Feasibility of Inertial-Confinement Fusion

Home , John Nuckolls, Novette laser, Shiva laser

On October 15, 1981, John H. Nuckolls this article has occurred because of the received the American Physical Society's dedication and inspiration of John Maxwell Prize for outstanding contribu Nuckolls and his colleagues at LLNL, as tions to plasma physics. The citation read well as of hundreds of researchers else "For his contributions to the genesis and where in the United States and other na progress of inertial confinement fusion. tions. In addition to their work, consistent His insight into the fundamental physics support for the U.S. Inertial Fusion Pro issues has served to guide and inspire the gram has been provided by the Depart technical evolution of the field." An article ment of Energy and its predecessors and based on his Maxwell lecture to the Soci by the Congress of the United States. This ety was published in Physics Today (Sep support has led, in 10 years time, to an ef tember 1982). Because of the interest that fort with the accomplishments and scope readers of the En ergy and Technol ogy described in this article. It should be fur Review could have in John's views on ther noted that, although the thrust of this John's views on inertial confinement fusion, the editors article is directed toward the long-range power-potential of the En ergy and Technology Review have agreed to re of the Inertial Fusion Program, current support and print the article in this issue. The work described in nearer-term goals are defense related. Feasibility of Inertial Confinement Fusion "We can see no insurmountable roadblocks to th e practi temperatures sufficient to cause the hy cal achievement of electrical power generated by in ertial drogen nuclei to fuse, releasing an confinement fusion ... An ICF reactor may have a rela amount of energy equivalent to that of tively small containment volume [and] its operation, a barrel of oil (see Physics Today, maintenance, and repair will be relatively simple." August 1973, page 46). Those who are skeptical of the inertial-confinement fusion program For further information contact So concluded the chairman of a have a number of objections. They cite John Nuckolls (415) 422-5435. Department of Energy ad hoc commit the fact that the magnetic-fusion tee of experts in 1979, after a compre machines-tokamaks and mirrors-are Reprinted, with permission, from Physics Today, hensive review of the U.S. inertial several years ahead, and they note the 1 September 1982. confinement fusion program. In spite time and effort that will be required to of this positive evaluation, the role of solve the technical problems, princi inertial-confinement fusion in the total pally the coupling of the laser beam to . U.s. energy program continues to be a the target, the confinement of the subject of disagreement.2 Before I men fusion explosion, and the development tion the issues of contention, let me de of a practical driver. scribe inertial-confinement fusion During the past three years, how briefly. In a typical reactor scheme, a ever, inertial-confinement fusion has pea-sized target pellet containing hy made substantial progress toward solv drogen isotopes is projected into a reac ing its principal scientific and techno tor chamber, where it is suddenly ir logical problems. The program has: radiated with an intense beam of light • Achieved efficient beam-target or ions from a "driver" (Fig. 1). As the coupling using short-wavelength lasers, surface of the target blasts away, the • Achieved high-density implosions rocket-like reaction forces implode the with so-called "hohlraum" targets, target's interior to densities and which we will discuss later,

18 DEFENSE PROGRAMS

• Improved the design of damage In 1980, Congress and the President proof fluid walls for reactors with high strongly endorsed accelerated develop power densities, ment of magnetic fusion. Although eco • Designed drivers of higher effi nomic difficulties in the United States ciency and lower cost, and have postponed this growth, the ur • Planned to utilize the physical gency for fusion continues to increase. separation of the reactor and the high The Middle East, source of much of our technology components-the driver oil, is unstable. Weaknesses and uncer and the target factory-which several tainties are emerging in the coal-fission reactors can share. These developments strategy for energy independence. Fis make possible fusion reactors with sion energy is increasingly impeded by minimum cost and radioactive waste. Murphy's Law (what can go wrong, will) and growing public opposition, The Rise of Fusion while coal energy is generating acid In 1942, Hans Bethe, Enrico Fermi, rain and in the 21st century may pro Fig. 1 J. Robert Oppenheimer, Edward Teller, duce major global climate changes Inertial-confinement-fusion reactor and others began to develop the phys through the CO2 greenhouse effect. concept known as HYLIFE. A shower ics of practical fusion. Later, at Los To contribute to the solution of these of liquid lithium shields the first wall Alamos, fusion research was driven by energy problems in the next century, from damaging neutrons, x rays, and the determination and technical leader inertial fusion must meet several diffi hot plasma from exploding fuel pel ship of Teller. In 1952, seven years after cult challenges. The DOE experts' com lets. With an average lithium thickness of 50 cm, the neutron damage is suffi development of the atomic trigger, seis mittee, which was headed by John ciently reduced to increase the life mographs worldwide registered the Foster, Jr., vice-president of science and time of the first wall tenfold. The success of the multimegaton inertial technology at TRW Inc., and former neutron-induced radioactivity in the confinement device. In the 1950s, the DOD Director of Defense Research and reactor structure is reduced 10- to extraordinary promise of controlled Engineering and Director of Lawrence 100-fold. The average power at the first wall is relatively high, approxi fusion-safe, clean, low-cost energy Livermore, noted that " .. . many prob mately 10 MW/ m2. More than 90% of with inexhaustible fuel accessible to all lems and unknowns remain, but this power is absorbed by the liquid nations-led to research programs on because of the wealth of promising lithium. magnetic-confinement fusion at many scientific laboratories. The 1960s saw ~GraPhite plug the conception and calculation of iner ~!I!F . tial approaches to controlled fusion, in cluding schemes based on implosions driven by laser and charged-particle beams. The energy crisis stimulated rapid .,...----Laser or heavy growth in both the magnetic and ion beams inertial-confinement fusion programs in the early 1970s. The inertial confinement fusion programs at LLNL, the University of Rochester Laboratory for Laser Energies, the Lebedev Insti tute in the USSR, and Limeil Labora tories in France were joined by the new programs at KMS Fusion Inc., Los Liquid-metal jet array Alamos and Sandia National Labora Coolant channels Beam and pellet tories, Naval Research Laboratory, Rutherford Laboratory in England, Graphite reflector Osaka University in Japan, Max Planck Institute at Garching in West Germany, and laboratories elsewhere. Rapid growth was sustained throughout the 1970s, driven by OPEC policies, fis Laser or----- sion's political and technical difficulties, heavy-ion beams and fusion's scientific progress.

