Commercial Fusion Reactor Research Articles

Intense light-ion beams provide a robust, common-driver path toward ignition, gain, and commercial fusion energy

Intense light-ion beams are being developed for investigations of inertial confinement fusion (ICF). This effort has concentrated on developing the Particle Beam Fusion Accelerator II (PBFA II) at Sandia as a driver for ICF target experiments, on design concepts for a high-yield, high-gain Laboratory Microfusion Facility (LMF), and on a comprehensive system study of a light-ion beam-driven commercial fusion reactor (LIBRA). This article reports on the status of design concepts and research in these areas.

Small-angle neutron scattering studies of irradiated metallic materials

The study of microstructural radiation damage in metallic materials is of utmost importance in a large variety of technical fields related to energy production plants; more specifically the availability of radiation resistant alloys is at present considered as a key issue for the development of commercial fusion reactors. Since its earliest applications, Small-angle neutron scattering (SANS) has provided an effective investigation tool characterizing in a nondestructiveway the presence and the evolution of microstructural defects associated with radiation damage in pure metals and technical alloys. The main SANS studies in this domain are reviewed. including the most recent results of a research programme concerning the characterization of He-bubble growth in a martensitic steel proposed as structural material for fusion reactors (MANET).

A Novel superconducting toroidal field magnet concept using advanced materials

The plasma physics database indicates that two distinct approaches to tokamak design may lead to commercial fusion reactors: low Aspect ratio, high plasma current, relatively low magnetic field devices, and high Aspect ratio, high field devices. The former requires significant enhancements in plasma performance, while the latter depends primarily upon technology development. The key technology for the commercialization of the high-field approach is large, high magnetic field superconducting magnets. In this paper, the physics motivation for the high field approach and key superconducting magnet (SCM) development issues are reviewed. Improved SCM performance may be obtained from improved materials and/or improved engineering. Superconducting materials ranging from NbTi to high-Tc oxides are reviewed, demonstrating the broad range of potential superconducting materials. Structural material options are discussed, including cryogenic steel alloys and fiber-reinforced composite materials. Again, the breadth of options is highlighted. The potential for improved magnet engineering is quantified in terms of the Virial Theorem Limit, and two examples of approaches to highly optimized magnet configurations are discussed. The force-reduced concept, which is a finite application of the force-free solutions to Ampere's Law, appear promising for large SCMs but may be limited by the electromagnetics of a fusion plasma. The Solid Superconducting Cylinder (SSC) concept is proposed. This concept combines the unique properties of high-Tc superconductors within a low-Tc SCM to obtain (1) significant reductions in the structural material volume, (2) a decoupling of the tri-axial (compressive and tensile) stress state, and (3) a demountable TF magnet system. The advantages of this approach are quantified in terms of a 24 T commercial reactor TF magnet system. Significant reductions in the mechanical stress and the TF radial build are demonstrated.

Tokamak poloidal field power supplies

The present generation of large tokamak experiments all make large electric power demands to supply their four main pulsed loads (toroidal field coils, poloidal field coils, poloidal field amplifiers and additional heating). These individual load requirements are described for three tokamaks, and the overall pulses are compared with the capabilities of their external bulk power supply systems. The technical and economic arguments for supplying the poloidal field coils from flywheel-generator-convertors are discussed. Typical poloidal field current and voltage requirements are described, and are seen to involve the removal of magnetic energy at very high power levels during one of the five phases of a tokamak's operation. This is conveniently achieved by using DC interrupters to divert the current into discharge resistors, and the techniques available for DC interruption are reviewed. The complete poloidal field power supply circuit is described, including its performance during each of the five phases. Seven fault conditions are identified and their impact on the design is discussed. The influence of the rectifier on the generator design and performance is examined, with particular reference to the harmonics. In concluding, mention is made of future commercial fusion reactors and their power supplies.

Trends in fusion reactor safety research

Fusion has the potential to be attractive energy source. From the safety and environmental perspective, fusion must avoid concerns about catastrophic accidents and unsolvable waste disposal. In addition, fusion must achieve an acceptable level of risk from operational accidents that results in public exposure and economic loss. Finally, fusion reactors must control routine radioactive effluent, particularly tritium. Major progress in achieving this potential rests on development of low-activation materials or alternative fuels. The safety and performance of various material choices and fuels for commercial fusion reactors can be investigated relatively inexpensively through reactor design studies. These studies bring together experts in a wide range backgrounds and force the group to either agree on a reactor design or identify areas for further study. Fusion reactors will bistributed radioactive inventories. The next generation of experiments will be critical in demonstrating that acceptable levels of safe operation can be achieved. These machines will use materials which are available today and for which a large database exists (e.g. for 316 stainless steels. Researchers have developed a good understanding of the risks associated with operation of these devices. Specifically, consequences from coolant system failures, loss of vacuum events, tritium releases, and liquid-metal reactions have been studies. Recent studies go beyong next-step designs and investigate commercial reactor concerns including tritium release and liquid metal reactions.

