MEETING the nation’s—and the world’s—growing demand for electricity is one of the most urgent challenges facing society and the scientific community. Even with improvements in energy efficiency and conservation, a critical need exists to reduce dependence on imported fuels, decrease emissions, and stabilize greenhouse gas concentrations. Safe, environmentally sustainable, commercially attractive sources of baseload electricity are needed with an inherent security of supply and the capacity to meet the level of demand. Renewable sources such as solar, wind, and hydro will play an increasingly important role, but they are not expected to meet the majority of global baseload electricity needs.
The main alternative to burning fossil fuels is nuclear energy. Although attractive on many counts (no carbon emissions, for example), conventional nuclear fission plants face significant challenges such as cost to build; time to license; safety and proliferation issues associated with operations; enrichment; reprocessing; and high-level, long-lived nuclear waste.
The U.S. energy situation becomes particularly acute in the period leading up to the middle part of this century, when the current fleet of nuclear and coal power plants will need to be replaced. “As a national lab, we must respond to the requirement to transform the energy landscape and do so soon enough to make a difference,” says physicist Mike Dunne, Livermore’s program director for Laser Fusion Energy.
The Livermore-led effort to address the need for safe, secure, and sustainable energy is called Laser Inertial Fusion Energy, or LIFE. The development activities are headed by Dunne, with contributions by dozens of Livermore physicists, engineers, and materials scientists, along with major input from many other national laboratories, universities, and industry partners. LIFE draws on the success of the National Ignition Facility (NIF), the world’s largest and most energetic laser system, and the sustained investment in inertial fusion energy by the Department of Energy and its predecessor agencies over the past five decades. Inertial fusion uses powerful lasers to compress and heat the hydrogen isotopes deuterium and tritium to the point of fusion and thereby liberate more energy than was required to ignite the reaction.
On the Brink of Ignition
Deuterium and tritium, the fuels for LIFE, are derived from water and the metal lithium, abundant resources that can provide energy security across the globe. LIFE plants would produce no carbon-based or other harmful emissions. A principal benefit of a LIFE power plant is its intrinsic safety. No possibility would exist of a runaway reaction, a core meltdown, or the release of long-lived radionuclides. Decommissioning would only involve removal of steel and concrete structures for shallow land burial. When operations stop, the residual heat in the system does not require active cooling, so one can just walk away from the plant without any off-site consequences in the event of a natural disaster. The by-product of fusion is helium gas, which avoids the problem of spent-fuel storage.
The heart of LIFE is a laser fusion “engine,” where 2-millimeter-diameter fuel capsules are injected into a chamber about 16 times every second (similar to the rate of an idling car engine). When the nuclei of deuterium and tritium fuse, the reaction creates a helium nucleus and releases a high-energy neutron. The repeated fusion reactions produce a steady stream of neutrons that heat a lithium blanket surrounding the chamber. The heat is used to drive a steam-turbine generator to produce up to 1,500 megawatts of baseload electricity from each plant.
“LIFE economics will be strongly competitive with nuclear power plants and other low-carbon sources of electricity,” says Dunne. The first LIFE power plant is being designed to generate a few hundred megawatts of electricity for the demonstration of continuous operation, high availability, and overall system reliability. Subsequent plants would likely approach a gigawatt or more, benefiting from the significant economies of scale.
LIFE scientist Jeff Latkowski notes that the efficiency of the laser driver in converting energy supplied from the electrical power grid to the energy needed to compress the capsule, coupled with the energy “gain” of the capsule, must be sufficient to yield substantial net energy. The efficiency of the 2.2-megajoule laser driver is calculated to be 16 percent, coupled to a steel-blanket gain of 1.25, a thermoelectric conversion efficiency of 45 percent, and a fusion target gain of 60 (fusion energy divided by laser energy). This combination of efficiencies leads to a commercially acceptable overall plant gain of about 5.
Aiding cost efficiencies is the adoption of modular, line replaceable units (LRUs) throughout the plant. LRUs allow off-site factory construction and easy replacement of individual elements of the system, while maintaining plant operations. The LIFE strategy is to make components small, modular, and cost-effective. Modularity also permits improvements to be made throughout the lifetime of the plant, as long as the new technology fits in the same “box.”