19 approaches, it seems plausible that with The hohlraum target designs are a continued national effort, a prototype classified. experimental IeF reactor will be in op Inertial-confinement fusion must eration by the turn of the century."l demonstrate that one can achieve a suf What are these problems, unknowns, ficiently high target gain with an af and promising approaches? fordable driver. Target gain is the ratio As we have indicated above, the key of the energy yield of the fusion reac idea of inertial-confinement fusion is to tion to the driver energy applied to the ignite small-scale, contained fusion ex target. Assuming driver and implosion plosions by using high-power beams of efficiencies of 10%, the target gain must energy that implode fuel to superhigh be greater than 100. Such a gain is fea densities and thermonuclear tempera sible with multimegajoule drivers if tures. For both inertial and magnetic three conditions are satisfied: the beam fusion, burn efficiency-the percentage couples efficiently to the target, the fuel of nuclei that fuse-is proportional to is efficiently compressed to 1000 times the product of density and confinement its liquid density, and a small fraction time. In magnetic fusion, the fuel den of the fuel is ignited at the center of the sity is limited by material properties, so target pellet. The remaining fuel must one increases the efficiency of the burn also ignite by propagation from the by extending the duration of confine central ignited region and burn ment. In inertial fusion, Newton's laws efficien tl y. and thermal velocity limit the confine For practical fusion power, we must ment time, so one tries to compress the develop three technologies to harness fuel to higher densities. Densities up to the high-gain targets: an efficient and 1000 g/cm3 are energetically accessible affordable driver that couples efficiently via isentropic, or constant-entropy, to the target, a practical and economi compression because the Fermi cally competitive reactor that incorpo energy-the minimum energy of com rates solutions to the problems of cyclic pressed matter- is much less than the fatigue and stress from pulsed radia thermal energy at ignition. tion, and a practical target factory. We There are two basic target designs will address these scientific and techno for inertial-confinement fusion reactors: logical issues . • Direct targets absorb the driver By using high-intensity short Fig. 2 beam energy in an outer layer or wavelength laser light, researchers have Absorption of laser light by targets in "shell," which acts directly to produce improved the absorption of energy by c reases d r amat ically with shorter the implosion. targets and reduced the production of wavelengths. From bottom t o t op, • Hohlraum targets absorb the hot electrons, which heat the interior of curves cover data points from experi ments at 1, 1/ 2, an d 1/ 3 mic ron. driver energy and convert it to x rays, the fuel pellet and make compression (Data from Ecole Poly technique, Uni which are contained by a radiation case less efficient. Figure 2 shows the results versity of Rochester, and LLN L.) and are used to drive the implosion. of laser-plasma coupling experiments in which absorption was measured3 as a 100 r------~------,_------__, function of intensity for three laser . , • • I wavelengths: 1, 1/2, and 1/3 micron. 80 • I Inertial-confinement fusion targets are 14 • I designed to operate at intensities of 10 15 2 oR. . 0 1 to 10 W/cm At these intensities, C 60 • there is 90% absorption of short .!:! I C. • wavelength light. Also, fewer hot elec 0 •• 1 III 40 trons are produced with shorter laser ..c 3

