Kenneth R. Schultz

Exploring the Competitive Potential of Magnetic Fusion Energy: The Interaction of Economics with Safety and Environmental Characteristics

The Senior Committee on Environmental, Safety, and Economic Aspects of Magnetic Fusion Energy (ESECOM) summarizes its recent assessment of magnetic fusion energys (MFEs) prospects for providing energy with economic, environmental, and safety characteristics that would be attractive compared with other energy sources (mainly fission) available in the time frame of the year 2015 and beyond. Accordingly, ESECOM has given particular attention to the interaction of environmental, safety, and economic characteristics of a variety of magnetic fusion reactors, and compared those fusion cases with a variety of fission cases. Eight fusion cases, two fusion-fission hybrid cases, and four fission cases are examined, using consistent economic and safety models, to permit exploration of the environmental, safety, and economic potential of fusion concepts using a wide range of possible materials choices, power densities, power conversion schemes, and fuel cycles.

Lower Activation Materials and Magnetic Fusion Reactors

Radioactivity in fusion reactors can be effectively controlled by materials selection. The detailed relationship between the use of a material for construction of a magnetic fusion reactor and the materials characteristics important to waste disposal, safety, and system maintainability has been studied. The quantitative levels of radioactivation are presented for many materials and alloys, including the role of impurities, and for various design alternatives. A major outcome has been the development of quantitative definitions to characterize materials based on their radioactivation properties. Another key result is a four-level classification scheme to categorize fusion reactors based on quantitative criteria for waste management, system maintenance, and safety. A recommended minimum goal for fusion reactor development is a reference reactor that (a) meets the requirements for Class C shallow land burial of waste materials, (b) permits limited hands-on maintenance outside the magnets shield within 2 days of a shutdown, and (c) meets all requirements for engineered safety. The achievement of a fusion reactor with at least the characteristics of the reference reactor is a realistic goal. Therefore, in making design choices or in developing particular materials or alloys for fusion reactor applications, consideration must be given to both the activation characteristics of amorexa0» material and its engineering practicality for a given application.«xa0less

Materials analysis of the TITAN-I reversed-field-pinch fusion power core

Abstract The operating conditions of a compact, high-neutron-wall-loading fusion reactor severely limit the choices for structural, shield, insulator, and breeder materials. In particular the response of plasma-facing materials to radiation, thermal and pressure stresses, and their compatibility with coolants are of primary concern. Material selection issues are investigated for the compact, high mass-power-density TITAN-I reactor design study. In this paper the major findings regarding material performance are discussed. The retention of mechanical strength at relatively high temperatures, low thermal stresses, and compatibility with liquid lithium make vanadium-base alloys a promising material for structural components. Based on limited data, the thermal creep behaviour of Vue5f83Tiue5f8ISi and Vue5f815Crue5f85Ti alloys is approximated using the modified minimum committment method. In addition, the effects of irradiation and helium generation are superimposed on the creep behavior of Vue5f83Tiue5f81Si. Coolant compatibility issues are investigated. The liquid lithium compatibility of the two vanadium alloys, Vue5f815Crue5f85Ti and Vue5f83Tiue5f81Si, are compared, and the latter was chosen as the primary structural-material candidate for the liquid-lithium-cooled TITAN-I reactor. Electrically insulating materials, capable of operating at high temperatures are necessary throughout the fusion reactor device. Electrical insulator-material issues of concern include irradiation induced swelling and conductivity. Both issues are investigated and operating temperatures for minimum swelling and dielectric breakdown strength are identified for spinel (MgAI 2 O 4 ).

Updated reference design of a liquid metal cooled tandem mirror fusion breeder

The current version of a reference design for a liquid-metal-cooled tandem mirror fusion breeder (fusion-fission hybrid reactor) is summarized. The design update incorporates the results of several recent studies that have attempted to resolve key technical issues that were associated with an earlier reference design completed in 1982. The issues addressed relate to the following areas of design and performance: nuclear performance, magnetohydrodynamic (MHD) pressure loading, beryllium multiplier lifetime, structural efficiency and lifetime, reactor safety, corrosion/mass transfer, and fusion breeder capital cost. The updated blanket design provides increased performance and reduced technological risk in comparison with earlier fission-suppressed hybrid blanket designs. Specifically, the blanket is expected to achieve a net fissile breeding ratio (per fusion) of 0.84, with a tritium breeding ratio of 1.06, and an average blanket energy multiplication of 2.44. It would operated at a relatively low neutron wall loading (1.7 MW/m/sup 2/) with a low lithium coolant outlet temperature (425/sup 0/C).

