In the aftermath of the Fukushima disaster in March, the appetite for new nuclear power plants slipped to post-Chernobyl lows. Regulators from Italy to Switzerland to Texas moved to stop pending nuclear-power projects, and the U.S. Nuclear Regulatory Commission (NRC) began to reevaluate the safety of all domestic plants. Yet nuclear power still provides 20 percent of America’s total electric power and 70 percent of its emissions-free energy, in large part because no alternative energy source can match its efficiency.
One nuclear plant with a footprint of one square mile provides the energy equivalent of 20 square miles of solar panels, 1,200 windmills or the entire Hoover Dam. If the country wants to significantly reduce its dependence on carbon-based energy, it will need to build more nuclear power plants. The question is how to do so safely.
In the 30 years since regulators last approved the construction of a new nuclear plant in the U.S., engineers have improved reactor safety considerably. (You can see some of the older, not-so-safe ones in this sweet gallery.) The newest designs, called Generation III+, are just beginning to come online. (Generation I plants were early prototypes; Generation IIs were built from the 1960s to the 1990s and include the facility at Fukushima; and Generation IIIs began operating in the late 1990s, though primarily in Japan, France and Russia.)
Unlike their predecessors, most Generation III+ reactors have layers of passive safety elements designed to stave off a meltdown, even in the event of power loss. Construction of the first Generation III+ reactors is well under way in Europe. China is also in the midst of building at least 30 new plants. In the U.S., the Southern Company recently broke ground on the nation’s first Generation III+ reactors at the Vogtle nuclear plant near Augusta, Georgia. The first of two reactors is due to come online in 2016.
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Like many of the 20 or so pending Generation III+ facilities in the U.S., the Vogtle plant will house Westinghouse AP1000 reactors. A light-water reactor, the AP1000 prompts uranium-235 into a chain reaction that throws off high-energy neutrons. The particles heat water into steam, which then turns a turbine that generates electricity.
The greatest danger in a nuclear plant is a meltdown, in which solid reactor fuel overheats, melts, and ruptures its containment shell, releasing radioactive material. (Want more information? Check out our explainer on how nuclear reactors work--and how they fail.) Like most reactors, the AP1000 is cooled with electrically powered water pumps and fans, but it also has a passive safety system, which employs natural forces such as gravity, condensation and evaporation to cool a reactor during a power outage.
A central feature of this system is an 800,000-gallon water tank positioned directly above the containment shell. The reservoir’s valves rely on electrical power to remain closed. When power is lost, the valves open and the water flows down toward the containment shell. Vents passively draw air from outside and direct it over the structure, furthering the evaporative cooling.
Depending on the type of emergency, an additional reservoir within the containment shell can be manually released to flood the reactor. As water boils off, it rises and condenses at the top of the containment shell and streams back down to cool the reactor once more. Unlike today’s plants, most of which have enough backup power onsite to last just four to eight hours after grid power is lost, the AP1000 can safely operate for at least three days without power or human intervention.
Even with their significant safety improvements, Generation III+ plants can, theoretically, melt down. Some people within the nuclear industry are calling for the implementation of still newer reactor designs, collectively called Generation IV. The thorium-powered molten-salt reactor (MSR) is one such design. In an MSR, liquid thorium would replace the solid uranium fuel used in today’s plants, a change that would make meltdowns all but impossiblesingle page
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.