20 DEFENSE PROGRAMS confirms our theoretical predictions.5 1014 Collisional absorption (inverse brems • strahlung) competes with collective ab I- • Gold disks sorption-principally by way of 2 Brillouin and Raman scattering, self • I ~ 300 TW/ cm 1012 l-• T ~ 600 ps focusing or "filamentation," and the I< ~ v two-plasmon decay instability. At :> • 41 shorter wavelengths, laser light pene .:.: l- ••• >"- trates into denser plasma with higher 41 .:.: • • collision frequency. This raises the a) 1010 f- •• 0 threshold for collective instabilities. c:: • 41 ~ Current experiments involve plasmas :;:: I- of millimeter scale length. We must >- • • ~ also carry out plasma experiments to X • test our theoretical predictions at the lOB f- • centimeter scale lengths characteristic • of reactor targets. In addition, we need - space- and time-resolved measurements of the plasma density profiles and tem I I I I I I I 106 peratures to confirm our understanding 0 10 20 30 40 50 60 70 80 of the details of the laser-plasma Energy, keV interaction. parameter (the product of density and Fig. 3 Scientific Feasibility confinement time) greater than Superthermal x rays decrease by over 14 The highest density achieved to date 10 cm - 3 . s. The Nova I experiments two orders of magnitude when in laser implosion experiments with should reach the threshold of igni shorter-wavelength laser light is used. 14 deuterium-tritium fuel is 100 times that tion-that is, nt > 3 X 10 cm - 3 . sand Such x rays indicate the presence of of the liquid. As Fig. 4 shows, this temperatures of about 2 keY. Because superthermal electrons capable of heating the target prematurely. The superdense material had a temperature of the inefficiencies of the driver and three x-ray energy spectra shown of half a keY and a pressure of 1010 the implosion, inertial-confinement here are from experiments on gold atmospheres. These results are in good fusion has to push nt a factor of 10 fur disk targets exposed to laser light fo 14 2 agreement with theory and with de ther than magnetic fusion to reach con cused to about 3 X 10 W/ cm • From tailed calculations using a complex ditions that could lead to practical top to bottom, curves cover data points from experiments at 1, 1/ 2, magnetohydrodynamics-fusion com reactors. and 1 / 3 micron. puter program called LASNEX. To The next major challenge for inertial ignite reactor-scale targets, the confinement fusion is to demonstrate deuterium-tritium must be imploded to scientific feasibility. Before a reactor a thousand times liquid density and 1000 ,...------.... multi-keY temperatures. The ignition PBFA-II pressure is about 1012 atmospheres. We NOVA I expect to achieve 200 to 400 times LLNL liquid density with the lO-k], 11 100 flol LLNL 1/3-micron Novette laser by 1984-85, 10 ~ 'iii LLNL ~bl and 1000 times liquid density with the c:: T ~o -l 41 III KMS 100-kJ, 1/3-micron Nova I laser by 1:l 1 Fig. 4 1:l USSR 161 "- 1986-88. ':; LASL 1,- 1 LLNL Results of experiments at various In these high-density Nova experi _g 10 i ne rtial-confi nement-fusion research c:: 1-11-11iLLNL facilties. Point at upper left represents ments, the fusion energy generated by o ~ 'iii the laser-driven implosion of a the deuterium-tritium will approach the KMS J~ LASL deuterium-tritium hohlraum target of '"41 10 deuterium-tritium thermal energy. Q. n TLASL 10 atm classified design. Radiochemical tech E 1~ o , o +- O -l Figure 4 shows the status and goals o niques showed the density to be 100 u of inertial fusion experiments. The ex KMS li 4- T times that of a liquid deuterium-tritium periments that achieved fuel densities 1---0+ 0-1 mixture. With the Nova laser, re LLNL 11 LLNL searchers plan to implode deuterium 100 times that of the liquid were per 0.1 L-___~ ____~ ___~ tritium to a temperature of several keV formed with the LLNL 1O-k}, I-micron 0.1 10 100 and a density 1000 times that of the Shiv a laser and had a confinement Peak fuel temperature, keV liquid.

21 driver can be designed, funded, and reactors. There has been substantial constructed, we must have have experi progress in all three areas. mental confirmation of theoretical With projected improvements in tar estimates of the required driver get gains, the driver would have to de parameters-particularly the driver's liver an energy of about 2 MJ, a peak energy. The reactor driver is so power of 100 TW, at an efficiency of 10 expensive-perhaps a half billion to 20%. The beams from the driver dollars-that it is not feasible to build it must focus to spots a few millimeters in twice as large as required, to provide a diameter across a 5-m chamber to give 14 15 2 substantial margin for error. Conse a power density of 10 to 10 W/cm . quently, we must generate convincing The coupling between the beam and experimental evidence showing that if the target must be relatively efficient. the reactor-scale driver were con We will need a repetition rate of ten to structed, high target gains would result. twenty implosions per second. The This convincing evidence may be used driver should cost less than $400 as an operational definition of scientific million. feasibility. The candidates for the driver are Physicists will use the Nova laser at KrF, CO2, and free-electron lasers, and LLNL and the light-ion facility at beams of heavy and light ions. We are Sandia, the Particle Beam Fusion optimistic that light ions will be able to 14 2 Accelerator II (PBFA II), to explore sci focus to 10 W/cm . Researchers have entific feasibility. For directly imploded already focused light-ion beams to 12 2 targets, the central core will reach high 10 W/cm . We have not yet achieved

