All About Nuclear Energy
nuclear power, is electricity generated by power plants that derive their heat from fission in a nuclear reactor. Except for the reactor, which plays the role of a boiler in a fossil-fuel power plant, a nuclear power plant is similar to a large coal-fired power plant, with pumps, valves, steam generators, turbines, electric generators, condensers, and associated equipment.
World nuclear power
Nuclear power provides almost 15 percent of the world’s electricity. The first nuclear power plants, which were small demonstration facilities, were built in the 1960s. These prototypes provided “proof-of-concept” and laid the groundwork for the development of the higher-power reactors that followed.
The nuclear power industry went through a period of remarkable growth until about 1990, when the portion of electricity generated by nuclear power reached a high of 17 percent. That percentage remained stable through the 1990s and began to decline slowly around the turn of the 21st century, primarily because of the fact that total electricity generation grew faster than electricity from nuclear power while other sources of energy (particularly coal and natural gas) were able to grow more quickly to meet the rising demand. This trend appears likely to continue well into the 21st century. The Energy Information Administration (EIA), a statistical arm of the U.S. Department of Energy, has projected that world electricity generation between 2005 and 2035 will roughly double (from more than 15,000 terawatt-hours to 35,000 terawatt-hours) and that generation from all energy sources except petroleum will continue to grow.
In 2012 more than 400 nuclear reactors were in operation in 30 countries around the world, and more than 60 were under construction. The United States has the largest nuclear power industry, with more than 100 reactors; it is followed by France, which has more than 50. Of the top 15 electricity-producing countries in the world, all but two, Italy and Australia, utilize nuclear power to generate some of their electricity. The overwhelming majority of nuclear reactor generating capacity is concentrated in North America, Europe, and Asia. The early period of the nuclear power industry was dominated by North America (the United States and Canada), but in the 1980s that lead was overtaken by Europe. The EIA projects that Asia will have the largest nuclear capacity by 2035, mainly because of an ambitious building program in China.
A typical nuclear power plant has a generating capacity of approximately one gigawatt (GW; one billion watts) of electricity. At this capacity, a power plant that operates about 90 percent of the time (the U.S. industry average) will generate about eight terawatt-hours of electricity per year. The predominant types of power reactors are pressurized water reactors (PWRs) and boiling water reactors (BWRs), both of which are categorized as light water reactors (LWRs) because they use ordinary (light) water as a moderator and coolant. LWRs make up more than 80 percent of the world’s nuclear reactors, and more than three-quarters of the LWRs are PWRs.
Issues affecting nuclear power
Countries may have a number of motives for deploying nuclear power plants, including a lack of indigenous energy resources, a desire for energy independence, and a goal to limit greenhouse gas emissions by using a carbon-free source of electricity. The benefits of applying nuclear power to these needs are substantial, but they are tempered by a number of issues that need to be considered, including the safety of nuclear reactors, their cost, the disposal of radioactive waste, and a potential for the nuclear fuel cycle to be diverted to the development of nuclear weapons. All of these concerns are discussed below.
Chernobyl NuclearDisaster - 1986
Chernobyl Photo 2 - 1986
Chernobyl Photo3 - 1986
The safety of nuclear reactors has become paramount since the Fukushima accident of 2011. The lessons learned from that disaster included the need to (1) adopt risk-informed regulation, (2) strengthen management systems so that decisions made in the event of a severe accident are based on safety and not cost or political repercussions, (3) periodically assess new information on risks posed by natural hazards such as earthquakes and associated tsunamis, and (4) take steps to mitigate the possible consequences of a station blackout.
The four reactors involved in the Fukushima accident were first-generation BWRs designed in the 1960s. Newer Generation III designs, on the other hand, incorporate improved safety systems and rely more on so-called passive safety designs (i.e., directing cooling water by gravity rather than moving it by pumps) in order to keep the plants safe in the event of a severe accident or station blackout. For instance, in the Westinghouse AP1000 design, residual heat would be removed from the reactor by water circulating under the influence of gravity from reservoirs located inside the reactor’s containment structure. Active and passive safety systems are incorporated into the European Pressurized Water Reactor (EPR) as well.