Hydrogen transport behavior of metal coatings for plasma-facing components

Plasma-facing components for experimental and commercial fusion reactor studies may include cladding or coatings of refractory metals like tungsten on metallic structural substrates such as copper, vanadium alloys and austenitic stainless steel. Issues of safety and fuel economy include the potential for inventory buildup and permeation of tritium implanted into the plasma-facing surface. This paper reports on laboratory-scale studies with 3 keV D + 3 ion beams to investigate the hydrogen transport behavior in tungsten coatings on substrates of copper. These experiments entailed measurements of the deuterium re-emission and permeation rates for tungsten, copper, and tungsten-coated copper specimens at temperatures ranging from 638 to 825 K and implanting particle fluxes of approximately 5 × 10 19 D/m 2 s. Diffusion constants and surface recombination coefficients with enhancement factors due to sputtering were obtained from these measurements. These data may be used in calculations to estimate permeation rates and inventory buildups for proposed diverter designs.

Helium Pumping Strategies for D-T Fusion Devices

In order for the new generation of long pulse D-T (deuterium-tritium) burning tokamaks to be successful, it is necessary to minimize the helium “ash” that accumulates during the thermonuclear burn. Since tritium is radioactive as well as relatively expensive, the tritium inventory stored at any given facility must also be minimized. It is therefore necessary either to preferentially remove the helium from the plasma, or to recycle all of the gas, extracting the deuterium and tritium for reuse as fuel. This latter approach requires incorporating a high pumping speed and correspondingly large pumping ducts into the fusion device design, as well as an external facility for separating helium from the D-T fuel. Since the He/H ratio in the plasma should not exceed ~5%, the pumping speed must be 20 times higher than required for a system which removes the helium only. The resulting complexity of the pumping system and the need to handle large quantities of tritium imposes a cost penalty of ~100M$ for a typical commercial fusion reactor design. It is therefore desirable to design a pumping system which removes helium only, leaving the D-T fuel in the fusion device. Recall, however, that existing pumping technologies generally provide better pumping of hydrogen, and many pump designs are totally ineffective at pumping helium.Despite the low solubility of helium in many metals, permanent trapping of helium atoms occurs at defect sites, culminating ultimately in the formation of helium bubbles. Retention of trapped inert gas is determined by diffusional processes and is consequently temperature-dependent. Hydrogen has not only a much higher solubility, but also a much higher diffusion coefficient than helium in most metals. Consequently, it is to be expected that for some metals, there is a temperature range in which implanted hydrogen is released much more quickly than implanted helium. Brooks and Mattas proposed using this “self-pumping” effect as the basis for a pump which preferentially removes helium in the presence of hydrogen.

Advances in Commercial ICF Technology Since 1986

Progress in the march toward commercial ICF fusion reactors has been uneven in the past few years. Considerable advances have been made in the area of light ion beam fusion through the development of rep ratable drivers (i.e., HERMES-III technology) and diodes (i.e., applied B configuration with renewable Li surfaces). Significant progress in the development of lasers to compress targets has also been made through the KrF Aurora program. The possibility of lowering the cost of glass in the advanced solid state lasers has been given serious consideration. The development of the Induced Spatial Incoherence (ISI) technique to improve the uniformity of the laser beam has allowed physicists and engineers to once again contemplate the use of symmetric illumination. This would reduce the driver energy required to achieve high gains but it also introduces difficulty in the reactor design. Relatively little progress in commercial heavy ion beam drivers has been made over the past few years aside from an indepth study (HIFSA) of the desirable operating regimes to be pursued. Other areas where little progress has been made are conceptual reactor studies, target declassification and specific experimental programs to address commercial ICF reactor technology needs.

Poloidal Field System Analysis and Scenario Development for ITER

ITER, the International Thermonuclear Experimental Reactor, is a collaborative design by the United States, Europe, Japan and the Soviet Union of a tokamak fusion reactor that would demonstrate the physics and test the technology needed for commercial fusion reactors. The poloidal field (PF) magnets are responsible for forming and shaping highly elongated, high current plasma, during a long-pulse burn. At least two classes of experiments must be supported by the PF system design, including inductively-driven, long-pulse burning discharges and discharges with steady-state current drive.

