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America's renaissance in nuclear power: Next-generation nuclear reactors strive for radical simplicity
by Mark Williams
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Per Peterson, who joined the Berkeley Engineering faculty in 1990, is an ardent and long-time advocate of nuclear energy. He and his team believe that nuclear power is the least environmentally malign of any of the energy production alternatives.
BART NAGEL PHOTO
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In coming decades, the Earth’s reserve of fossil fuels will be declining just as billions of people in China and India arrive at the First World banquet table, adding new demands to a global energy infrastructure already stressed near its breaking point. All this, as climate change caused by hydrocarbon emissions becomes increasingly evident.
To date, just one energy technology — nuclear energy — has a proven record of coming within shouting distance of solving these problems. France already generates almost 80 percent of its electrical power from nuclear plants, Belgium nearly 60 percent, Sweden 45 percent. The United States generates 20 percent of its electricity from nuclear power plants.
We have more reactors than any other country, according to Berkeley nuclear engineering professor Per Peterson, but we are a very large country, so the need is that much greater. “France closed its last coal mine in 2004. In the United States, 54 percent of our electricity still comes from coal,” says Peterson, an ardent and long-time advocate of nuclear energy.
After the debacle of Three Mile Island’s partial meltdown in 1979, nuclear utilities retrenched and focused solely on improving their ability to reliably run existing plants. During those fallow years, Peterson and a small group of Berkeley-trained engineers, all of whom are passionate environmentalists, played leading roles developing a third-generation reactor design, known as the Economic Simplified Boiling Water Reactor, or the ESBWR. When Peterson joined the Berkeley faculty in 1990, U.S. nuclear plants operated at a 66 percent capacity factor. That number, since then significantly improved, now tops 90 percent.
It would seem that nuclear power’s time has come around again. The ESBWR has been recently chosen for three U.S. sites, while its AP1000 competitor, also designed with simplified safety systems, has been picked for five. While resurgent industry interest in nuclear energy has caught many by surprise, the roots were cultivated over the last 15 years.
“Many of the fundamental modeling and supporting experiments now being used in the licensing process for these new plants were done right here at Berkeley,” says Peterson. “This new generation of plants takes a completely different approach to safety function, incorporating passive safety systems and operating simply by gravity-driven processes. This involves opening just a few valves and eliminates the tangle of safety equipment that needs surveillance, maintenance and protection by security forces.”
Last year, when the ESBWR’s design — owned by General Electric — was selected for development at Grand Gulf in Mississippi, North Anna in Virginia, and River Bend in Louisiana, it was a validation of the work Peterson and his colleagues had accomplished. “It’s very exciting to see how many of the early ideas that we had are bearing fruit today,” says Peterson, who anticipates construction of the new reactors will begin in 2010, once licenses are issued by the Nuclear Regulatory Commission.
Fifty-five years have passed since the debut of the earliest Generation-I nuclear reactors, and now a new generation has arrived. These passive Gen-III+ plants, including the ESBWR, resemble their 1970s-era Gen-II predecessors about as much as a Toyota Prius hybrid resembles a vintage 1972 Pontiac. The arc of technological progress embodied in the Gen-III+ reactors has been a steady move toward radical simplification.
The ESBWR replaces previous reactors’ complex system for residual heat removal with a design that uses no pumps or emergency generators. In fact, this reactor possesses no moving parts at all, except the neutron-absorbing control rods that are pulled partway out from the reactor core to let a controlled fission reaction proceed. That fission reaction generates heat that boils the water in the reactor core. That, in turn, becomes the steam that turns the turbines. When the reactor shuts down, a few valves open, and steam from residual decay heat flows to heat exchangers and condenses, releasing its energy before gravity causes it to flow back down into the core as water. This means that the ESBWR runs entirely on natural circulation forces.
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Rendering shows the reactor core of the Economic Simplified Boiling Water Reactor (ESBWR), which uses no pumps or emergency generators and runs entirely on natural circulation forces. Third-generation reactors like the ESBWR will be fully operational in 2015.
RENDERING COURTESY OF GENERAL ELECTRIC
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“It could not be simpler,” says Atamir Rao, a Berkeley mechanical engineering graduate now posted to Vienna with the International Atomic Energy Agency. “The control rods get pulled out, water comes in and steam goes out, carrying heat that gets turned into electricity.”
Rao has played a vital role bringing the ESBWR to fruition. For almost two decades, as project manager for GE’s nuclear plant division, he pitched the concept and formed alliances wherever he could advance the reactor design’s prospects. “I like nuclear power, in part because I’m a lifetime member of the Sierra Club. Nuclear power is environmentally the least malign of any of the energy production options. And though this doesn’t often get talked about, it’s one of the best options a country can choose. When a nuclear plant is built, the money is spent internally. From a national energy–security viewpoint, too, nuclear is highly attractive.” The countries that will ultimately need nuclear power, Rao continues, are the developing ones like his native India. “Today, I think the biggest challenge for nuclear power is the stranglehold the developed countries have put on it with sanctions.”
In 1990, pushing to advance the EBSWR, Rao brought in Berkeley nuclear engineering professor Virgil Schrock, an expert on reactor thermal hydraulics and safety. “At that time, no market existed for nuclear plants,” Rao recalls. “The price of natural gas was coming down, and nobody thought it would go back up. Simultaneously, utilities companies were finding nuclear plants too expensive and overly complicated. So we looked at simple designs to reduce the scale of the systems.” Though the basic concept for ESBWR existed, Rao and his GE associates then had no solution for the problem of transferring heat in a simple way should there be an accident involving a pipe break. The central difficulty was that non-condensable gases would mix with the steam boiling up from the reactor core, degrading and potentially stopping the whole process of condensation.
