Tomorrow’s options for low-carbon baseload generation.
John A. Bewick is Fortnightly’s contributing editor based in Boston. He formerly was secretary for environmental affairs for the Commonwealth of Massachusetts. He holds advanced degrees in nuclear science and business management.
Harvard Business School Professor Joseph B. Lassiter III puts it bluntly: "The world has allowed nuclear to become virtually an orphaned technology." And that, he adds, despite nuclear's potential to address one of the biggest problems of our time - the need for climate-friendly energy. Lassiter identifies the culprit: "Right now we're letting the ends of the ideological spectrum and the entrenched power of legacy interests stalemate a path to the future." Blocking that path, he notes, are anti-nuclear politics, regulatory policy, and utility investment strategies.
Despite these barriers, however, nuclear power is seeing some resurgence in research and development. Next-generation nuclear technologies are attracting interest from investors with a long lead-time interest in innovative clean energy approaches. The challenge of climate change likely will necessitate a new wave of nuclear plant construction in the next 20 years. Investors naturally want a piece of that.
Over the course of many years, the biggest investors in advanced nuclear technologies have been taxpayers in America and other countries. Governments have funded substantial scientific research and engineering development toward the Generation IV (Gen IV) nuclear reactor. While nuclear plants always have offered power that's virtually free of GHG emissions, along with baseload generation at high availability factors, the new Gen IV concepts offer improvements over current-generation nuclear plants. These include the potential for lower capital costs and electricity prices, abundant fuel, fail-safe operation, dramatic reduction in volume of waste (and a much shorter decay life), and reduced risks of nuclear proliferation.
Lower capital costs for some Gen IV concepts come from improved fuel utilization and lower pressure requirements. Molten salt and sodium-cooled reactors operate at low pressures, and don't require expensive pressure vessels for containment. Where they use molten fuel, they don't require thousands of fuel rods, which are expensive to construct and to replace every four years, when the level of radiation renders them ineffective. The low-cost electricity prices stem from Gen IV technology's use of higher temperature coolants that increase thermal conversion efficiencies to the 45 percent range, where traditional power efficiencies are closer to 33 percent.
Potential fuels include uranium and thorium, but also the vast, inexpensive resources of the tailings from the current uranium enrichment process - and also, importantly, the U.S. inventory of spent nuclear fuel. Fuels are used efficiently, with the consumption of up to 96 percent of the fissionable material in some reactor designs. The broad and diversified sources of fuels mean that these models can supply worldwide power needs for centuries.
Additionally, some Gen IV concepts reduce or eliminate the potential of a hydrogen explosion, such as occurred at Fukushima.These offer fail-safe solutions, without the threat of massive release of radiation.
Gen IV around the World
In the past decade, worldwide adoption of Gen IV concepts to provide power has moved forward deliberately, starting with the creation of an international organization to explore and promote their use.
In January 2000, the U.S. Department of Energy's (DOE) Office of Nuclear Energy, Science and Technology organized a meeting of nations that led to formation of the Generation IV International Forum (GIF).1 The GIF provides a framework for international cooperation in research and development for the next generation nuclear energy systems.2
Among its actions and initiatives, the GIF established goals for Generation IV Nuclear Energy Systems for sustainability, economic impacts, safety and reliability, and proliferation resistance and physical protection, which guided their selection of concepts to be explored. With these goals in mind, GIF had some 100 experts evaluate 130 reactor concepts. This work led to the selection of six reactor technologies for further research and development.3 These include: the gas-cooled fast reactor (GFR), lead-cooled fast reactor (LFR), molten salt reactor (MSR), supercritical water-cooled reactor (SCWR), sodium-cooled fast reactor (SFR), and very high-temperature reactor (VHTR).
After more than a decade, research and development is only beginning to yield results, with several prototypes in active development (none in the United States). In China, for example, construction reportedly is proceeding on "a prototype High Temperature Reactor, HTR-PM," considered a step toward development of the VHTR. Both France and Russia are developing advanced sodium fast-reactor demonstration projects. Russia is planning a prototype lead fast reactor in the 2020 time frame.4 GIF anticipates commercial use of Gen IV technologies in the 2030 to 2040 timeframe.
Why is the innovation in Gen IV not taking place in the U.S. after 50 years of world leadership in nuclear power? The answers are similar to the reasons that the United States also lags behind China in traditional nuclear plant construction investment.5 With the exception of small modular reactor (SMR) technology - toward which U.S. DOE allocated $452 million for development - the United States generally has been moving away from nuclear power for decades.