Blanket design for the ARIES-I tokamak reactor

For the Advanced Reactor Innovation and Evaluation Study-I (ARIES-I) tokamak power reactor design, the authors evaluated two gas-cooled, low-activation ceramic blanket designs, a 5-MPa helium-cooled design, and a 0.5-MPa CO/sub 2/ gas-carried, Li/sub 4/SiO/sub 4/ particulate design. The more extensive database available for the helium-cooled option has prompted the selection of this option as the reference design. The selected ARIES-I blanket design uses SiC composite as the structural material, 5-MPa helium as coolant, Li/sub 4/SiO/sub 4/ as the solid tritium breeder, and Be metal pellets as the neutron multiplier. This combination of materials provides the design of a high nuclear performance blanket with high-outlet temperature, good neutron multiplication, and adequate tritium breeding. It is a low-activation design that satisfies the criteria for 10CFR61 Class-C shallow land waste disposal, and achieves inherent safety since it produces negligible after heat, thus virtually eliminating the possibility of exposing the public to radioactivity. The mechanical design, neutronics analysis, thermal-hydraulic analysis, power-conversion system design, tritium extraction, and safety evaluation are summarized.<<ETX>>

Helium-Cooled Blanket Designs

A systematic selection and evaluation of helium-cooled blanket concepts has been performed as part of the Blanket Comparison and Selection Study (BCSS). Helium-cooled Li/sub 2/O, lithium, LiAlO/sub 2//Be, and Flibe/Be blanket concepts were selected for detailed design and evaluation. These concepts are applicable to both tokamak and tandem mirror reactors (TMRs). The design and analysis of Li/sub 2/O, lithium, and LiAlO/sub 2//Be blanket concepts are presented. Previous blanket designs were studied and the pressurized lobe configuration was selected for the helium-cooled BCSS designs. Fifty-four different combinations of structural, breeder, and neutron multiplier materials were considered and four helium-cooled blanket concepts were selected for detailed design and evaluation. Mechanical, thermal, and neutronic designs were developed, and tritium control methods were specified. In the final BCSS evaluation, the Li/sub 2/O blanket design ranked second for tokamaks and third for TMRs. The lithium blanket design ranked third for tokamaks and fourth for TMRs. To help guide future research and development, the critical issues associated with each of the helium-cooled designs were identified and necessary experimental data highlighted. These data include irradiation behavior of the blanket materials, compatibility between the structure and liquid-metal breeder materials, and the behavior of tritium in a helium-cooled blanket morexa0» environment. The designs offer favorable performance, design simplicity, and attractive safety features for fusion reactors. Design improvements were identified that could allow still better performance of the helium-cooled blanket designs. «xa0less

Introduction and synopsis of the TITAN reversed-field-pinch fusion-reactor study

Abstract The TITAN reversed-field-pinch (RFP) fusion-reactor study has two objectives: to determine the technical feasibility and key developmental issues for an RFP fusion reactor operating at high power density: and to determine the potential economic (cost of electricity), operational (maintenance and availability), safety and environmental features of high mass-power-density fusion-reactor systems. Mass power density (MPD) is defined as the ratio of net electric output to the mass of the fusion power core (FPC). The FPC includes the plasma chamber, first wall, blanket, shield, magnets, and related structure. Two different detailed designs TITAN-I and TITAN-II, have been produced to demonstrate the possibility of multiple engineering-design approaches to high-MPD reactors. TITAN-I is a self-cooled lithium design with a vanadium-alloy structure. TITAN-II is a self-cooled aqueous loop-in-pool design with 9-C ferritic steel as the structural material. Both designs use RFP plasmas operating with essentially the same parameters. Both conceptual reactors are based on the DT fuel cycle, have a net electric output of about 1000 MWe, are compact, and have a high MPD of 800 kWe per tonne of FPC. The inherent physical characteristics of the RFP confinement concept make possible compact fusion reactors with such a high MPD. The TITAN designs would meet the U.S. criteria for the near-surface disposal of radioactive waste (Class C, IOCFR61) and would achieve a high Level of Safety Assurance with respect to FPC damage by decay afterheat and radioactivity release caused by accidents. Very importantly, a “single-piece” FPC maintenance procedure has been worked out and appears feasible for both designs. Parametric system studies have been used to find cost-optimized designs. to determine the parametric design window associated with each approach, and to assess the sensitivity of the designs to a wide range of physics and engineering requirements and assumptions. The design window for such compact RFP reactors would include machines with neutron wall loadings in the range of 10–20 MW/m 2 with a shallow minimum COE at about 18 MW/m 2 . Even though operation at the lower end of the this range of wall loading (10–12 MW/m 2 ) is possible, and may be preferable, the TITAN study adopted the design point at the upper end (18 MW/m 2 ) in order to quantify and assess the technical feasibility and physics limits for such high-MPD reactors. From this work, key physics and engineering issues central to achieving reactors with the features of TITAN-I and TITAN-II have emerged.

