The potential for using fusion energy to produce commercial electric power was first explored in the 1960s. Harnessing fusion energy offers the prospect of a nearly-carbon-free energy source with a virtually unlimited supply of fuel (it is derived from deuterium in water). Moreover, unlike nuclear fission plants, fusion power plants, if appropriately designed, would not produce large amounts of high-level nuclear waste requiring long-term disposal. These prospects induced many nations around the world to initiate research and development (R&D) programs aimed at developing fusion as an energy source. Two alternative approaches are being explored: magnetic fusion energy (MFE) and inertial fusion energy (IFE). This report assesses the prospects for IFE, although there are some elements common to the two approaches. Recognizing that the practical realization of fusion energy remains decades away, the committee nonetheless judges that the potential benefits of IFE justify it as part of the long-term U.S. energy R&D portfolio.
To initiate fusion, the deuterium and tritium fuel must be heated to over 50 million degrees and held together long enough for the reactions to take place (see Appendix A). Making inertial fusion a commercial source of energy depends on the ability to implode a fuel target to a high enough temperature and pressure to initiate a fusion reaction that releases on the order of 100 times more energy than was delivered to the target.
The current U.S. fleet of inertial fusion facilities offers a unique opportunity to experiment at “fusion scale,” where fusion conditions are accessible for the first time. Indeed, significant fusion burn is expected on the National Ignition Facility
(NIF) by the end of this decade. A key aim of this study is to determine how best to exploit this opportunity to advance the science and technology of IFE.
CURRENT R&D STATUS
U.S. research on inertial confinement fusion (ICF)—one of the two ways (the other is magnetic confinement fusion) energy is produced by means of fusion— has been supported by the National Nuclear Security Administration (NNSA), primarily for applications related to stewardship of the nuclear-weapons stockpile. This research has benefited inertial fusion for energy applications because the two share many common physics challenges.
The principal research efforts in the United States are aligned along the three major energy sources for driving the implosion of inertial confinement fusion fuel pellets: (1) lasers, including solid state lasers at the Lawrence Livermore National Laboratory’s (LLNL’s) NIF and the University of Rochester’s Laboratory for Laser Energetics (LLE), as well as the krypton fluoride gas lasers at the Naval Research Laboratory; (2) particle beams, being explored by a consortium of laboratories led by the Lawrence Berkeley National Laboratory (LBNL); and (3) pulsed magnetic fields, being explored on the Z machine at Sandia National Laboratories.
There has been substantial scientific and technological progress in inertial confinement fusion during the past decade. Despite these advances, the minimum technical accomplishment that would give confidence that commercial IFE may be feasible—the ignition1 of a fuel pellet in the laboratory—has not been achieved as of this writing.2
For the first time, a research facility, the NIF3 at LLNL, conducted a systematic campaign at an energy scale that was projected to be sufficient to achieve ignition. In anticipation of this, the U.S. Department of Energy (DOE) asked the National Research Council (NRC) to review the prospects for inertial fusion energy with the following statement of task:
- Assess the prospects for generating power using inertial confinement fusion;
- Identify scientific and engineering challenges, cost targets, and R&D objectives associated with developing an IFE demonstration plant; and
- Advise the U.S. Department of Energy on its development of an R&D roadmap aimed at creating a conceptual design for an IFE demonstration plant.
1 In this report, ignition is defined as “scientific breakeven,” in which the target releases an amount of energy equal to the energy incident upon it to drive the implosion.
2 As of December 27, 2012.
3 The NIF, which was designed for stockpile stewardship applications, currently uses a solid-state laser driver and an indirect-drive target configuration.
A comparison of inertial fusion energy to magnetic fusion energy or any other potential or available energy technologies, such as wind or nuclear fission, while it would be a very interesting subject of study, was outside the committee’s purview.
The National Ignition Campaign being carried out at the NIF has made significant technical progress during the past year. Nevertheless, ignition has taken longer than scheduled. The results of the experiments performed to date have differed from model projections and are not yet fully understood. It will likely take much more than a year from now to gain a full understanding of the discrepancies between theory and experiment and to make needed modifications to optimize target performance.4 Box 1.1 in Chapter 1, “Recent Results from the National Ignition Facility,” provides a detailed discussion of the most recent NIF results, and Appendix I provides a more technical discussion of this subject.
While the committee considers the achievement of ignition as an essential prerequisite for initiating a national, coordinated, broad-based inertial fusion energy program, it does not believe that the fact that NIF did not achieve ignition by the end of the National Ignition Campaign (September 30, 2012) lessens the long-term technical prospects for IFE. It is important to note that none of the expert committees5 that reviewed NIF’s target performance concluded that ignition would not be achievable at the facility. Furthermore, as the Panel on the Assessment of ICF Target concluded, “So far as target physics is concerned, it is a modest step from NIF scale to IFE scale.”6 A better understanding of the physics of indirect-drive implosions is needed, as well as improved capabilities for simulating them. In addition, alternative implosion modes (laser direct drive, shock ignition, heavy-ion drive, and pulsed-power drive) have yet to be adequately explored. It will therefore be critical that the unique capabilities of the NIF be used to determine the viability of ignition at the million joule energy scale.