LRUs are used extensively on NIF and were previously instrumental in the atomic vapor laser isotope separation (AVLIS) project at Livermore. AVLIS used high-repetition-rate, multikilowatt lasers to separate isotopes of uranium. For more than 10 years, AVLIS demonstrated 24/7 operation with 99 percent availability. Several current LIFE and NIF managers have had experience running AVLIS. Ed Moses, principal associate director for NIF and Photon Science, for example, directed AVLIS operations for several years.
“Intense design, development, and review have led to enormous progress in the LIFE electrical power plant design over the past two years to meet performance and cost goals,” says Moses. “LIFE will be based on the demonstration of fusion ignition at NIF and will use that facility’s physics platform and architecture. However, the LIFE design has been transformed into a completely modular, factory-built laser system that can be put together and maintained using line replaceable units. An entire LIFE plant will be smaller than NIF and yet produce enough energy to power a city the size of San Francisco.”
Listening to Utilities
LIFE managers regularly confer with electric utility chief executive officers from across the U.S. and abroad. A group of utility executives recently formed an advisory committee to share industry expertise, experience, and insights with the LIFE development team. “When visitors from the power industry tour NIF, they realize a commercial plant could be viable soon enough to make a difference,” says systems engineer Tom Anklam, who heads the effort to integrate LIFE’s many systems.
“We’ve had a staggeringly positive response from the power industry,” says Dunne. “But this is a hard-nosed industry that wants to know how we go from NIF’s proof of principle to operating a commercial fleet of power plants. What matters to utilities is cost to build, cost to operate, reliability, and licensing pathways.”
Engineer Valerie Roberts, deputy principal associate director of NIF and Photon Science Operations, oversaw construction of NIF. Roberts is now working on the project delivery plan. “We want a plant that industry can build easily and reliably,” she says. The LIFE design currently consists of a main fusion operation building, an electrical generation building housing steam turbines, a tritium building for recovering fuel for new fusion targets, a maintenance bay for chamber refurbishment, and all the required support facilities.
An earlier version of LIFE focused on a fusion–fission hybrid design that used waste from nuclear power plants as well as weapons-grade plutonium for fuel. (See S&TR, April/May 2009, Safe and Sustainable Energy with LIFE.) Although this option remains a possibility, the team is now focusing on a pure fusion option.
Instead of enormous cooling towers that characterize many existing power plants, LIFE features advanced forced-air cooling towers just 14 meters tall. Roberts says a LIFE plant could be placed in an urban setting on a site measuring 300,000 to 400,000 square meters (75 to 100 acres). It could also be sited at a retired coal or nuclear power plant to take advantage of much of the existing electrical grid infrastructure.
Fusion Reactions in LIFE Chamber
The chamber is constructed from eight modules that can be withdrawn on rails to a maintenance bay in isolation or as a complete unit. The chamber is housed inside a separate vacuum vessel, with connections only for cooling lines. By decoupling the chamber from the vacuum and optical systems, a relatively rapid exchange can be achieved.
The chamber will be filled with xenon gas to absorb ions and x rays given off by the fusion process, which otherwise would be damaging to the chamber wall materials. The gas does not interfere with the laser beam propagation or target injection.
The ability of a LIFE plant to generate high temperatures (typically 600°C) in the first wall and blanket permits high-efficiency conversion of heat to electricity. Liquid lithium running through both the first wall and blanket will capture the heat. Lithium was chosen as the LIFE coolant because when lithium atoms absorb the neutrons generated by the fusion reactions, the lithium is transmuted to tritium and helium. “A LIFE plant would breed all the tritium needed for the targets,” explains Latkowski. The adjoining tritium plant would take tritium that has been bred in the lithium coolant and unburned tritium from the chamber exhaust gas for use in producing new fusion targets.
A typical LIFE plant will require up to 1.3 million targets daily. Techniques for the manufacture of large quantities of targets are being explored, along with methods to inject them accurately to the center of the target chamber at a velocity of 250 meters per second. A target factory alongside the fusion building will assemble targets from components manufactured off site. Independent analyses of target production factories show that mass production techniques should yield costs of $0.20 to $0.30 per target.