The TITAN-II reversed-field-pinch fusion-power-core design

Abstract The TITAN reversed-field-pinch (RFP) fusion-reactor study has two objectives: to determine the technical feasibility and key developmental issues for an RFP fusion reactor operating at high power density; and to determine the potential economic operational, safety, and environmental features of high mass-power-density (MPD) fusion-reactor systems. Parametric system studies have been used to find cost-optimized designs. The design window for compact RFP reactors includes the range of 10–20 MW/m2. The reactors are physically small, and a potential benefit of this “compactness” is improved economics. The TITAN study adopted 18 MW/m2 in order to assess the technical feasibility and physics limits for such high-MPD reactors. The TITAN-I design is a lithium self-cooled design with a vanadium-alloy (V-3Ti-1Si) structural material. The magnetic field topology of the RFP is favorable for liquid-metal cooling. The first wall and blanket consist of single pass poloidal-flow loops aligned with the dominant poloidal magnetic field. A unique feature of the TITAN-I design is the use of the integrated-blanket-coil (IBC) concept. The lithium coolant in the blanket circuit is also used as the electrical conductor of the toroidal-field and divertor coils. A “single-piece” FPC maintenance procedure is used, in which the first wall and blanket are removed and replaced by vertical lift of the components as a single unit. This unique approach permits the complete FPC to be made of a few factory-fabricated pieces, assembled on site into a single torus, and tested to full operational conditions before installation in the reactor vault. A low-activation, low-afterheat vanadium alloy is used as the structural material throughout the FPC in order to minimize the peak temperature during accidents and to permit near-surface disposal of waste. The safety analysis indicates that the liquid-metal-cooled TITAN-I design can be classified as passively safe, without reliance on any active safety systems. The results from the TITAN study support the technical feasibility, economic incentive, and operational attractiveness of compact, high-MPD RFP reactors. Many critical issues remain to be resolved, however. The physics of confinement scaling, plasma transport and the role of the conducting shell are already major efforts in RFP research. However, the TITAN study points to three other major issues. First, operating high-power-density fusion reactors with intensely radiating plasmas is crucial. Second, the physics of toroidal-field divertors in RFPs must be examined. Third current drive by magnetic-helicity injection must be verified. The key engineering issues for the TITAN I FPC have also been defined. Future research and development will be required to meet the physics and technology requirements that are necessary for the realization of the significant potential economic and operational benefits that are possible with TITAN-like RFP reactors.

Conceptual design of a moving-ring reactor

A design of a prototype moving-ring reactor was completed, and a development plan for a pilot reactor is outlined. The fusion fuel is confined in current-carrying rings of magnetically field-reversed plasma (compact toroids). The plasma rings, formed by a coaxial plasma gun, undergo adiabatic magnetic compression to ignition temperature while they are being injected into the reactors burner section. The cylindrical burner chamber is divided into three burn stations. Separator coils and a slight axial guide field gradient are used to shuttle the ignited toroids rapidly from one burn station to the next, pausing for one-third of the total burn time at each station. Deuterium-tritium-/sup 3/He ice pellets refuel the rings at a rate that maintains constant radiated power. The fusion power per ring is approx. =105.5 MW. The burn time to reach a fusion energy gain of Q = 30 is 5.9 s.

Low activation fusion reactor design studies

A design study for a low activation tokamak fusion reactor based on the STARFIRE baseline design has been done. The major components of limiter, first wall, blanket, shield and toroidal field coils have all been designed with very low activation materials and the designs appear technically achievable. The result provides a fusion power reactor with a high degree of direct personnel access for maintenance and repair, with a large reduction in safety and environmental impact, and with much reduced waste disposal problems. This low activation design also appears economically attractive and is expected to have a high degree of public acceptance.