History is informative. Utilities stopped ordering new nuclear plants in 1978, before the Three Mile Island accident, because capital costs were getting out of control and cost overruns caused some utilities to go bankrupt. In the early 1980s, the OPEC oil embargo was lifted, so the perceived need in the U.S. for nuclear energy diminish. More recently, the low cost of natural gas has destroyed most interest in the nuclear power option among U.S. utilities.
More broadly, policies and market frameworks tend to discourage investments in future technologies in the United States. Regulated utilities are allowed limited budgets for investment in prototype development, and long-term wholesale markets don't support speculative investments in prototypes before commercialization. These shortcomings, coupled with uncertainty of NRC approval of new nuclear reactor designs, currently leave the federal government as the only realistic source of funds for prototype development. Yet DOE has focused mainly on advances in traditional reactor technology, including small modular reactors.
Government-supported investments in solar, wind, biofuels, and other sustainable resources only begin to provide the carbon-free energy required. If the U.S. is to resume its leadership in nuclear technology, it must build prototypes of the advanced nuclear technologies. That would give the nation an opportunity to examine the benefits of the technology, and to carefully review those concepts to ensure that the potential benefits of each are realistic.
Proposed Reactor Projects
Although no Gen IV projects have been sited in the United States, several private-sector opportunities have been proposed, in three of the six GIF categories being investigated. The following concepts are being actively pursued by U.S. companies, both technical developers and venture capitalists. Others are in planning stages, and not yet publicly announced.
- Gas-cooled fast reactor (GFR): A GFR has been proposed by General Atomic (GA) with its Energy Multiplier Module reactor (EM2). GA is reportedly seeking an investor for 75 percent of the project.
- Molten salt reactors (MSR): Several projects with different designs are being proposed, including Transatomic Power (Waste-Annihilating Molten Salt Reactor (WAMSR)), with all seeking funding from public and private sources for testing and prototype development.
- Sodium-cooled fast reactors (SFR): TerraPower, with Bill Gates as a major investor, is seeking a Chinese partner for its first prototype.
The GIF initiative identified a series of factors that distinguish successful Gen IV reactor systems. Namely, they'll provide sustainable energy generation that meets clean air objectives and provides long-term availability of systems and effective fuel utilization for worldwide energy production. They'll minimize and manage their nuclear waste, and notably reduce the long-term stewardship burden, thereby improving protection for the public health and the environment. They'll produce favorable economics, both in terms of life-cycle cost advantages over other energy sources, with financial risks comparable to other energy projects. They'll excel in terms of safety and reliability, with a very low likelihood and degree of reactor core damage, and their designs will eliminate the need for offsite emergency response. Finally, they'll be inherently resistant to proliferation or diversion of materials that could be used as weapons, and they'll provide increased physical protection against acts of terrorism.
Another design, General Atomic's EM2 gas-cooled fast reactor, uses pressurized helium gas as a coolant that operates at high outlet temperatures, about 850 degrees C, using a direct Brayton cycle gas turbine for high thermal efficiency, about 45 percent. It's enclosed in an underground containment structure. With its high temperatures it also can be used to process heat for thermo-chemical production of hydrogen. With its high heat removal rates, it can be much smaller in size (about 25 percent) than conventional nuclear plants, thereby saving on construction costs for the pressure vessel and containment structure.
The fast spectrum also makes it possible to use available fissile and fertile materials (including depleted uranium or low enriched uranium (LEU)) considerably more efficiently than thermal spectrum gas reactors with once-through fuel cycles and a four-year lifetime. The initial fuel load contains about 12 percent enriched uranium. The reactor is designed to be operated for decades without refueling. As a result, it makes greater use of uranium and reduces proliferation risks from easy availability of weapons-grade fuel. The quantity of spent fuel from the fast reactor is lower than that from conventional reactors, since it burns most of the fuel within the long-life core. However it generates large quantities of fissile materials that must be managed and safeguarded. When unusable fission products are removed and stored, the remaining spent fuel can be used to refuel a GFR without conventional reprocessing.
The GFR requires a pressure vessel and components such as new turbines that can withstand the extreme temperatures and pressures. It must have safety systems that allow safe shut-down in the event of an excursion with intrusion of absorber rods and rapid injection of a coolant, since the concept puts high power densities in the core and low thermal inertia with the potential to lead to rapid melting of fuel in an accident. Fuel is placed in silicon carbide cladding to avoid producing hydrogen during an accident.