Each LIFE target will contain only about 0.7 milligrams of tritium. The site inventory of tritium will be low, with substantial segregation to ensure safe operations.
Diodes Transform Laser System
Development of high-efficiency, high-repetition-rate, diode-pumped solid-state laser beamlines is under way for several international projects. In addition, technology and experience from Livermore’s AVLIS and Mercury lasers and other high-average-power solid-state lasers is being incorporated into LIFE. Mercury can fire 10 shots a second over extended periods, using cooling technology that is being implemented at a larger scale in the LIFE laser design.
Whereas NIF uses 2-meter-long flashlamps to energize the neodymium atoms in the laser glass amplifiers, LIFE would rely on laser diodes. The diodes are 20 times more efficient than flashlamps, measure 10 to 12 times smaller, and give off substantially less waste heat. “Laser diodes give us the ability to fire 15 times a second, 24 hours, 7 days a week,” says Deri.
More than 100 million diodes will be required for LIFE’s 384 beamlines. “We’re working closely with 14 laser-diode manufacturers to lower costs because diodes will account for a substantial fraction of the laser system’s cost,” says Deri. He compares the team’s association with industry to the cadre of NIF scientists who worked closely with laser glass companies to manufacture affordable laser optics with unprecedented purity and performance.
Deri’s team has designed an entire 1,053-nanometer wavelength infrared-light beamline that fits in one truck-transportable box—a “beamline in a box.” (See the figure below.) Measuring less than 11 meters long, the beamline can be handled as an LRU. The compact size would allow for off-site manufacture, ease of maintenance during operation, and even changeover of individual beamlines while the plant remains operational. Beamlines would also have the ability to enhance their output to compensate for a failed neighboring beam. Optics outside the beam box would convert incoming laser light to 351-nanometer wavelength ultraviolet light for focusing on fusion targets. An important milestone during the intense component development phase will be construction of a “LIFElet,” that is, a full-scale laser beamline for testing.
“We aim to build a demonstration power plant. That’s much different from a typical technology test facility,” says Dunne. “By basing the design on evidence from NIF and using existing technology options, our strategy eliminates the costs and delays associated with a stepwise approach needed for other approaches to fusion. These approaches require multiple facilities to mitigate the risks arising from unproven physics, use of novel materials, and new technologies.”
The team calculates that LIFE plants could deliver 25 percent of U.S. electrical generation by 2050. Estimates of LIFE’s capital and operational costs are highly competitive with other energy alternatives. Rollout of LIFE plants that would displace coal plants beginning in the 2030s could result in a decrease of 90 to 140 billion metric tons of carbon dioxide-equivalent emissions by the end of the century.
While LIFE researchers continue their design work, two national organizations are studying the cost effectiveness and scientific principles behind LIFE. The first study, by the Electric Power Research Institute, focuses on the best avenue toward a working fusion power plant. The second, by the National Research Council, is studying the technology goals, challenges, and path forward for inertial fusion energy.
Dunne believes that a strong national partnership among industry, national laboratories, government, nongovernmental organizations, and academia is required to deliver LIFE. Livermore researchers are already working closely with General Atomics on targets; Savannah River and Los Alamos national laboratories and Princeton Plasma Physics Laboratory on design of tritium systems; the University of Rochester’s Laboratory for Laser Energetics on target and laser designs; the University of Wisconsin, University of California at San Diego, and University of Illinois on target chamber design; the Naval Postgraduate School on welding of specialty steels; and industry on all aspects of the power-generation technology.
“When ignition and gain are achieved on NIF, we will have a substantive delivery plan to take us to a commercial plant,” says Dunne. “We will be ready to go.”
Key Words: deuterium, Electric Power Research Institute, electricity, flashlamp, inertial fusion, laser diode, Laser Inertial Fusion Energy (LIFE), lithium, National Ignition Facility (NIF), National Research Council, nuclear energy, power plant, tritium.
For further information contact Mike Dunne (925) 423-7955 (email@example.com).
Lawrence Livermore National Laboratory
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