Study of the neutron spectrum in the test section of fusion engineering test facility based on mirror confinement (FEF)

Abstract The cylindrical plasma in the central cell of the mirror based fusion engineering test facility FEF is used as the 14 MeV neutron source for the fusion engineering tests. The tests are mainly irradiation tests to investigate the behavior of first wall materials and blanket components irradiated by 14 MeV neutrons. The irradiation tests which are assumed to be conducted in the FEF are as follows: (1) material irradiation tests, (2) tritium breeding tests, (3) blanket engineering tests, (4) integrated test under fusion reactor conditions. The following tests are also considered for utilization of the neutron source, (a) fissile fuel production test, (b) isotope production test, (c) nuclear waste annihilation test. The spatial distributions of the intensity of the neutron flux and its energy spectra and that of the gamma ray flux in the test section of FEF have been calculated by using the ANISN code. These calculations were needed to investigate the dependence of the neutron spectrum on the coolant materials of the first wall and the type of reflector. It was found that lead was an optimum choice for the reflector and that the total fluxes of the neutrons at the capsule and loop regions were 6.3 × 1014 n/cm2s and 5.4×1014 n/cm2s respectively. The flux in the capsule region could be as high as 1 × 1015 n/cm2s in the specially designed test section. The energy spectrum found was close to that of a commercial fusion reactor.

Neutron-lean fusion reactor studies for thermal plasmas

The attractiveness of various advanced fusion fuel cycles for use in commercial fusion reactors is investigated. A plasma and reactor simulation code and a nuclear data library were developed for that porpose. Under the basic assumption of a two-component plasma (thermalized bulk plasma and suprathermal reaction products), lithium and boron were found not to qualify as fuel components because of their poor power performance. For (semi-)catalyzed D and for D- 3He, a reasonably large window was identified in parameter space for which the overall energy balance is positive. Various “attractiveness indicators” (neutron load, tritium, etc.) are evaluated and compared to the corresponding values for D-T fueled reactors.

Heavy-Ion Fusion Systems Assessment Implications for Reactors

The requirements, desirable characteristics, trade-offs, and design constraints are discussed for commercial heavy-ion fusion (HIF) reactor plants with induction linear accelerator (Linac) drivers. The trade-offs and the design constraints when the reactor plant requirements and desirable characteristics conflict with those for other HIF power plant systems are described. The reactor plant concepts included in the Heavy-Ion Fusion Systems Assessment (HIFSA) are discussed in relation to these requirements, characteristics, trade-offs, and constraints. Four reactor plant concepts were included in the HIFSA studies to provide large ranges of reactor repetition rate and target yield accommodation (1 to 20 Hz and 150 to 3000 MJ). This permitted thorough exploration of the impact on HIF cost of electricity (COE) of the high repetition rate and efficiency advantages of induction Linacs. Contrary to pre-HIFSA expectations, large plants with large driver repetition rates and multiple reactors are not required for attractive COE: Repetition rates <10 Hz in 1000-MW(electric) one-reactor plants are competitive. More than one HIF reactor plant concept shows promise: The minimum COE estimates for the four concepts in 1000-MW(electric) plants range from 55 to 75 mill/kW-h. Cost and/or technological problems in one part of reactor operating parameter space need not be fatal for HIF: The estimated COE is within 5% of the minimum over wide ranges of the repetition rate and the target yield for a fixed plant size and reactor concept.

Introduction to magnetic fusion reactor design.

Trend of the tokamak reactor design works so far carried out is reviewed, and method of conceptual design for commercial fusion reactor is critically considered concerning the black-box concepts. System-framework of the engineering of magnetic fusion (commercial) reactor design is proposed as four steps. Based on it the next design studies are recommended in parallel approaches for making real-overcome of reactor material problem, from the view point of technological realization and not from the economical one. Real trials are involved.

Review of the research on heliotrons

A brief history of the heliotron, one of the promising candidates for a commercial fusion reactor, is given. The heliotron device can be operated in steady state, since it has a stable magnetic field with high rotational transform and high shear and without ohmic current in the plasma. The results of experimental and theoretical studies on heliotron devices are reported, and future prospects are given. >

Fusion's $372-Million Mothball

Lawrence Livermore National Laboratory's Mirror Fusion Test Facility (MFTF-B) was built to prove that a design using magnetic mirrors could compete in an international race to produce a commercial fusion reactor. The MFTF-B was to be used to propel the magnetic mirror program into a real contest against Livermore's arch rival: the Princeton Plasma Physics Laboratory and its tokamak machine. On 21 February 1986, after 9 years of construction and $372 million, MTFT-B was officially dedicated. However, due to budget restriction DOE demanded the facility be put on standby the very next day.