densities and the threshold of ignition. efficient beam-target coupling with CO2 Then, even though the volume of ma lasers. The 40-kJ Antares laser-the terial at this high density will not be world's largest CO2 laser, now under large enough for the burn to propagate construction at Los Alamos-will help in the pellet, it is feasible to diagnose explore this problem. Imaginative tar the important parameters: the density gets are now being tested on the 10-kJ distribution, the temperature, and the CO2 Helios laser at Los Alamos. amount of contamination of the fuel by With current technologies, most of the imploding shell. A series of implo the proposed drivers would cost ap sion experiments will diagnose the im proximately $400IJ, or $800 million for ploding shells. Snapshots will be taken 2 MJ. Many of the candidates are mak with a laser-driven x-ray backlighting ing steady progress in reducing their source. In addition, researchers will ob costs. We foresee a factor-of-two cost serve the surfaces of the imploding reduction to about $200IJ. Light-ion ac shells with optical and x-ray streaking celerators and advanced lasers may be cameras to measure the amount of pre significantly cheaper. When the cost of heating, the velocity history, and the the fraction of the reactor needed to symmetry of the implosion. Finally, power the driver is included, highly ef they will use the Nova to perform ficient drivers such as heavy-ion accel laser-plasma coupling experiments at erators with 25% efficiency may have the scale lengths of the reactor target nearly a twofold cost advantage over plasma. The results of these measure marginally efficient drivers such as ments will allow us to predict with suf lasers with 5% efficiency. The table ficiently high confidence how large a summarizes the status, strengths, and target and driver will be required to weaknesses of the driver candidates. achieve high gain. The Nova and Targets. Both hohlraum and direct PBFA II facilities will be completed in targets are under development. These the mid-eighties. target designs include margins of safety to cover uncertainties in the implosion A Three-Part System and burn. Let us look at each of the key tech Targets for inertial-confinement nologies for inertial-confinement fusion fusion are fabricated from very small power plants: drivers, targets, and masses of low-cost materials (except for

22 DEFENSE PROGRAMS tritium, which is regenerated in the re actor). Target costs, then, are dominated Driver candidates. by the capital and operating costs of the target factory. There are plausible solutions for the principal fabrication Free- CO2 KrF electron Heavy-ion Light-ion problems: surface finish, on-line inspec Requirements laser laser laser accelerator accelerator tion, and high production rate. In hohlraum targets, as we men tioned, the energy of the driver beam is Efficiency (10-20%) ? ? + ++ + Focusing (1016_10 15 W/cm2 absorbed and converted to x rays, at 5 m) + + + + ? which are contained by a radiation case Target coupling (10%) ? ++ ++ ++ + and used to drive the implosion. This Repetition rate (10-20 Hz) + + ++ ++ + gives the hohlraum target one of its im Cost ($200/J at 2 MJ) + + + + ++ portant advantages-improved implo sion symmetry. One can achieve sym +; could meet requirements. metry without requiring the beams of the driver to be uniform and symmetri cally arranged. In some reactor designs, square of its compression, even a 40% just two beams drive the target. It is increase in density would decrease the more difficult to implode directly fuel mass and driver size by a factor of driven targets symmetrically with a few two. beams. Another important advantage of It may also be feasible to make sig hohlraum targets is that they couple ef nificant improvements in the target's ficiently to several of the driver implosion efficiency. Nonablative im candidates-possibly including CO2 plosion schemes may have a higher im lasers. Researchers at LLNL have done plosion efficiency. This could decrease many experiments with hohlraum tar the size of the driver and increase the gets using the I-micron Shiva laser and target gain by a factor of two. the 1-, 1/2-, and I/3-micron Argus Finally, current target designs pro laser. The experimental results are in vide a substantial margin for error. We excellent agreement with detailed may be able to relax these conservative LASNEX calculations and with theoreti design criteria when we have a greater cal scaling relationships. experimental and theoretical under Directly imploded targets appear to standing of the implosion and burning be advantageous at driver energies un of the targets. Such a relaxation could der 100-kJ driver energy. Researchers at provide another factor-of-two decrease KMS, NRL, the University of Rochester, in driver size and increase in target and laboratories outside the U.S. are at gain. tempting to develop directly imploded We hope to achieve a twofold reduc reactor targets with both the required tion in driver energy requirements and implosion symmetry and as high an a twofold increase in target gain. implosion efficiency as that of the hohl Figure 5 relates the performance of raum targets. Implosion efficiency is the the target to driver and reactor require overall energy efficiency with which ments.6 The lower band in this figure the beam couples to the target and shows the calculated gains of our con compresses the fuel. An important servative targets. The optimistic band problem is how to generate and com represents an improvement in target bine many ultrasmooth laser beams or performance by almost a factor of four. ion beams. The design point is at 2 MJ with a yield Significant improvements in targets of 600 MJ-a gain of 300. For a I-GWe for inertial-confinement fusion are pos reactor and and 10 to 20% efficient sible. Compression of the fuel to higher driver, the overall energetics would be density is theoretically possible. Be robust. Driving fusion with a KrF laser cause the scaling parameter for the of 7% efficiency would give a good burn efficiency of the fuel is the prod overall energy gain for optimistic target uct of the mass of the fuel and the performance but only a marginal gain

