D. Steiner

Overview of the ARIES-RS reversed-shear tokamak power plant study

The ARIES-RS tokamak is a conceptual, D‐T-burning 1000 MWe power plant. As with earlier ARIES design studies, the final design of ARIES-RS was obtained in a self-consistent manner using the best available physics and engineering models. Detailed analyses of individual systems together with system interfaces and interactions were incorporated into the ARIES systems code in order to assure self-consistency and to optimize towards the lowest cost system. The ARIES-RS design operates with a reversed-shear plasma and employs a moderate aspect ratio (A4.0). The plasma current is relatively low (Ip11.32 MA) and bootstrap current fraction is high ( fBC 0.88). Consequently, the auxiliary power required for RF current drive is relatively low ( 80 MW). At the same time, the average

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.

Neutron irradiation effects on the density, tensile properties and microstructural changes in Hi-Nicalon™ and Sylramic™ SiC fibers

Abstract Tensile results are presented for ceramic grade (cg) Nicalon™, Hi-Nicalon™ and Sylramic™ SiC fibers which have all been neutron irradiated in the high flux isotope reactor (HFIR) at damage levels of 0.1, 0.5, 2 and 5 dpa. Single fibers were tensile tested and the results were analyzed using Weibull statistics. Fiber axial displacements were measured with a laser micrometer which allowed for the determination of the tensile moduli. Density changes were measured with a gradient column. Transmission electron microscopy (TEM) was performed to assess microstructural damage and X-ray diffraction (XRD) was used to measure uniform strain, degree of crystallinity, average coherence length and root-mean-square microstrain. The physical and tensile results indicate that cg Nicalon™ and Hi-Nicalon™ are unstable in a neutron field. Both fiber types densify by 3–5% which would be detrimental to a composites matrix cracking stress due to weakening or debonding of the interface. The Sylramic™ swells which is similar behavior to the monolithic SiC. The failure strength of the Sylramic™ drops by 50% after an irradiation temperature of 500°C which would have little effect on the matrix cracking condition of a composite. The Sylramic™ fiber strength decrease would significantly reduce the ultimate composite strength but the composite strength would remain above the matrix cracking strength such that the fibers may still potentially be viable for fusion applications.

Radiation induced microstructure and mechanical property evolution of SiC/C/SiC composite materials

Chemically vapor deposited (CVD) SiC/C/Nicalon composites have been neutron irradiated in both HFIR and FFTF from 1 to 15 dpa and have been ion beam damaged with 3 MeV carbon ions to 30 dpa in a temperature range from room temperature to 900°C. Following room temperature carbon irradiation amorphization occurred in both the CVD SiC and Nicalon fiber with measured amorphization thresholds of 15 and 1 dpa, respectively. Elastic modulus and hardness have been measured for both the ion beam and neutron irradiated materials. The CVD SiC showed a significant decrease in modulus and hardness following irradiation while the Nicalon fibers modulus and hardness increased.

AN EVALUATION OF FUSION ENERGY R&D GAPS USING TECHNOLOGY READINESS LEVELS

Abstract The ARIES Team currently is engaged in an effort called the “ARIES Pathways Study”. The goals of this study are to evaluate remaining R&D needs toward practical fusion energy and to identify and evaluate possible “next step” devices to bridge the gap between ITER and an attractive power plant. In order to evaluate our current state of readiness and remaining R&D needs, we adopted a methodology called “Technology Readiness Levels”. We defined a quantitative set of readiness levels that encompass the major technology challenges for fusion energy development, and have applied them to evaluate our current level of advancement and R&D needs for an advanced tokamak power plant concept based on recent ARIES designs. Results of the evaluation and recommendations for future R&D are presented.

Applications of the Aqueous Self-Cooled Blanket concept

In this paper a novel water-cooled blanket concept is examined. This concept, designated the Aqueous Self-Cooled Blanket (ASCB), employs water with small amounts of dissolved fertile compounds as both the coolant and the breeding medium. The ASCB concept is reviewed and its application in three different contexts is examined: (1) power reactors; (2) near-term devices such as NET; and (3) fusion-fission hybrids.