A thermal pebble bed design was developed in China, starting with the 10 MWt, HTR-10, that reached criticality in 2003 and was tested in 2004 and 2005. China launched construction of twin 250 MWt HTR-PM reactors in 2012, which are expected to begin operation in 2016. This project will have two reactor modules, each of 250 MWt or 105 MWe, using 9 percent enriched fuel (520,000 elements) giving 80 GWd/t discharge burnup. With an outlet temperature of 750 degrees C the pair will drive a single steam cycle turbine at about 40 percent thermal efficiency. This 210 MWe Shidaowan demonstration plant is to pave the way for an 18-unit (3x6, 210-MWe each unit) full-scale power plant on the same site, also using the steam cycle. Plant life is envisaged as 60 years with 85 percent load factor.
Nevertheless, China sees longer-term, fast neutron reactors (FNR) as the main technology, and the China National Nuclear Corp. (CNNC) expects the FNR to become predominant by mid-century. A 65 MWt fast neutron reactor - the Chinese Experimental Fast Reactor (CEFR) - near Beijing achieved criticality in July 2010, and was grid-connected a year later. Based on this, a 600-MWe pre-conceptual design was developed. The current plan is to develop an indigenous 1,000-MWe design to begin construction in 2017, and commissioning in 2023. This is known as the Chinese Demonstration Fast Reactor (CDFR) project 1. It's intended to be followed by a CFR1000 for commercial operation from 2030, according to China Institute of Atomic Energy.6
In the United States, General Atomic (GA) announced its first gas-cooled reactor concept in 1962. In 2009 the company announced its latest concept - the EM2 - with hopes to build a prototype in 2025 with DOE funding needed in the interim to do the basic R&D. The EM2 augments its fissile fuel load with fertile materials to enhance an ultra-long fuel cycle based on a "convert-and-burn" core design, which converts fertile material to fissile fuel and burns it in situ over a 30-year core life without fuel supplementation or shuffling. Currently GA is looking for development partners, possibly DOE funding, and is awaiting an NRC ruling on safety.
The fuel cost of the General Atomic Energy Multiplier Module reactor (EM2) baseline core loading is estimated to be about $200 million, which includes uranium ore, conversion, enrichment, assembly structures, and fabrication costs. This fuel generates 66 TWh of electricity over 30 years at a capacity factor of 95 percent.
The EM2 overnight (without interest charges) capital cost is $3,800 per kWe versus $5,000 to $6,600/kWe for advanced light water plants (ALWR). It would be expected to break even with natural gas combined-cycle plants at a natural gas price of $6 to $7 per MMBtu.
Elsewhere around the world, South Africa announced a pebble bed design in the 2004, which it abandoned in 2010 for lack of funds. Germany built a pebble bed reactor, AVR, (15 MWe) in 1966 and abandoned it in 1988 after the Chernobyl accident led to Germany's reduction in nuclear power.
Japan started an HTTR, FBR, in 1977 that's being upgraded.The Japan Atomic Energy Research Institute built a HTTR 30 MWt, which started up in 1998 and reached 950 degrees C in 2004; and Mitsubishi plans a fast reactor prototype for 2025 with a full power reactor in 2055. GTHTR has been designed up to 600 MWt per module and is being tested. In France, Areva is working with General Atomic with plans for a prototype by 2025.
Finally, for the moment, Europe - through the European Sustainable Nuclear Industrial Initiative - supported development of GCFR with a concept called Allegro, a 100-MWt plant to begin construction in 2018.
Molten Salt Reactor (MSR)
Several new concepts using molten salt as the fuel are under development.
Molten salt reactors use nuclear fuel added to a molten salt such as (LiF-BeF2-ZrF4) or LiF4 heavy metal circulated through a moderator such as graphite or zirconium hydride, to produce a nuclear reaction that heats the molten salt to high temperatures around 800 degrees C. A heat exchanger extracts the heat to make electricity or to produce hydrogen that can be used as a fuel. (At 850 degrees C, it's possible to disassociate hydrogen from water efficiently and produce hydrogen-based fuels.) The high temperatures improve the thermal conversion efficiency to around 45 percent. The salts are already melted, eliminating a core meltdown accident. MSRs have a negative temperature feedback that shuts down the reaction if overheating occurs, and have a fail-safe passive system with a freeze valve at the bottom of the reactor vessel that opens automatically if the salt heats up and drains the fuel to a storage tank with no moderator that shuts down the nuclear reaction automatically.
A molten salt reactor can operate on a large range of fuels, including plutonium and thorium, as well as uranium and nuclear wastes, including spent nuclear fuel and tailings from the uranium enrichment process. The fuel can easily be changed over time. Fuel quantity is minimized because the design eliminates the need for the excess reactivity that must be built into PWR reactors to compensate for the buildup of fission products in fixed fuel rods over time. Finally, fuel can be moved around with a pump.