Traditionally, enhanced safety systems have resulted in higher construction costs, but passive safety designs, by requiring the installation of far fewer pumps, valves, and associated piping, may actually yield a cost saving.
A convenient economic measure used in the power industry is known as the levelized cost of electricity, or LCOE, which is the cost of generating one kilowatt-hour (kWh) of electricity averaged over the lifetime of the power plant. The LCOE is also known as the “busbar cost,” as it represents the cost of the electricity up to the power plant’s busbar, a conducting apparatus that links the plant’s generators and other components to the distribution and transmission equipment that delivers the electricity to the consumer.
The busbar cost of a power plant is determined by 1) capital costs of construction, including finance costs, 2) fuel costs, 3) operation and maintenance (O&M) costs, and 4) decommissioning and waste-disposal costs. For nuclear power plants, busbar costs are dominated by capital costs, which can make up more than 70 percent of the LCOE. Fuel costs, on the other hand, are a relatively small factor in a nuclear plant’s LCOE (less than 20 percent). As a result, the cost of electricity from a nuclear plant is very sensitive to construction costs and interest rates but relatively insensitive to the price of uranium. Indeed, the fuel costs for coal-fired plants tend to be substantially greater than those for nuclear plants. Even though fuel for a nuclear reactor has to be fabricated, the cost of nuclear fuel is substantially less than the cost of fossil fuel per kilowatt-hour of electricity generated. This fuel cost advantage is due to the enormous energy content of each unit of nuclear fuel compared to fossil fuel.
The O&M costs for nuclear plants tend to be higher than those for fossil-fuel plants because of the complexity of a nuclear plant and the regulatory issues that arise during the plant’s operation. Costs for decommissioning and waste disposal are included in fees charged by electrical utilities. In the United States, nuclear-generated electricity was assessed a fee of $0.001 per kilowatt-hour to pay for a permanent repository of high-level nuclear waste. This seemingly modest fee yielded about $750 million per year for the Nuclear Waste Fund.
At the beginning of the 21st century, electricity from nuclear plants typically cost less than electricity from coal-fired plants, but this formula may not apply to the newer generation of nuclear power plants, given the sensitivity of busbar costs to construction costs and interest rates. Another major uncertainty is the possibility of carbon taxes or stricter regulations on carbon dioxide emissions. These measures would almost certainly raise the operating costs of coal plants and thus make nuclear power more competitive.
Spent nuclear reactor fuel and the waste stream generated by fuel reprocessing contain radioactive materials and must be conditioned for permanent disposal. The amount of waste coming out of the nuclear fuel cycle is very small compared with the amount of waste generated by fossil fuel plants. However, nuclear waste is highly radioactive (hence its designation as high-level waste, or HLW), which makes it very dangerous to the public and the environment. Extreme care must be taken to ensure that it is stored safely and securely, preferably deep underground in permanent geologic repositories.
Despite years of research into the science and technology of geologic disposal, no permanent disposal site is in use anywhere in the world. In the last decades of the 20th century, the United States made preparations for constructing a repository for commercial HLW beneath Yucca Mountain, Nevada, but by the turn of the 21st century, this facility had been delayed by legal challenges and political decisions. Pending construction of a long-term repository, U.S. utilities have been storing HLW in so-called dry casks aboveground. Some other countries using nuclear power, such as Finland, Sweden, and France, have made more progress and expect to have HLW repositories operational in the period 2020–25.
The claim has long been made that the development and expansion of commercial nuclear power led to nuclear weapons proliferation, because elements of the nuclear fuel cycle (including uranium enrichment and spent-fuel reprocessing) can also serve as pathways to weapons development. However, the history of nuclear weapons development does not support the notion of a necessary connection between weapons proliferation and commercial nuclear power.