The ARIES-III D-3He tokamak-reactor study

A description of the ARIES-III research effort is presented, and the general features of the ARIES-III reactor are described. The plasma engineering and fusion-power-core design are summarized, including the major results, the key technical issues, and the central conclusions. Analyses have shown that the plasma power-balance window for D-/sup 3/He tokamak reactors is small and requires a first wall (or coating) that is highly reflective to synchrotron radiation and small values of tau /sub ash// epsilon /sub e/ (the ratio of ash-particle to energy confinement times in the core plasma). Both first and second stability regimes of operation have been considered. The second stability regime is chosen for the ARIES-III design point because the reactor can operate at a higher value of tau /sub ash// tau /sub E// tau /sub E/ approximately=2 (twice that of a first stability version), and because it has a reduced plasma current (30 MA), magnetic field at the coil (14 T), mass, and cost (also compared to a first-stability D-/sup 3/He reactor). The major and minor radii are, respectively 7.5 and 2.5 m.<<ETX>>

The integrated-blanket-coil concept applied to the poloidal field and blanket systems of a tokamak reactor

A novel concept is proposed for combining the blanket and coil functions of a fusion reactor into a single component. This concept, designated the integrated-blanket-coil (IBC) concept, is applied to the poloidal field and blanket systems of a Tokamak reactor. An examination of resistive power losses in the IBC suggests that these losses can be limited to less than or equal to 10% of the fusion thermal power. By assuming a sandwich construction for the IBC walls, MHD-induced pressure drops and associated pressure stresses are shown to be modest and well below design limits. For the stainless steel reference case examined in this paper, the MHD-induced pressure drop was estimated to be approx. 1/3 MPa and the associated primary membrane stress was estimated to be approx. 47 MPa. The preliminary analyses presented in this paper indicate that the IBC concept offers promise as a means for making fusion reactors more compact by combining blanket and coils functions in a single component.

Tensile behavior of irradiated SiC fibers

Abstract The strength and toughness of continuous fiber reinforced ceramic composites (CFCCs) are highly dependent on the fiber strength distribution. To first order, weaker fibers lead to low strength but higher toughness while stronger fibers lead to high strength composites of relatively low toughness. Toughness is associated with pullout of the fibers from the ceramic matrix. It has been shown previously that both strength and toughness of SiC/Nicalon TM composites are drastically changed following irradiation. Tensile results are presented for low oxygen Nicalon fibers neutron irradiated at damage levels of 0.013 displacements per atom (dpa), 0.13 dpa and 0.32 dpa. Single fibers were tensile tested and analyzed, using Weibull statistics, for mean strength and distribution. Tensile modulus was also determined. Using a diffractometer, the fiber grain size and percent crystallinity were determined. The initial results of these low fluence neutron irradiations exhibit no substantial degradation of the properties investigated. Therefore, continued research at higher doses is recommended.

Improved elastic collision modeling in DEGAS 2 for low-temperature plasmas

Recent emphasis on low-temperature divertor operations has focused attention on proper treatment of neutral-elastic collisions in low-temperature environments. For like species collisions, as in D++D, quantum mechanical indistinguishability precludes differentiation of small-angle elastic scattering from resonant charge exchange for collision energies <2 eV. The current work improves the low-temperature simulation capabilities of the DEGAS 2 Monte Carlo neutral transport code [D. P. Stotler and C. F. F. Karney, Contrib. Plasma Phys. 34, 392–397 (1994)] by employing a set of quantum mechanical collision cross sections produced by Oak Ridge National Laboratory to provide a comprehensive treatment of ion-neutral elastic collisions. Ion-molecular collisions in the form of D++D2 are included for the first time. An integration technique is utilized that reduces the total collision cross section while keeping the other transport cross sections invariant. The inclusion of ion-molecular elastic collisions results ...