23 Fig. 5 reactions. Thus, the impulse is reduced 4000 Relationships of performance param a thousandfold because the mass is a eters of target, driver, and reactor for million times smaller. In addition, the a 1-GW. power plant burning lithium is sufficiently massive and far deuterium-tritium fuel. Inertial 2000 from the wall that its interaction with confinement-fusion reactors may be the wall is largely nonimpulsive. economically competitive with light water fission reactors if they can be Radioactive target debris is also an designed to have a 2-MJ driver energy 1000 issue. Any material in the target besides (at a direct cost of $200/ J), 600-MJ ~ 800 deuterium and tritium will be activated target yield, driver efficiency l1d by the intense flux of neutrons. Debris ~ 600 greater than 15%, 5-Hz reactor repe Q) is also activated further when it is recir >= tition rate, and 10- to 20-Hz driver rep culated in the liquid lithium inside the etition rate. The driver would be 400 shared by two to four reactors. reactor. In targets designed to minimize radioactive debris, the most significant radioactive material is lead. The domi 200 15 nant radioactive isotope of lead is lead-203, with a half-life of 53 hours. 20 Other radioactive isotopes are negligi 100 ""-__....:!I£: ___.l....-_.l....---i..--1 ble. A few months after the lead has 1 2 4 6 8 10 been separated from the lithium, the Driver energy, MJ radioactivity has decayed by a large with projected target performance. The factor, and the lead may be recycled in lines of minimum necessary driver effi the target factory. The total mass of ra ciency in Fig. 5 are based on the as dioactive target debris generated during sumption that the product of the effi the 3D-year lifetime of the reactor is a ciency of the driver and the gain of the few tons. target is 20. Then the driver uses 10 to In the HYLIFE scheme (Fig. 1), 15% of the power the reactor produces. beams come to the target from drivers Reactors. A critical issue for inertial that are of about 100 m from the reac confinement fusion reactors is the tion chamber, which has a characteristic pulsed thermonuclear explosion, which dimension about 5 m. The average could cause unshielded reactor walls to product of density and thickness fail by cyclic fatigue or ablation. In the through the pattern of lithium jets is LLNL HYLIFE fluid-wall design (Fig. 1), about 40 g/ cm2. Figure 6 shows the life there is a shower-like set of fluid jets of time of a first wall made of low liquid lithium between the exploding chromium, nickel-free steel as a func target and the first wall. 6 The fluid tion of the thickness of the lithium.6 In layer, 0.5 to 1 m thick, protects the first fusion reactors, at least two neutronic wall from the pulse of radiation and effects reduce the lifetime of the first hot plasma. It also reduces by a factor wall: atomic displacements and the of about 10 to 100 the activation and generation of helium. For a lithium neutron damage in the first wall. thickness of 0.5 m, the first wall's life Another issue2 is the feasibility of time is about 30 years, so it would not containing small thermonuclear explo have to be changed during the lifetime sions, each releasing an energy equal to of the reactor. Without the fluid shield, a few tenths of a ton of TNT. The im the wall would last about five years pulse of an explosion is proportional to and would have to be replaced by re the square root of the product of mass mote control several times during the and energy. Although the energy, life of the reactor. which is mainly radiated into the fluid Because the time required for a curtain by neutrons and x rays, corre splattered droplet to fall 5 m is about sponds to a significant fraction of a ton 1 s, the current HYLIFE design is lim of TNT, the mass of the target is a mil ited to a repetition rate of about 1 Hz. lion times smaller because the energy is To increase the repetition rate to 5 Hz generated by 10-MeV thermonuclear re so that we can fully exploit both high actions rather than by l-eV chemical repetition-rate drivers and the heat

