The nuclear power industry has discussed the potential of fully passive cooling systems for reactors since the first commercial fission plant came on line more than 50 years ago, says Ken Bergeron, a physicist formerly involved with nuclear reactor accident simulations at Sandia National Laboratories in New Mexico. But as yet, a 100% passively cooled reactor is not commercially available, despite advances in adding passive features new nuclear reactors.
The concept behind passively safe nuclear reactors is that they will automatically shut down in an emergency, and reduce the residual heat by cooling the reactor's uranium or plutonium core without the need for human intervention, or the use of electrical power. Instead, a fully passive system would rely on gravity -- rather than valves and pumps -- to naturally circulate coolant around the core to bring its temperature down.
If such a system had been in place in at the Fukushima Dai-ichi plant (pictured), Japan's current nuclear crisis could have been averted, says John McGaha, a board member of the American Nuclear Society.
"The thing that got Japan in trouble was not the earthquake, but the tsunami that took out power supplies [for the water pumps that cooled the reactor cores]," McGaha said. "Passive reactors would have been part of the answer to what happened over there. The passive systems in newer designs don't rely on an outside power source. A passive system happens automatically, even if the operators don't do anything."
Building a Better Nuclear Mousetrap
Several nuclear reactor manufacturers have designed highly advanced passive systems, but they all fall short of being 100% passive because they rely on some externally operated system, such as automatic values to channel the water around the core rather than allowing it to naturally circulate.
Westinghouse Electric has its AP1000 advanced passive system, which is expected to be used in nuclear power plants now under construction in China and the United States. And earlier this month, Westinghouse signed an agreement with Endesa to share its AP1000 technology, with an eye toward selling its system for use in nuclear power plants in Spain and South America.
And French company Areva's EPR next-generation passive reactors are going up in nuclear power projects in India, France and Finland.
"A number of countries around the world are testing and prototyping passive reactors and they're beginning to build them around the world, but I don't know of any that are fully passive and in commercial use now," McGaha said.
One barrier to the widespread adoption of passive reactors has been the cost, Bergeron said, noting that the technology must compete against cheaper power sources such as coal and fossil fuel. But with the world now watching events in Japan unfold, the concept of fully passive nuclear reactors may gain more steam.
"People have talked about passive designs for the past 50 years and since Three Mile Island [nuclear disaster in 1979], interest in [them] has gained," Bergeron said. In his opinion, the situation in Japan will likely spur even more enthusiasm for passive rectors.
Location, Location, Location
While a move to build fully passive nuclear reactors may address some of the problems of a potential meltdown, nipping potential dangers in the bud by being more careful about siting the projects would go a long way, too.
"The wisdom of building near faults will be challenged all over the world, and also building near the ocean where you can have a tsunami," says Bergeron.
The International Atomic Energy Agency says 65 nuclear power plants are under construction around the world, which would add to the 442 nuclear reactors in operation today. And of the reactors in operation, the World Nuclear Association estimates that 20% are located in areas of "significant seismic activity."
Some plants located near seismic fault lines could face a double whammy -- a quake followed tsunami like Japan just suffered -- if they're located near the ocean. In California, the San Onofre nuclear power plant, just a few miles south of the seaside community of San Clemente, sits near the offshore Cristianitos fault line, and would rely on its 30-foot seawall to guard against a tsunami. And along the Central California coast, the Diablo Canyon nuclear power plant is perched on a cliff with a stunning view of the Pacific Ocean -- but it's also close to the San Andreas fault line.
"The proximity to ... the ocean will definitely be taken into consideration [when building a nuclear power plant], like it is today, but more weight will be given to it after Japan," McGaha said. "The plant in Japan withstood a bigger quake than was anticipated, but the force of the tsunami wasn't expected."
A number of older nuclear power plants require a lot of water for their cooling systems -- hence their proximity to coastlines, bays, lakes and rivers, McGaha says. The nuclear industry, however, is gradually replacing water with a more environmentally friendly method for cooling the core: using blasts of air from an air tower. This method avoids dumping heated water back into its source, which can damage fragile aquatic ecosystems.
Locating nuclear power plants further from seismically active areas has its own difficulties, however. Plants are often based as near as is feasible to their customers in order to keep the costs of transmitting the energy from plant to consumer low, Bergeron says. And that often means they get built on the densely populated coasts. But those consumers often have a "not-in-my-backyard" mindset, which pushes plants onto less desirable real estate -- like seismically active zones.
Nuclear Aftershocks Around the World
In the aftermath of the 9.0 earthquake and the ensuing tsunami that ripped through northeastern Japan last week, Taiwan began considering a reduce to its use of nuclear power, Germany put plans to extend the lifespans of its nuclear reactors on hold, and Switzerland put some nuclear power plant approvals on ice, according to a Reuters report.
But in the United States, President Obama reiterated his desire to keep nuclear energy in the mix, as part of his move to diversify America's energy sources away from fossil fuels. Obama's budget proposal includes loan guarantees that would help expand the number of the nation's nuclear power plants. Whether investors will bite is another matter.
After the 1979 incident at Three Mile Island, the nation's worst nuclear disaster, investments in nuclear power went dark for three decades, notes a Bloomberg report.
The impact of Japan's nuclear drama is expected to go beyond international energy policies and investments -- it will very likely force the nuclear industry to re-evaluate how it operates.
"People will look at their plants and see if the standards that they were designed and licensed for are adequate or need to be strengthened," said Victor Gilinsky, a former member of the Nuclear Regulatory Commission. "A lot of the plants were licensed based on earlier earthquake data that is now of questionable validity."