The first pathway to proliferation, uranium enrichment, can lead to a nuclear weapon based on highly enriched uranium (see nuclear weapon: Principles of atomic (fission) weapons). It is considered relatively straightforward for a country to fabricate a weapon with highly enriched uranium, but the impediment historically has been the difficulty of the enrichment process. Since nuclear reactor fuel for LWRs is only slightly enriched (less than 5 percent of the fissile isotope uranium-235) and weapons need a minimum of 20 percent enriched uranium, commercial nuclear power is not a viable pathway to obtaining highly enriched uranium.
The second pathway to proliferation, reprocessing, results in the separation of plutonium from the highly radioactive spent fuel. The plutonium can then be used in a nuclear weapon. However, reprocessing is heavily guarded in those countries where it is conducted, making commercial reprocessing an unlikely pathway for proliferation. Also, it is considered more difficult to construct a weapon with plutonium versus highly enriched uranium.
More than 20 countries have developed nuclear power industries without building nuclear weapons. On the other hand, countries that have built and tested nuclear weapons have followed other paths than purchasing commercial nuclear reactors, reprocessing the spent fuel, and obtaining plutonium. Some have built facilities for the express purpose of enriching uranium; some have built plutonium production reactors; and some have surreptitiously diverted research reactors to the production of plutonium. All these pathways to nuclear proliferation have been more effective, less expensive, and easier to hide from prying eyes than the commercial nuclear power route. Nevertheless, nuclear proliferation remains a highly sensitive issue, and any country that wishes to launch a commercial nuclear power industry will necessarily draw the close attention of oversight bodies such as the International Atomic Energy Agency.
Atomic Energy Commission (United States organization) U.S. federal civilian agency established by the Atomic Energy Act, which was signed into law by President Harry S.
Chernobyl accident (nuclear accident, Union of Soviet Socialist Republics ) Accident in 1986 at the Chernobyl nuclear power station in the Soviet Union, the worst accident in the history of nuclear power generation.
energy conversion (technology) The transformation of energy from forms provided by nature to forms that can be used by humans.
Fukushima accident (Japan ) Accident in 2011 at the Fukushima Daiichi (“Number One”) plant in northern Japan, the second worst nuclear accident in the history of nuclear power generation.
nuclear energy Energy that is released in significant amounts in processes that affect atomic nuclei, the dense cores of atoms.
power (physics) In science and engineering, time rate of doing work or delivering energy, expressible as the amount of work done W, or energy transferred, divided by the time interval t —or W / t.
Safer Nuclear Power, at Half the Price
Transatomic is developing a new kind of molten-salt reactor designed to overcome the major barriers to nuclear power.
Why It Matters
Nuclear energy is a potential source of low-carbon baseload power, but it needs cheaper, safer technology to take off.
Transatomic Power, an MIT spinoff, is developing a nuclear reactor that it estimates will cut the overall cost of a nuclear power plant in half. It’s an updated molten-salt reactor, a type that’s highly resistant to meltdowns. Molten-salt reactors were demonstrated in the 1960s at Oak Ridge National Lab, where one test reactor ran for six years, but the technology hasn’t been used commercially.
The new reactor design, which so far exists only on paper, produces 20 times as much power for its size as Oak Ridge’s technology. That means relatively small, yet powerful, reactors could be built less expensively in factories and shipped by rail instead of being built on site like conventional ones. Transatomic also modified the original molten-salt design to allow it to run on nuclear waste.
High costs, together with concerns about safety and waste disposal, have largely stalled construction of new nuclear plants in the United States and elsewhere (though construction continues in some countries, including China). Japan and Germany even shut down existing plants after the Fukushima accident two years ago (see “Japan’s Economic Troubles Spur a Return to Nuclear” and “Small Nukes Get Boost”). Several companies are trying to address the cost issue by developing small modular reactors that can be built in factories. But these are typically limited to producing 200 megawatts of power, whereas conventional reactors produce more than 1,000 megawatts.
