faces most nuclear plants under emergency conditions—overheating and potential meltdown (e.g. Fukushima, Chernobyl, Three Mile Island) would be virtually impossible at sea, Buongiorno concluded. “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.”

Buongiorno listed several other advantages. For one, 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 centres they serve. “The ocean is inexpensive real estate,” notes Buongiorno.

At the end of a plant’s life, 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.

This design could also help to address practical construction issues that have tended to make new nuclear plants uneconomical, added Buongiorno; shipyard construction allows for better standardization, and the all-steel design eliminates the use of concrete, which Buongiorno said is often responsible for construction delays and cost overruns.

There are no particular limits to the size of such plants, he went on: they could be anywhere from 50MW to 1000MW.

— With files from David Chandler, MIT News Office.

Photo 1: This illustration shows a possible configuration of a floating offshore nuclear plant, based on design work by Jacopo Buongiorno and others at MIT’s Department of Nuclear Science and Engineering. Like offshore oil drilling platforms, the structure would include living quarters and a helipad for transportation to the site.

Photo 2: Cutaway view of the proposed plant shows that the reactor vessel itself is located deep underwater, with its containment vessel surrounded by a compartment flooded with seawater, allowing for passive cooling even in the event of an accident.