An Evaluation of Polarized Fuels in a Commercial Deuterium/Tritium Tokamak Reactor

The benefits and limitations arising from the use of polarized deuterium-tritium fuels are assessed for commercial tokamak fusion reactors. The difference in capital costs for a reactor with and without polarized fueling is quantified for two reactors, one with a beta of 0.067 and a major radius of 7 m and the second with a beta of 0.25 and a major radius of 5.25 m. The change in reactor performance is also quantified. The conclusion is that the sum of all benefits associated with the use of polarized fuels does not result in a significant improvement in the tokamak reactor economics.

Nitrate-Salt-Cooled Blanket Concepts

Molten nitrate and nitrate/nitrite salt-cooled blankets have the unique property of low-pressure operation when compared to other potential blanket coolants. Tokamak and mirror blanket designs have been developed with draw salt coolant, a lithium aluminate breeder, and a beryllium multiplier in an HT-9 ferritic steel structure. These blankets have outstanding economic performance and good engineering feasibility. The most evident problem is the high activation of this coolant, which affects system safety. There are also several critical data needs that must be resolved by experiment. This class of coolants merits further consideration for commercial fusion reactors.

A comparison of pulsed and steady-state tokamak reactor burn cycles. Part II: Magnet fatigue, power supplies, and cost analysis

Pulsed operation of a tokamak reactor imposes cost penalties due to such problems as mechanical fatigue and the need to periodically transfer large amounts of energy to various reactor components. This study focuses on lifetime limitations and capital costs of reactor subsystems in an attempt to quantify sensitivity to pulsed operation. Major problem areas include: fatigue in pulsed poloidal field coils; out-of-plane bending fatigue in toroidal field coils; electric power supply costs; and noninductive current driver costs. A capital cost comparison is made for tokamak reactors operating under the four distinct operating cycles which have been proposed. Since high availability and a low cost of energy will be mandatory for a commercial fusion reactor, we can characterize improvements in physics and technology which will help achieve these goals for different burn cycles. A key conclusion is that steady-state operation is likely to result in the least expensive tokamak reactor (perhaps 20% cheaper than the best pulsed reactor), provided noninductive current drive efficiency can be increased roughly four-fold over present-day experimental results.

A comparison of pulsed and steady-state tokamak reactor burn cycles. Part II: Magnet fatigue, power supplies, and cost analysis

Pulsed operation of a tokamak reactor imposes cost penalties due to such problems as mechanical fatigue and the need to periodically transfer large amounts of energy to various reactor components. This study focuses on lifetime limitations and capital costs of reactor subsystems in an attempt to quantify sensitivity to pulsed operation. Major problem areas include: fatigue in pulsed poloidal field coils; out-of-plane bending fatigue in toroidal field coils; electric power supply costs; and noninductive current driver costs. A capital cost comparison is made for tokamak reactors operating under the four distinct operating cycles which have been proposed. Since high availability and a low cost of energy will be mandatory for a commercial fusion reactor, we can characterize improvements in physics and technology which will help achieve these goals for different burn cycles. A key conclusion is that steady-state operation is likely to result in the least expensive tokamak reactor (perhaps 20% cheaper than the best pulsed reactor), provided noninductive current drive efficiency can be increased roughly four-fold over present-day experimental results.

Radiation Safety Criteria for Maintenance and Waste Management in the Mirror Advanced Reactor Study

The Mirror Advanced Reactor Study (MARS) was a 2-yr study of designs for a commercial tandem mirror fusion reactor. Two of the goals of the MARS program were to exploit the full potential of fusion for occupational and environmental safety during operation and maintenance and to realize safe long-term disposal of radioactive wastes. Two numerical ratings devised to characterize materials with respect to impacts of induced radioactivity on these two goals are described. The ratings devised for these purposes are the remote maintenance rating and the waste disposal rating. The MARS reactor designers had these ratings available and used them as guidelines in making configuration and materials choices. Significant differences in meeting these goals were identified, depending on the materials chosen. The final MARS design fully utilized the technology available today and, in large measure, achieved the stated goals of the program.