A solid fuel reactor requires thousands of highly engineered, highly stressed fuel pins. Some fast breeder designs require more than 50,000. Failure of a single fuel pin will shut the reactor down and force a difficult decontamination process. In the molten salt reactor's primary containment there are a few dozen components and only one moving part, a pump, in addition to control rods.
The operating temperature, in the range of 700 to 800 degrees C, translates into thermal efficiencies around 45 percent or higher. By comparison, a PWR reactor operates at about 330 degrees C, with a thermal conversion efficiency of about 33 percent. And a PWR also operates at about 160 bar - a high pressure requiring nine-inch thick reactor vessels and massive piping. A molten salt reactor operates at near ambient pressure. There's no need to pressurize the system since the salts have very high (1,400 degrees C) boiling points at ambient pressure. That eliminates the need for a costly pressure vessel.
The first molten salt reactor was tested at Oak Ridge in the 1960s; it was called the Molten Salt Reactor Experiment (MSRE). Since then there has been some R&D but the program was dropped by the AEC to focus on the liquid metal fast breeder reactor (LMFBR), a program that was cancelled during the Carter administration.
Current international research and development efforts are led by China, where a $350 million MSR program has recently been launched, with a 2-MW test MSR scheduled for completion by around 2020. Smaller MSR research programs are ongoing in France, Russia, and the Czech Republic. Two concepts developed in the U.S. are described below.
Transatomic Power's (TAP) Waste-Annihilating Molten Salt Reactor (WAMSR) can convert the high-level nuclear waste produced by conventional nuclear reactors each year into an estimated $7.1 trillion worth of electricity, or it can use the tailings from the uranium enrichment process as its fuel. At full deployment, TAP's reactors potentially could use existing stockpiles of nuclear waste to satisfy the world's electricity needs through about 2080.
WAMSR can be powered by nuclear waste because it uses radically different technology from conventional plants. Instead of using solid fuel pins, it dissolves the nuclear waste into a molten salt. Suspending the fuel in a liquid allows longer residence in the reactor core, and therefore more capture of its energy. Conventional nuclear reactors can use only about 3 percent of the potential fission energy in a given amount of uranium before it must be removed from the reactor. WAMSR captures 96 percent of this remaining energy. Some of the benefits include:
- Greatly reduced radioactivity: Conventional reactor waste is radioactive for hundreds of thousands of years. The MSR reactor reduces the majority of the fission product waste's radioactive lifetime to hundreds of years, thereby decreasing the need for permanent repositories such as Yucca Mountain.
- Inherently Safe: Unlike conventional reactors, which must rely on operator-activated, external electric power and active safety systems to prevent damage in accident scenarios, the physics of the WAMSR design ensures the reactor is always passively safe. If the molten salt begins to overheat, it triggers a freeze valve at the bottom of the reactor vessel to open and automatically drains the molten salt fuel into storage tanks where the reaction shuts down automatically and can be cooled passively.
- Efficient modular design: The compact 500-MWe molten salt reactor can be manufactured economically at a central location and transported by rail to the reactor site. Utilities can use the profits from the first reactor installed to fund construction of additional units.
- Molten salt reactors are not a new technology: MSRs were originally developed and tested at the Oak Ridge National Laboratory in the 1950s, '60s, and '70s. In many respects, The WAMSR reactor is similar to these early designs. It uses similar safety mechanisms (such as freeze valves), chemical processing techniques (such as off-gas sparging), and corrosion tolerant alloys (such as modified Hastelloy-N).
The main differences between TAP's molten salt reactor and previous molten salt reactors are the zirconium hydride moderator and LiF4 salt. These features allow a more compact reactor unit that generates electricity at lower cost than other designs. Further, previous molten salt reactors, such as the Oak Ridge (MSRE), used uranium enriched to 33 percent U-235. The WAMSR can operate using fresh fuel enriched to a minimum of 1.8 percent U-235, or light water reactor waste.
The WAMSR concept must confirm the adequacy of its innovative design with bench-scale testing of materials and components, such as a fuel salt reprocessing system in an irradiation environment. A prototype then must be built and tested to confirm performance forecasts and to obtain regulatory approvals. Next steps will require raising funds for bench-scale testing and prototype construction.
Sodium-Cooled Fast Reactor (SFR)
The SFR uses liquid sodium as the reactor coolant, allowing high power density with low coolant volume. It builds on the liquid metal fast breeder reactor and the integral fast reactor. The intent is to increase the efficiency of uranium usage by breeding plutonium and eliminating the need for transuranic isotopes ever to leave the site.