Transatomic says it can split the difference, building a 500-megawatt power plant that achieves some of the cost savings associated with the smaller reactor designs. It estimates that it can build a plant based on such a reactor for $1.7 billion, roughly half the cost per megawatt of current plants. The company has raised $1 million in seed funding, including some from Ray Rothrock, a partner at the VC firm Venrock. Although its cofounders, Mark Massie and Leslie Dewan, are still PhD candidates at MIT, the design has attracted some top advisors, including Regis Matzie, the former CTO of the major nuclear power plant supplier Westinghouse Electric, and Richard Lester, the head of the nuclear engineering department at MIT.
The new reactor is expected to save money not only because it can be built in a factory rather than on site but also because it adds safety features—which could reduce the amount of steel and concrete needed to guard against accidents—and because it runs at atmospheric pressure rather than the high pressures required in conventional reactors.
A conventional nuclear power plant is cooled by water, which boils at a temperature far below the 2,000 °C at the core of a fuel pellet. Even after the reactor is shut down, it must be continuously cooled by pumping in water. The inability to do that is what caused the problems at Fukushima: hydrogen explosions, releases of radiation, and finally meltdown.
Using molten salt as the coolant solves some of these problems. The salt, which is mixed in with the fuel, has a boiling point significantly higher than the temperature of the fuel. The reactor has a built-in thermostat—if it starts to heat up, the salt expands, spreading out the fuel and slowing the reactions. That gives the mixture a chance to cool off. In the event of a power outage, a stopper at the bottom of the reactor melts and the fuel and salt flow into a holding tank, where the fuel spreads out enough for the reactions to stop. The salt then cools and solidifies, encapsulating the radioactive materials. “It’s walk-away safe,” says Dewan, the company’s chief science officer. “If you lose electricity, even if there are no operators on site to pull levers, it will coast to a stop.”
The new design improves on the original molten-salt reactor by changing the internal geometry and using different materials. Transatomic is keeping many of the design details to itself, but one change involves eliminating the graphite that made up 90 percent of the volume of the Oak Ridge reactor. The company has also modified conditions in the reactor to produce faster neutrons, which makes it possible to burn most of the material that is ordinarily discarded as waste. A conventional reactor produces about 20 metric tons of high-level waste a year, and that material needs to be stored for 100,000 years. The 500-megawatt Transatomic reactor will produce only four kilograms of such waste a year, along with 250 kilograms of waste that has to be stored for a few hundred years.
Bringing the new reactor to market will be challenging. Although the basic idea of a molten-salt reactor has been demonstrated, the Nuclear Regulatory Commission’s certification process is set up around light-water reactors. The company will need the NRC to establish new regulations, especially since the commission must sign off on the idea of using less steel and concrete if the design’s safety features are to lead to real savings.
NRC spokesman Scott Burnell says that the commission is aware of Transatomic’s concept but that designs haven’t been submitted for review yet. He says that for the next few years, the NRC will be focused on certifying more conventional designs for small modular reactors. He says the certification process for Transatomic will take at least five years once the company submits a detailed design, with additional review needed specifically for issues related to fuel and waste management.
A detailed engineering design itself may be years away. The company’s next step is raising $5 million to run five experiments to help validate the basic design. Russ Wilcox, Transatomic’s CEO and the former CEO of E Ink, estimates that it will take eight years to build a prototype reactor—at a cost of $200 million. He says that’s less time than it took investors to get a return on E Ink, which was acquired for $450 million 13 years after the first investments in the company.
Even though it could take well over a decade for investors to get a return, venture funding isn’t out of the question, Ray Rothrock says. But he says the company will face many challenges. “The technology doesn’t bother me in the least,” he says. “I have confidence in the people. I wish someone would build this thing, because I think it would work. It’s all the other factors that make it daunting.”
The company’s biggest challenge might come from China, which is investing $350 million over five years to develop molten-salt reactors of its own. It plans to build a two-megawatt test reactor by 2020
CHINA TAKES LEAD ON THORIUM REACTORS
China has officially announced it will launch a program to develop a thorium-fueled molten-salt nuclear reactor, taking a crucial step towards shifting to nuclear power as a primary energy source.