As the scientific basis for IFE is better understood—e.g., ignition is achieved or the conditions for ignition are better understood—the path forward for IFE research will diverge from that for NNSA’s weapons research program because technologies specific to IFE (e.g., high-repetition-rate driver modules, chamber materials, mass-producible targets) will need to receive a higher priority.
4 NNSA, 2012. NNSA’s Path Forward to Achieving Ignition in the Inertial Confinement Fusion Program: Report to Congress, December.
5 DOE Memo by D.H. Crandall to D.L. Cook, “External Review of the National Ignition Campaign,” July 19, 2012; National Ignition Campaign Technical Review Committee, “The National Ignition Campaign Technical Review Committee Report, for the Meeting Held on May 30 through June 1, 2012”; NRC, 2013, Assessment of Inertial Confinement Fusion Targets, Washington, D.C.: The National Academies Press.
6 See Overarching Conclusion 1 from Assessment of Inertial Confinement Fusion Targets, 2013.
PRINCIPAL CONCLUSIONS AND RECOMMENDATIONS
With substantial input from the community, the committee conducted an intensive review of approaches to IFE—diode-pumped lasers, krypton fluoride lasers, heavy-ion accelerators, pulsed power, as well as indirect drive7 and direct drive.8 The committee’s principal conclusions and recommendations regarding its assessment of the prospects for IFE are given below. They are grouped thematically under several general topic headings. Additional conclusions and recommendations are contained in the individual chapters. Where there is overlap, the conclusions and recommendations are numbered as they appear in the chapters, to point the reader to the location of more detailed discussion. The recommendations are made in view of the current technical uncertainties and the anticipated long time frame to achieve commercialization of IFE.
Potential Benefits, Recent Progress, and Current Status of Inertial Fusion Energy
Conclusion: The scientific and technological progress in inertial confinement fusion has been substantial during the past decade, particularly in areas pertaining to the achievement and understanding of high-energy-density conditions in the compressed fuel, and in exploring several of the critical technologies required for inertial fusion energy applications—high-repetition-rate lasers and heavy-ion-beam systems, pulsed-power systems, and cryogenic target fabrication techniques. (Conclusion 1 from the Interim Report;9 Chapters 2 and 3 of this report)
Conclusion: It would be premature to choose a particular driver approach as the preferred option for an inertial fusion energy demonstration plant at the present time. (Conclusion 2 from the Interim Report)
Conclusion: The potential benefits of energy from inertial confinement fusion (abundant fuel, minimal greenhouse gas emissions, and limited high-level radioactive waste requiring long-term disposal) also provide a compelling rationale for including inertial fusion energy R&D as part of the long-term
7 In an indirect-drive target, the driver energy strikes the inner surface of a hollow chamber (the “hohlraum”) that surrounds the fuel capsule, exciting X-rays that transfer energy to the capsule.
8 In a direct-drive target, the driver energy strikes directly on the fuel capsule. The illumination geometry of the driver beams may be oblique—i.e., from diametrically opposite sides, called “polar direct drive”—or spherically symmetric.
9 NRC, 2012. Interim Report—Status of the Study “Assessment of the Prospects for Inertial Fusion Energy,” Washington, D.C.: The National Academies Press.