The reactor design uses an unmoderated core running on fast neutrons, designed to allow any transuranic isotopes to be consumed, thereby removing the long-life transuranics from the waste cycle. If the fuel overheats, it expands and automatically shuts down the reaction.The fuel is a metallic alloy of uranium and plutonium or spent nuclear fuel contained in a steel cladding. The risks include handling sodium, which is explosive if it comes in contact with water. Use of a metal as the coolant allows the system to work at atmospheric pressure, which reduces the risk of leakage. The advantage of a metallic coolant over water is that water acts as a neutron moderator and reduces the conversion of spent fuel, although water at very high pressure could be used. But that would increase costs, with the need for pressure vessels.
The fast neutron spectrum allows fast reactors to increase the energy yield from natural uranium by a factor of 60 to 70 compared to thermal reactors, opening the potential to realization of nuclear power programs for thousands of years, as well as a significant improvement of nuclear waste management.
The coolant reaches 500 to 550 degrees C and uses a secondary sodium circuit to generate electricity. Some designs require on-site fuel reprocessing. Multiple concepts are being developed. The Terrapower project supported by Bill Gates is described below. There are other projects in China and Europe as well.
The standing wave reactor is a pool-type, sodium-cooled fast reactor. TerraPower (TP) in 2012 advanced to using a standing-wave reactor in order to address the problem of cooling a moving region in a traveling-wave reactor and ineffective use of neutrons. The current design would start the fission reaction at the centre of the reactor core, where the breeding stays, while fresh fuel from the outer edge of the core is progressively moved to the central region, as used fuel is moved out of the centre to the periphery. TP plans to build a 600-MWe demonstration plant by 2022, followed by larger commercial plants of 1,150 MWe in the late 2020s.
TP uses proven technologies for most of the plant with a few notable exceptions. The fuel pins are designed to vent fission product gases to the primary sodium coolant in a controlled manner. Venting the fuel pins enables the deep burnups required to sustain the core for over 40 years and greatly reduces the probability of cladding failures.
TP-1 is similar to other pool-type, sodium-cooled fast reactors in that loss of coolant accidents (LOCA) are eliminated from the design bases. That means that the primary design basis accidents (DBA) are loss of flow (LOF) and loss of heat sink (LOHS). Transient overpower (TOP) events are much less frequent in TP-1 because interlocks prevent excessive rod withdrawal during operations. One difference from previous fast reactor operation is the venting of fission gases from individual fuel pins.
Examples of current sodium-cooled fast reactors include the China Experimental Fast Reactor (CEFR), which was connected to the grid in July 2011, and the BN-800 and Prototype Fast Breeder Reactor (PFBR), under construction in Russia and India, respectively.
In France, the Astrid SFR led by the French CEA involves EdF and Areva and is supported by a French government loan of €651 million. Astrid is based on about 45 reactor-years of operational experience in France and will be rated between 250 and 600 MWe. It's expected to be built at Marcoule beginning in 2017, with commissioning in 2022. Also there's a collective effort in Europe, the 7th European Framework Program's Collaborative Project for a European Sodium Fast Reactor (CP-ESFR).
In Korea, the long-term advanced SFR development plan was authorized by KAEC in 2008 and updated in 2011, which will be carried out toward the construction of an advanced SFR prototype plant by 2028.
In the U.S., the Terrapower project appears to have U.S. government approval for cooperation with China, and TP hopes to build a prototype in China by 2022.
Around the world, government and utility industry initiatives have spurred development of next generation nuclear power plants, both in support of prototype development, and motivated by the urgency of responding to climate change with investment in new generations of carbon-free power plants. Private ventures in the United States have stepped into the next generation nuclear power arena as well, but valuable initiatives here are either stuck, waiting for necessary infusions of private or public investment, or are looking outside the United States for a public development partner.
If U.S. utilities step up to invest in prototype development, or convince the U.S. government to expedite investment in prototype development of Gen IV reactors, energy innovators will be encouraged to keep moving forward with new breakthroughs in technology. Since there's some promise that nuclear waste can be consumed by next generation nuclear reactors, it's likely in the nation's interest to invest, perhaps assigning funds from nuclear waste fees to explore whether Gen IV plants might be the best permanent solution for spent-fuel management - and the future of nuclear power.
2. Original signatories included Argentina, Brazil, Canada, France, Japan, Republic of Korea, South Africa, the United Kingdom and the United States. They have since been joined by Switzerland, Euratom (the European Atomic Energy Community, established by treaty under the European Commission), and, in 2006, by the People's Republic of China and the Russian Federation.
4. See GIF report.
5. China has 28 new nuclear plants in its pipeline, and there are now eight nuclear plants in the U.S. regulatory pipeline. See NRC License applications.