24 DEFENSE PROGRAMS

capacity of the flowing lithium, which fusion systems are estimated to be is several times larger than required, we roughly a factor of two more expensive must improve the design. With evolu than light-water fission reactors. How tionary improvements, 3 Hz may be ever, fusion hybrids would cap any in feasible. Several radical variations crease in the cost of fission energy due would take us beyond that. In the to escalating fission-fuel costs at only HIBALL scheme/ for example, porous 20% of the total cost of the light-water silicon carbide tubes would confine the reactors themselves, because a hybrid streams of liquid lithium-lead alloys. costing as much as three light-water re These tubes would also reduce the actors could supply fuel for 15 light liquid flow rate. water reactors. Furthermore, the Na With respect to feasibility, the con tional Academy of Sciences Committee clusions of the Foster Committee are on Nuclear and Alternative Energy Sys valid: the number of promising ap tems estimates that externalities are not proaches is in reasonable balance with significant. Liquid-metal fast breeder the problems and unknowns, and no reactors would also limit the escalation insurmountable roadblocks are evident. of fission fuel costs.8 Beyond scientific feasibility, a major Nonetheless, because U.s. energy challenge for the inertial-confinement costs are less than 10% of the GNP, our fusion program is to realize the poten society could decide to buy an environ tial advances: higher gain targets with mentally superior energy system cost Fig. 6 reduced driver requirements; cheaper, ing twice as much as a minimum-cost high-efficiency drivers; and fluid-wall energy system. However, U.s. industry First-wall lifetime, as a function of the thickness of the protective liquid lith reactors able to withstand high repe powered by a doubly expensive energy ium curtain. These estimates are for a tition rates. system, employing expensive labor, 2.25 Cr-1.0 Mo-steel wall in a would be less competitive with foreign 10-MW/ m 2 fusion reactor. A half me Utility industry powered by minimum-cost en ter of shielding extends the lifetime We now turn our attention to the ergy systems. This would be particu from a few years to 30 years. Uncer tainties are indicated in the effects of two crucial questions of economic and larly true if foreign industry invested its neutron-induced helium production environmental utility for all approaches energy system cost savings in automa and atomic displacements. The upper to fusion: tion, advanced technology, and re and lower curves for helium produc • In the limit of its best perfor search and development. tion shown here represent 1000 and mance, is fusion economically feasible? An important factor that may make 500 atomic parts per million of helium, respectively. The upper and lower dis • Do fusion's economic and environ possible inertial-confinement fusion placement damage curves represent mental potentials justify accelerated power plants that are economically 330 and 165 displacements per atom, development, particularly in light of the competitive with fission is driver respectively. (From Ref. 6.) possible limitations of coal and fission energy? Unfortunately, fusion's eco 50r------~~~--_rr_------~ nomic and environmental potentials are Displacement not very well known. Nevertheless, I damage will attempt to answer these questions assuming we can achieve scientific fea 40 sibility and the potential advances that Q; o~ we have discussed. c. - 30 Were it not for the potential exis :2 tence of the "fusion hybrid" reactor iii and the liquid-metal fast breeder (JJ ro reactor-the long-term escalation of ~ 20 fossil and fission fuel costs and the cost Q) of externalities such as radioactive . ~ ]1 waste and safety hazards might make :J 10 fusion economically competitive even at twice the cost of current fossil and fission energy systems. Fusion hybrids OL------~------__~ ______~~ ______L______~ __~ produce fuel for fission reactors. Most o 20 40 60 80 100 first-generation inertial and magnetic Thickness of lithium, cm

25 separability, which the Foster Commit they were almost 50% more expensive tee discussed: "One of the chief advan to build. Here is one possible account tages of ICF is that ... the driver is sepa ing of the extra costs: rate from the reactor vessel itself, and • The cost of the driver is less than can be removed some distance. This 20% of the cost of a light-water reactor. means that an ICF reactor may have a This would compensate for the 20% in relatively small containment volume; crease in the cost of fission energy due that its operation, maintenance, and re to the escalation of fuel costs. pair will be relatively simple; and that • The cost of the targets and target the most expensive components will factory is less than 25% of the cost of a not be subject to neutron bombardment light-water reactor. This compensates and activation. The potential also exists for the light-water reactor's 25% fuel for a great variety of power plant sizes cycle expense. The capital cost of the and configurations." Furthermore, a reactor and the rest of the power plant separated driver can drive several reac must not be more than that of a light tors, and time-shared target factories water reactor. are feasible as well. The cost of the driver may be For inertial and magnetic confine reduced to 10 to 20% of the cost ment approaches where time sharing of a I-GWe light-water reactor and fluid walls are not feasible, one can approximately $150 million not includ reduce costs and radioactivity by other ing interest charges. For multimegajoule means, such as developing cheaper short-wavelength lasers and heavy-ion superconducting materials that sustain accelerators, one can achieve such a re higher magnetic fields (to increase the duction by reducing the driver costs power density), and developing first twofold to $200/J at 2 MJ, improving wall materials with longer lifetimes and the targets twofold (to reduce the re less neutron-induced radioactivity. quired driver energy to 2 MJ) and by The high cost of first-generation using a single driver for two or more fusion reactors relative to light-water reactors. We have already discussed fission reactors is principally due to these driver and target improvements. three factors: Multireactor systems with time • The costs of fusion technology shared drivers are apparently feasible. equipment-inertial confinement's Laser and heavy-ion beams can be driver and target factory, or magnetic switched rapidly and propagated over confinement's superconducting magnet, 100-m distances; these drivers are capa beam heater, and high-vacuum system. ble of 10- to 20-Hz repetition rates with • Fusion's lower power density. relatively small increases in cost. Some • Fusion's more complex first-wall high-energy accelerators, from which and heat-transfer structures. heavy-ion technology is derived, show high capacity factors. If a few addi Reducing Costs tional beams are designed into Even if fusion-technology equipment multibeam fusion lasers, then individ were free, some approaches to fusion ual beams could be shut down for re power would be more expensive than pair without affecting the operation of light-water reactor power because of the reactor. A four-reactor site with the second two factors. To be economi 4-GWe total electrical output would cally competitive, the cost premium due generate roughly 1 % of the projected to these three factors must be less than U.s. electrical energy in 2010 and less about 50%-20% for fission fuel escala than 0.5% in 2050, assuming a slow 2% tion and 25% for un escalated fission energy growth rate. fuel-cycle costs. In light-water reactors, Driver technologies such as light-ion fuel-cycle costs are approximately 25% accelerators and advanced lasers may of the total and are not included in cap be cheap enough so that with an addi ital costs. To a first approximation, tional factor-of-two improvement in fusion reactors could compete economi target performance, fusion reactors cally with light-water reactors even if as small as 0.5 GWe would be