R&D portfolio for U.S. energy. A portfolio strategy hedges against uncertainties in the future availability of alternatives such as those that arise from unforeseen circumstances. (Conclusion 1-1)
Factors Influencing the Commercialization of Inertial Fusion Energy
Conclusion: The cost of targets has a major impact on the economics of inertial fusion energy power plants. Very large extrapolations are required from the current state of the art for fabricating targets for inertial confinement fusion research to the ability to mass-produce inexpensive targets for inertial fusion energy systems. (Conclusion 3-24)
Conclusion: As presently understood, an inertial fusion energy power plant would have a high capital cost and would therefore have to operate with a high availability. Achieving high availabilities is a major challenge for fusion energy systems. It would involve substantial testing of IFE plant components and the development of sophisticated remote maintenance approaches. (Conclusion 3-23)
Recommendation: Economic analyses of inertial fusion energy power systems should be an integral part of national program planning efforts, particularly as more cost data become available. (Recommendation 3-10)
Recommendation: A comprehensive systems engineering approach should be used to assess the performance of IFE systems. Such analysis should use a Technology Readiness Level (TRL) methodology to help guide the allocation of R&D funds. (Recommendation 3-11)
Conclusion: Some licensing/regulatory-related research has been carried out for the ITER (magnetic fusion energy) program, and much of that work provides insights into the licensing process and issues for inertial fusion energy. The Laser Inertial Fusion Energy (LIFE) program at Lawrence Livermore National Laboratory has considered licensing issues more than any other IFE approach; however, much more effort would be required when a Nuclear Regulatory Commission license is pursued for inertial fusion energy. (Conclusion 3-20)
The Establishment of an Integrated National Inertial Fusion Energy Program and Its Characteristics
Conclusion: While there have been diverse past and ongoing research efforts sponsored by various agencies and funding mechanisms that are relevant to IFE, at the present time there is no nationally coordinated R&D program in the United States aimed at the development of inertial fusion energy that incorporates the spectrum of driver approaches (diode-pumped lasers, heavy ions, krypton fluoride lasers, pulsed power, or other concepts), the spectrum of target designs, or any of the unique technologies needed to extract energy from any of the variety of driver and target options. (Conclusion 4-9)
Conclusion: Funding for inertial confinement fusion is largely motivated by the U.S. nuclear weapons program, because of its relevance to stewardship of the nuclear stockpile. The National Nuclear Security Administration (NNSA) does not have an energy mission and—in the event that ignition is achieved—the NNSA and inertial fusion energy research efforts will continue to diverge as technologies relevant to IFE (e.g., high-repetition-rate driver modules, chamber materials, and mass-producible targets) begin to receive a higher priority in the IFE program. (Conclusion 4-10)
Conclusion: The appropriate time for the establishment of a national, coordinated, broad-based inertial fusion energy program within DOE would be when ignition is achieved. (Conclusion 4-13)
Conclusion: At the present time, there is no single administrative home within the Department of Energy that has been invested with the responsibility for administering a national inertial fusion energy R&D program. (Conclusion 4-16)
Recommendation: In the event that ignition is achieved on the National Ignition Facility or another facility, and assuming that there is a federal commitment to establish a national inertial fusion energy R&D program, the Department of Energy should develop plans to administer such a national program (including both science and technology research) through a single program office. (Recommendation 4-11)
Recommendation: The Department of Energy should use a milestone-based roadmap approach based on technology readiness levels (TRLs) to assist in planning the recommended national IFE program leading to a demonstration plant. The plans should be updated regularly to reassess each potential approach and set priorities based on the level of progress. Suitable milestones
for each driver-target pair considered might include, at a minimum, the following technical goals:
- Reproducible modest gain,
- Reactor-scale gain,
- Reactor-scale gain with a cost-effective target, and
- Reactor-scale gain with the required repetition rate. (Recommendation 4-4)
Recommendation: The national inertial fusion energy technology effort should leverage materials and technology development from magnetic fusion energy efforts in the United States and abroad. Examples include ITER’s test blanket module R&D program, materials development, plasma-facing components, tritium fuel cycle, remote handling, and fusion safety analysis tools. (Recommendation 3-2)
Inertial Fusion Energy Drivers
Conclusion: Each target design and each driver approach has potential advantages and uncertainties to the extent that “the best driver approach” remains an open question. (Conclusion 4-5)
Conclusion: If the diode-pumped, solid-state laser technical approach is selected for the roadmap development path, the demonstration of a diode-pumped, solid-state laser beam-line module and line-replaceable unit at full scale would be a critical step in the development of a laser driver for IFE. (Conclusion 2-2)
Conclusion: If the KrF laser technical approach is selected for the roadmap development path, a very important element of the KrF laser inertial fusion energy research and development program would be the demonstration of a multikilojoule 5- to 10-Hz KrF laser module that meets all of the requirements for a Fusion Test Facility. (Conclusion 2-6)
Conclusion: Demonstrating that the Neutralized Drift Compression Experiment-II (NDCX-II) meets its energy, current, pulse length, and spot-size
objectives is of great technical importance, both for heavy-ion inertial fusion energy applications and for high-energy-density physics. (Conclusion 2-7)
Conclusion: Restarting the High-Current Experiment to undertake driver-scale beam transport experiments and restarting the enabling technology programs are crucial to reestablishing a heavy-ion fusion program. (Conclusion 2-8)
