Rodger C. Martin

The ARIES-I Tokamak Reactor Study †

The ARIES research program is a multi-institutional effort to develop several visions of tokamak reactors with enhanced economic, safety, and environmental features. Three ARIES visions are currently planned for the ARIES program. The ARIES-I design is a DT-burning reactor based on modest extrapolation from the present tokamak physics data base; ARIES-II is a DT-burning reactor which will employ potential advances in physics; and ARIES-III is a conceptual D-3He reactor. The first design to be completed is ARIES-I, a 1000 MWe power reactor. The key features of ARIES-I are: (1) a passively safe and low environmental impact design because of choice of low activation material throughout the fusion power core, (2) an acceptable cost of electricity, (3) a plasma with performance as close as possible to present-day experimental achievements, (4) a high performance, low activation, SiC composite blanket cooled by He, and (5) an advanced Rankine power cycle as planned for near term coal-fired plants. The ARIES-I research has also identified key physics and technology areas with the highest leverage for achieving attractive fusion power system.

The ARIES tokamak fusion reactor study

The Advanced Reactor Innovation and Evaluation Study (ARIES) is a community effort to develop several visions of the tokamak as a fusion power reactor. The aims are to determine its potential economics, safety, and environmental features and to identify physics and technology areas with the highest leverage for achieving the best tokamak reactor. The authors focus on the ARIES-1 design. Parametric systems studies show that the optimum first stability tokamak has relatively low plasma current ( approximately 12 MA), high plasma aspect ratio ( approximately 4-6), and high magnetic field ( approximately 24 T at the coil). ARIES-I is a 1000-MWe (net) reactor with a plasma major radius of 6.5 m, a minor radius of 1.4 m, a neutron wall loading of about 2.8 MW/m/sup 2/, and a mass power density of about 90 kWe/tonne. The ARIES-I reactor operates at steady state using ICRF (ion-cyclotron range of frequency) fast waves to drive current in the plasma core and lower-hybrid waves for edge-plasma current drive. The ARIES-I blanket is cooled by He and consists of SiC-composite structural material, Li/sub 4/SiO/sub 4/ solid breeder, and Be neutron multiplier, all chosen for their low-activation and low-decay after-heat in order to enhance the safety and environmental features of the design. The ARIES-I design has a competitive cost of electricity and superior safety and environmental features.<<ETX>>

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 V3TiISi and V15Cr5Ti 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 V3Ti1Si. Coolant compatibility issues are investigated. The liquid lithium compatibility of the two vanadium alloys, V15Cr5Ti and V3Ti1Si, 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 ).

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>>

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.

Overview of the TITAN-I fusion-power core

The TITAN reactor is a compact (major radius of 3.9 m and plasma minor radius of 0.6 m), high neutron wall loading (~18 MW/m 2 ) fusion energy system based on the reversed-field pinch (RFP) confinement concept. The reactor thermal power is 2918 MWt resulting in net electric output of 960 MWe and a mass power density of 700 kWe/tonne. The TITAN-I fusion power core (FPC) is a lithium, self-cooled design with vanadium alloy (V-3Ti-1Si) structural material. The surface heat flux incident on the first wall is ~4.5 MW/m 2 . The magnetic field topology of the RFP is favorable for liquid metal cooling. In the TITAN-I design, 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. With the IBC concept the poloidal flow lithium circuit is also the electrical conductor of the toroidal-field and divertor coils. Three dimensional neutronics analysis yields a tritium breeding ratio of 1.18 and a molten salt extraction technique is employed for the tritium extraction system. Almost every FPC component would qualify for Class C waste disposal. The compactness of the design allows the use of single-piece maintenance of the FPC. This maintenance procedure is expected to increase the plant availability. The entire FPC operates inside a vacuum tank, which is surrounded by an atmosphere of inert argon gas to impede the flow of air in the system in case of an accident. The top-side coolant supply and return virtually eliminate the possibility of a complete LOCA occurring in the FPC. The peak temperature during a LOFA is 991 °C.

Properties of concentrated aqueous lithium nitrate solutions and applications to fusion reactor design

Aqueous solutions of Li-containing compounds have been proposed to serve as the combined tritium breeding material and coolant for fusion reactors. The salt used for the TITAN-II reversed-field-pinch reactor design is LiNO3, which was chosen for its good neutronics properties, relatively good corrosion characteristics, and for its high solubility in water. An extensive literature survey has shown that the physical and thermal properties of high-temperature, concentrated aqueous LiNO3 solutions are markedly different from the pure water properties at similar conditions. These changes alter the heat transfer performance of the coolant, and the critical heat flux is estimated to rise for sub-cooled flow boiling, while the heat transfer coefficient for forced convection falls. Another important result is the elevation in boiling point, which may allow the operating pressure of the primary coolant to be reduced to a value below that of the secondary steam circuit, preventing leakage of the tritiated coolant into the steam circuit. Further research is needed into corrosion and radiolysis issues, but the available data imply that careful control of the coolant chemistry can minimize the problems.

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.

Materials selection criteria and performance analysis for the TITAN-II reversed-field-pinch fusion power core

Abstract The TITAN-II reactor is a compact, high-neutron-wall-loading (18 MW/m2) design. The TITAN-II fusion power core (FPC) is cooled by an aqueous lithium-salt solution that also acts as the breeder material. The use of an aqueous solution imposes special constraints on the selection of structural and breeder material because of corrosion concerns, hydrogen embrittlement, and radiolytic effects. In this paper, the materials engineering and design considerations for the TITAN-II FPC are presented. Material selection criteria, based on electrochemical corrosion mechanisms of aqueous solutions coupled with radiolysis of water by ionizing radiation, resulted in the choice of a low-activation ferritic steel as structural material for TITAN-II. Stress corrosion cracking, hydrogen embrittlement, and changes in the ductile-to-brittle transition temperature of ferritic alloys are discussed. Lithium-nitrate (LiNO3) salt was chosen over lithium hydroxide (LiOH) because it is less corrosive and reduces the net radiolytic decomposition rate of the water. The dissolved salt in the coolant changes the thermophysical properties of the coolant results in trade-offs between the lithium concentration in the coolant, neutronics performance, thermal and structural design. The TITAN-II design requires a neutron multiplier to achieve an adequate tritium breeding ratio. Beryllium is the primary neutron multiplier, assuming a maximum swelling of about 10% based on continuous self-limiting microcracking/sintering cycles.

Modeling of tritium transport in a fusion reactor pin-type solid breeder blanket using the diffuse code

A pin-type fusion reactor blanket is designed using γ -LiAlO 2 solid tritium breeder. Tritium transport and diffusive inventory are modeled using the DIFFUSE code. Two approaches are used to obtain characteristic LiAlO 2 grain temperatures. DIFFUSE provides intragranular diffusive inventories which scale up to blanket size. These results compare well with a numerical analysis, giving a steady-state blanket tritium inventory of 13 g. Start-up transient inventories are modeled using DIFFUSE for both full and restricted coolant flow. Full flow gives rapid inventory buildup while restricted flow prevents this buildup. Inventories after shutdown are modeled: reduced cooling is found to have little effect on removing tritium, but preheating rapidly purges inventory. DIFFUSE provides parametric modeling of solid breeder density, radiation, and surface effects. 100% dense pins are found to give massive inventory and marginal tritium release. Only large trapping energies and concentrations significantly increase inventory. Diatomic surface recombination is only significant at high temperatures.