26 DEFENSE PROGRAMS

economically competitive with light burning inertial-confinement fusion water reactors. These small reactors system may be significantly cheaper would be highly advantageous for ini than a light-water reactor, depending tial commercialization. on the size of the driver required to The estimated capital and operating achieve high gains with deuterium cost of the target factory is 10 to 30% of burning targets. the cost of a light-water reactor.7 Sev Attractive fusion-fission hybrids and eral factors limit the cost. These include hydrogen synfuel producers are also the factory's small size, complete auto feasible-hybrids, because neutron and mation, and long-term high production tritium breeding is possible within the rates, as well as its location at the first wall, and synfuel producers, be power plant and the automated trans cause reactors with walls at very high port of pellets to the reactor chamber. temperatures may be feasible.9 The capital cost of a HIBALL fluid reactor and the rest of the power plant Options for the Future without the driver and target factory is There are major uncertainties in our estimated to be approximately equal to understanding of the CO2 greenhouse the capital cost of a light-water reactor? problem. However, if calculations are Inertial-confinement fusion reactors correct, before the middle of the 21st may have an exceptionally high capac century it may be highly desirable to ity for optimization. The target is small rely on nonfossil fuels to generate more and cheap and may be improved dur than 50% of the total energy. U.S. fis ing the lifetime of the reactor. The sion energy could not be accelerated driver and target factory, being separate rapidly enough to sustain historic eco from the reactor, are not strongly acti nomic growth rates, and is now in the vated by the fusion neutrons. Utility process of losing its competitive bankrupting meltdown accidents are advantage. not possible when the reactor is One option would be to accept switched off. Based on our experience slower economic growth and the asso with fission reactors, this potential for ciated loss in GNP. incorporating technological advances A second option would be to import and responding gracefully to Murphy's uranium and zero-defect, low-cost Law is important for the development "Toyota" and "VW" fission reactors. of practical high-technology power These two options would be extraordi plants. narily expensive, costing many trillions Deuterium-burning reactors would of dollars over several decades. have significant environmental advan A third option would be to counter tages over deuterium-tritium reactors act the warming caused by the green and might also be cheaper. The radio house effect with global climate activity of the first wall would be re control-seeding the stratosphere with duced because fusing deuterium pro aerosals to increase Earth's albedo, for duces fewer and less energetic example. lO The greenhouse warming neutrons. To eliminate the tritium gen due to the projected doubling of the erated in the liquid-lithium curtain, one CO2 in the atmosphere might be would protect the first wall with a ma counteracted by increasing the albedo terial such as liquid lead. By eliminat by 2%. Global climate control would ing the lithium and minimizing the tri require an unprecedented degree of in tium hazard and first-wall radioactivity, ternational cooperation. The best strat fusion would approach its full environ egy might be to intensify energy con mental potential. Because the fuel burn servation, revitalize the U.S. fission occurs inside the target and because industry, and accelerate the develop fewer neutrons are produced, deute ment of economically competitive rium-burning inertial-confinement fusion and solar energy. fu sion reactors would have a higher Figure 7 shows the results of a re power density than deuterium-tritium cent calculation of the CO2 greenhouse burning reactors. Such a deuterium- effect by NASA scientists.ll Their

27 Coal burning will also cause serious

4 environmental problems such as acid rain. (.) '0 Because it takes 40 years to install a oN !II new energy technology, the candidates Q) ::!: to replace fossil fuels should be demon strated in this century. The most highly Nonfossil replacement developed candidate is fission. An im fuels portant question is, could fission meet U.s. energy needs by 2030? The U.s. fission industry is being crippled by Murphy's Law. No new domestic or ders for reactors are projected for 5 to Observations 10 years. The probability of a reactor 0 .....-..,... disabling (and utility-bankrupting?) ac cident is estimated to be as high as one 1950 2000 2050 2100 in thirty per reactor lifetime. Alvin Year Weinberg has called for the develop ment of a second-generation light water reactor, 10 to 100 times more Fig. 7 model predicts the average increase in reliable than current designsY 13 Projected average global temperature global temperature due to CO2 from A recent study by TRW and LLNL the burning of fossil fuel. The calcula scientists-including Teller, a leading change due to CO 2 produced in the combustion of fossil fuels. The tem tions indicate that the temperature in proponent of the coal-fission energy perature is expected to rise above the crease will become observable in the strategy-concluded that with moderate background noise in the time period period 1990 to 2000. With slow (2%) energy growth rates fission could gen 1990 to 2000. The graph shows the results of various economic growth energy growth rates and no reduction erate only about 15% of the total U.S. rates and strategies of fuel use. The in the use of coal, the temperature in energy by 2040. Inspection of these cal upper and lower slow-growth .curves creases 2.5 °C by 2100. If coal burning is culations shows that with either slow represent results of calculations as phased out in the period 2020 to 2060, (2%) energy growth rates and limited suming no coal phaseout and a coal the temperature increase is only 1.5 °C. energy conservation or with historic phaseout beginning in the year 2020, respectively. "Business as usual" sce This is not much more than the 1°C energy growth rates and 'continuing narios generate average temperatures temperature increase that is predicted improvements in conservation, fission approaching those of the dinosaur to occur because of the CO2 already could generate only about 30% of the age. In the slow-energy-growth sce added to the atmosphere. When we U.S. energy by 2040 to 2050. With both nario, the temperature increase may take into account the warming due to slow growth and strong conservation, be limited to 1.5°C by starting to phase out coal burning fairly early in both CO2 and trace gases, the time to fission energy would be adequate. Fis the 21st century. (From Ref. 11.) begin phasing out the burning of coal sion energy has a limited rate of accel may advance 20 years to the early 21st eration because of the 10- to 20-year century. doubling time of liquid-metal fast Optimists argue that the net green breeder reactors, the finite U.s. supply house effect may be beneficial. Part of of fuel for light-water reactors, and the USSR might become viable farm realistic deployment rates for a newly land, although part of the U.S. prime developed fast-breeder-reactor technol middle western farmbelt may become ogy. Because one fusion-fission hybrid drought-prone. The growing season could support 15 light-water reactors, would lengthen and plants might grow an accelerated hybrid program in faster. Melting of the West Antarctic ice conjunction with a revitalized, cap and flooding of the world's coastal competitive U.S. fission industry could cities probably would not occur in the generate 50% of the total U.s. energy 21st century. However, while the rate by 2030, even assuming historic of change of climate may be difficult growth rates. even for affluent civilizations, it could The projected international energy be disastrous for underdeveloped problem is much more severe than the nations with populations that already U.s. problem. In the next 50 years, border on starvation. rapid international energy growth will