It was at this stage that Peterson came on board. “I’d been working on similar problems involving gas-loaded heat pipes,” Peterson says. “So I fit in. Working with Virgil and our graduate students, we solved the basic problem of predicting and controlling the non-condensable gas effects.”
In 1994, Robert Gamble, another Berkeley engineer, joined GE. “While Atam Rao was out raising money, providing vision and running the program, I worked on the technology,” Gamble says. As the twenty-first century came in, he notes, a general recognition seemed to be growing that fossil fuels would be increasingly untenable and nuclear power might be part of the solution. “I think of Atam as carrying the Olympic torch across the United States during the fallow years, then reaching the stadium and handing the torch to me,” Gamble adds with a smile.
Rao credits the testing done at Berkeley as invaluable to the ESBWR’s eventual realization. “But what Per Peterson and Berkeley also did was to realize the design’s value and publish an independent assessment of its economics.” By analyzing how the new reactor’s simplicity and passive systems reduced the quantities of concrete, metal and equipment needed to build the plant, in a 2004 study, Peterson and his Berkeley team showed that the ESBWR could cut a reactor’s capital costs by 25 to 40 percent. “We’d been saying that at GE, but the fact that Berkeley said it gave significant credibility,” Rao says.
“If you can displace coal with less expensive options, then it becomes a different future,” Peterson adds. Nuclear plant costs will become known when utilities request the first bids, but the expectation that these bids will be under $1,500 per kilowatt of capacity places nuclear in direct competition with coal. Moreover, coal-burning plants release enough pollutants to cause 15,000 premature deaths annually in the United States alone. They also contribute substantially to global warming. On the other hand, The ESBWR will release negligible pollutants, except the spent fuel it produces.
So what about that nuclear waste? Peterson believes that the ESBWR is the pinnacle of what can be done with a water-cooled reactor. “It uses completely different construction methods, different design and different safety systems from previous reactors. What’s exactly the same are the materials, the coolant and the fuel cycle.” Changes in those areas, Peterson predicts, are where future improvement lies. The public, he says, will rightfully reject a second repository site beyond the one selected at Yucca Mountain in Nevada. The nuclear industry must work within that limitation, something Peterson considers eminently doable. If nuclear fuel is used more efficiently, he maintains, residual waste could be reduced sufficiently that “the total capacity of a Yucca Mountain could be increased 40 to 100 times."
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All Berkeley engineering alumni, all ardent environmentalists, this team represents a new generation of nuclear engineers engaged in creating a new generation of clean, efficient and economical nuclear reactors. From left: Atamir Rao (Ph.D.’76), Nuclear Power Technology Development Section Head with the International Atomic Energy Agency in Vienna; Robert Gamble (B.S.’86, Ph.D.’02), General Electric Manager, Mechanical Design & Analysis; postdoc Grant Fukuda (Ph.D.’05); and Professor Per Peterson (M.S.’86, Ph.D.’88).
BART NAGEL PHOTO
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The first step to achieving that goal, suggests Peterson, is for the United States to do what most other nuclear nations do: move toward recycling its spent nuclear fuel. “Yucca Mountain would possess the physical capacity to accept spent fuel from all existing reactors and an equal number of new reactors,” Peterson says. “But the development of advanced methods to recycle spent fuel would defer any need to search for a second repository far past the end of this century.” To achieve this long-term goal, Peterson notes, the generation of reactor designs following the ESBWR must be capable of transmuting the heavy elements that accumulate in spent fuel.
Indeed, Peterson points out, because reprocessing likely makes sense in the longer term, there’s no rush to deliver spent fuel to Yucca Mountain. “What makes it challenging to design a waste repository is that the mere placement of the waste creates disturbance,” Peterson explains. “That disturbance chiefly comes from heat as the radioactive elements decay. So we need a guarantee that a place like Yucca Mountain exists where these materials can be safely buried. But it makes no sense to actually bury them there until the materials have had at least 60 years to cool down.”
Meanwhile, the seeds for the ESBWR design were planted in 1990, and the resulting Gen-III+ plants will be built and operating by 2015. Peterson and others around the world who work on advanced reactors have already begun developing models of possible fourth-generation reactors slated for commercial deployment by 2030.
“At some point, we’ll abandon water as a coolant for reactors,” Peterson predicts. Multiple options are now being researched by a small community of experts across the world. Some fourth-generation reactor designs, for instance, would destroy more radioactive waste than they create. Other possibilities include producing hydrogen to power the so-called hydrogen economy, since nuclear reactors can generate high temperatures as well as electricity, which is exactly what it takes to produce hydrogen most efficiently.
Then there are the fifth-generation fusion reactors — the future of the future in nuclear technology, due to arrive around 2050 — where one possible goal is replicating the energy source that powers the sun. That’s no small goal.
“Fusion has the potential to be the cleanest of any of the major power sources,” says Peterson. “In my generation, nobody entered the field of nuclear energy because they thought they’d get rich. We all did it because this is a technology with enormous potential to solve major environmental problems and, moreover, one that we must competently manage because the security implications are so immense.”
Mark Williams is an Oakland-based science writer whose work has appeared in MIT Technology Review, Red Herring and The Economist, among other magazines.
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