The project was unveiled at the annual Chinese Academy of Sciences conference in Shanghai last week, and reported in the Wen Hui Bao newspaper If the reactor works as planned, China may fulfill a long-delayed dream of clean nuclear energy. The United States could conceivably become dependent on China for next-generation nuclear technology. At the least, the United States could fall dramatically behind in developing green energy.
“President Obama talked about a Sputnik-type call to action in his SOTU address,” wrote Charles Hart, a a retired semiconductor researcher and frequent commenter on the Energy From Thorium discussion forum. “I think this qualifies.”
While nearly all current nuclear reactors run on uranium, the radioactive element thorium is recognized as a safer, cleaner and more abundant alternative fuel. Thorium is particularly well-suited for use in molten-salt reactors, or MSRs. Nuclear reactions take place inside a fluid core rather than solid fuel rods, and there’s no risk of meltdown.
In addition to their safety, MSRs can consume various nuclear-fuel types, including existing stocks of nuclear waste. Their byproducts are unsuitable for making weapons of any type. They can also operate as breeders, producing more fuel than they consume.
In the 1960s and 70s, the United States carried out extensive research on thorium and MSRs at Oak Ridge National Laboratory. That work was abandoned — partly, believe many, because uranium reactors generated bomb-grade plutonium as a byproduct. Today, with nuclear weapons less in demand and cheap oil’s twilight approaching, several countries — including India, France and Norway — are pursuing thorium-based nuclear-fuel cycles.
China’s new program is the largest national thorium-MSR initiative to date. The People’s Republic had already announced plans to build dozens of new nuclear reactors over the next 20 years, increasing its nuclear power supply 20-fold and weaning itself off coal, of which it’s now one of the world’s largest consumers. Designing a thorium-based molten-salt reactor could place China at the forefront of the race to build environmentally safe, cost-effective and politically palatable reactors.
“We need a better stove that can burn more fuel,” Xu Hongjie, a lead researcher at the Shanghai Institute of Applied Physics, told Wen Hui Bao.
China’s program is headed by Jiang Mianheng, son of the former Chinese president Jiang Zemin. A vice president of the Chinese Academy of Sciences, the younger Jiang holds a Ph.D. in electrical engineering from Drexel University. A Chinese delegation headed by Jiang revealed the thorium plans to Oak Ridge scientists during a visit to the national lab last fall.
The official announcement comes as the Obama administration has committed itself to funding R&D for next-generation nuclear technology. The president specifically mentioned Oak Ridge National Laboratory in his State of the Union address Jan. 25, but no government-funded program currently exists to develop thorium as an alternative nuclear fuel.
A Chinese thorium-based nuclear power supply is seen by many nuclear advocates and analysts as a threat to U.S. economic competitiveness. During a presentation at Oak Ridge on Jan. 31, Jim Kennedy, CEO of St. Louis–based Wings Enterprises (which is trying to win approval to start a mine for rare earths and thorium at Pea Ridge, Missouri) portrayed the Chinese thorium development as potentially crippling.
“If we miss the boat on this, how can we possibly compete in the world economy?” Kennedy asked. “What else do we have left to export?”
According to thorium advocates, the United States could find itself 20 years from now importing technology originally developed nearly four decades ago at one of America’s premier national R&D facilities. The alarmist version of China’s next-gen nuclear strategy come down to this: If you like foreign-oil dependency, you’re going to love foreign-nuclear dependency.
“When I heard this, I thought, ‘Oboy, now it’s happened,’” said Kirk Sorensen, chief nuclear technologist at Teledyne Brown Engineering and creator of the Energy From Thorium blog. “Maybe this will get some people’s attention in Washington.”
While the international “Generation IV” nuclear R&D initiative includes a working group on thorium MSRs, China has made clear its intention to go it alone. The Chinese Academy of Sciences announcement explicitly states that the PRC plans to develop and control intellectual property around thorium for its own benefit.
“This will enable China to firmly grasp the lifeline of energy in its own hands,” stated the Wen Hui Bao report.