28 DEFENSE PROGRAMS

be driven by a doubling of the popula major commitment of our scientific and tion and steady per capita energy technological resources. L\\!II growth. Energy demand is projected14 to increase three- to fourfold. This would require a tenfold increase in coal production and/or 10 000 nuclear reac Notes and References tors. The market for practical fusion re 1. J. S. Fos ter, Jr., "The Promi se of ICF Power," presented at the AAAS Annual Meeting, actors would be on the order of $10 January 1980. trillion. In comparison to the 2. W. D. Metz, Science 212, 517 (1981). multitrillion-dollar costs associated with 3. W. C. Mead, E. M. Campbell, el 01., Phys. these various options, the estimated $20 Rcv. Lett. 47, 18 (1 981). billion cost of fusion development is 4. W. Seka, R. S. Craxton, J. Delettrez, et 01., Optics COIl1I11 40, 437 (1982); N. G. Basov, relatively small. A. R. Za ri tskii, S. D. Zakharov, et 01., Soviet f. In the 1980s, the magnetic and Qllant. Electron., 2, 439, 1973; C. Garban inertial-confinement fusion programs Labaunc, E. Fabre, C. E. Max, et al ., Phys. will develop an improved understand Rev. Lel t., 48, # 15, 101 8, 1982; D. C. Slater, ing of fusion's economic and environ Gar. E. Busch, G. Chartis, el al., Phys. Rev. Lett.,46, 18 (1981). mental potentials. There should be a 5. C. E. Max and K. G. Estabrook, "Comments" coordinated management of these pro Plasma Physics, S, 239 (1980). grams with a common basis for pro 6. M. Monsler, J. Hovingh, D. L. Cook, T. G. gram planning and evalution. Based on Frank, and G. A. Moses, Nuclear Techno logy/ our present incomplete understanding, I Fus ion, 1,302 (1981). 7. R. Badger et al ., HI BALL, Rept. UWFDM - believe the answers to the two crucial 450/KfK -3202, University of Wisconsin questions of utility are positive: eco (198 1). nomically competitive fusion systems 8. Nati onal Academy of Sciences, Energy ill are potentially feasible, and the acceler Trans itioll, 1985- 2000, Freeman, San Fran ated development of fusion is justified cisco (1 980). 9. R. W. Conn ct al ., Rept., UWFDM-220, Uni by fusion's economic and environmen versity of Wisconsin (1 977). tal potentials, especially in light of the 10. M. I. Bud yko, Meteorologiyai Grdrologiya, significant limitations of coal and fis No.2 (1974). sion energy. 11. J. Hansen, D. Johnson, ct al ., Science, 213, 957 Because of the limitations of the (1 981). 12. A. Wein berg, Science, 82, 16 (1 982). coal-fission strategy, we may need 13. J. Mani scalco, D. H. Berwald, R. W. Moir, J. fusion and other alternative energy D. Lee, Edward Tell er, et al., The Fusion Fuel sources by the early 21st century. The Factory - An Early Application of Nuclear U.S. fusion program should be acceler Fusioll Thai Makes Se nse, Lawrence liver ated to develop practical power plants more National Laboratory, Rept. UCRL- 87801 (1 982). on this timescale. 14. J. Anderer, W. Hafele, et aI., "Energy in Fi The development of fusion energy ni te Wo rl d," Ba lli nger, Cambridge, MA merits high national priority and a (1981).