Conclusion: There has been considerable progress in the development of efficient pulsed-power drivers of the type needed for inertial confinement fusion applications, and the funding is in place to continue along that path. (Conclusion 2-12)
Conclusion: The major technology development issues that would have to be resolved to make a pulsed-power IFE system feasible—the recyclable transmission line and the ultra-high-yield chamber—are not receiving any significant attention. (Conclusion 2-14)
Recommendation: Physics issues associated with the Magnetized Liner Inertial Fusion (MagLIF) concept should be addressed in single-pulse mode during the next 5 years so as to determine its scientific feasibility. (Recommendation 2-2)
Recommendation: Technical issues associated with the viability of recyclable transmission lines and 0.1-Hz, 10-GJ-yield chambers should be addressed with engineering feasibility studies in the next 5 years to assess the technical feasibility of MagLIF as an inertial fusion energy system option. (Recommendation 2-3)
Other Critical Technologies for Inertial Fusion Energy
Conclusion: Significant IFE technology research and engineering efforts are required to identify and develop solutions for critical technology issues and systems, among them targets and target systems; reaction chambers (first wall/blanket/shield); materials development; tritium production, recovery, and management systems; environment and safety protection systems; and economic analysis. (Conclusion 3-3)
Conclusion: An inertial fusion energy program would require expanded effort on target fabrication, injection, tracking, survivability, and recycling. Target technologies developed in the laboratory would need to be demonstrated on industrial mass production equipment. A target technology program would be required for all promising inertial fusion energy options, consistent with budgetary constraints. (Conclusion 3-9)
Conclusion: The chamber and blanket are critical elements of an inertial fusion energy power plant, providing the means to convert the energy released in fusion reactions into useful applications as well as the means to breed the tritium fuel. The choice and design of chamber technologies are strongly coupled to the choice and design of driver and target technologies. A coordinated development program is needed. (Conclusion 3-10)
The National Ignition Facility
Conclusion: The National Ignition Facility, designed for stockpile stewardship applications, is also of great potential importance for advancing the technical basis for inertial fusion energy research. (Conclusion 4-15)
Conclusion: There has been good technical progress during the past year in the ignition campaign carried out on the National Ignition Facility. Nevertheless, ignition has been more difficult than anticipated and was not achieved in the National Ignition Campaign, which ended on September 30, 2012. The results of experiments to date are not fully understood. It will likely take significantly more than a year to gain a full understanding of the discrepancies between theory and experiment and to make modifications needed to optimize target performance. (Conclusion 2-1)
Recommendation: The target physics programs on the NIF, Nike, OMEGA, and Z should receive continued high priority. The program on NIF should be expanded to include direct drive and alternative modes of ignition. It should aim for ignition with moderate gain and comprehensive scientific understanding, leading to codes with predictive capabilities for a broad range of IFE targets. (Recommendation 2-1)
Recommendation: The achievement of ignition with laser-indirect drive at the National Ignition Facility should not preclude experiments to test the feasibility of laser-direct drive. Direct-drive experiments should also be carried out because of their potential for achieving higher gain and/or other technological advantages. (Recommendation 4-7)
Recommendation: Planning should begin for making effective use of the National Ignition Facility as one of the major program elements in an assessment of the feasibility of inertial fusion energy. (Recommendation from the Interim Report and Recommendation 4-10 from this report)
The NRC Panel on the Assessment of Inertial Confinement Fusion Targets has examined the proliferation risks associated with IFE systems. Its analysis and principal conclusions regarding proliferation risks are presented in Chapter 3 of its report, Assessment of Inertial Confinement Fusion Targets. The NRC Committee on the Prospects for Inertial Confinement Fusion Energy Systems concurs with the Panel’s conclusions, which are reiterated below for completeness.
Conclusion: At present, there are more proliferation concerns associated with indirect-drive targets than with direct-drive targets. However, worldwide technology developments may eventually render these concerns moot.10 Remaining concerns are likely to focus on the use of classified codes for target design. (Conclusion 3-1 from the panel report)
Conclusion: The nuclear weapons proliferation risks associated with fusion power plants are real, but are likely to be controllable.11 These risks fall into three categories: knowledge transfer; Special Nuclear Material (SNM) production; and tritium diversion. (Conclusion 3-2 from the panel report)
Conclusion: Research facilities are likely to be a greater proliferation concern than power plants. A working power plant is less flexible than a research facility, and it is likely to be more difficult to explore a range of physics problems with a power plant. However, domestic research facilities (which may have a
10 Progress in experiment and computation may eventually result in data, simulations, and knowl edge that the U.S. presently considers classified becoming widely available. Classification concerns about different kinds of targets may then change considerably.
11 Proliferation of knowledge and production of Special Nuclear Material are subject to control by international inspection of research facilities and plants; tritium diversion is a problem that will require careful attention.
mix of defense and scientific missions) are more complicated to put under international safeguards than commercial power plants. Furthermore, the issue of proliferation from research facilities will have to be dealt with long before proliferation from potential power plants becomes a concern. (Conclusion 3-3 from the panel report)
Conclusion: It will be important to consider international engagement regarding the potential for proliferation associated with IFE power plants. (Conclusion 3-4 from the panel report)