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Fusion alpha heating introduces new phenomena into plasma dynamics and control. On the worrisome side is the well-known fact that the συfus≃Tion2 dependence of the predominantly central fusion heat...

The relationships among the radial distributions of neutral beam momentum and particle sources, the radial distribution of ion orbit losses, and the resulting radial distributions of toroidal and p...

A particle-, momentum-, and energy-conserving, flux surface–averaged fluid theory for the radial particle and energy fluxes and the radial distributions of pressure, density, rotation velocities, and temperatures in the edge plasma that has been derived from fundamental fluid conservation (particle, momentum, energy) relations is summarized. Kinetic corrections arising from ion orbit loss are incorporated into the fluid equations, which are integrated to determine the dependence of the observed edge pedestal profile structure on fueling, heating, electromagnetic, and thermodynamic forces. Solution procedures for the fluid plasma and associated neutral transport equations are discussed.

This paper combines the older neoclassical gyroviscous model for toroidal viscosity in the plasma core, which is based on an axisymmetric magnetic field and obtains reasonable agreement with experiment for toroidal rotation in the plasma core but not in edge plasma, with recent models for neoclassical toroidal viscosity (NTV) based on nonaxisymmetric “perturbation” magnetic field components present primarily in the edge plasma to obtain a composite toroidal viscosity model for toroidal velocity calculations in the tokamak core and edge plasma. This combination is facilitated by the fact that the same form of “drag frequency” representation of the viscous torque used in many of the new (NTV) torque models arising from toroidally nonaxisymmetric perturbation magnetic fields that are present mostly in the plasma edge can also be used to represent the old neoclassical toroidal viscous torques arising from toroidally axisymmetric magnetic fields.

Theoretical analysis and interpretation of experimental measurements indicate the need to extend the fluid theory used in the tokamak plasma edge to include ion orbit loss of thermalized ions and to retain (mainly) electromagnetic pinch forces in the momentum balance in order to derive transport equations which conserve particles, energy, and momentum. The features of such an extended steady-state fluid theory have been derived from first principles in several papers and are summarized herein.

A customized dynamic safety model is developed and used to analyze the safety characteristics of the Subcritical Advanced Burner Reactor (SABR), a fast transmutation reactor driven by a tokamak fus...

The Georgia Tech concept of the Subcritical Advanced Burner Reactor (SABR) spent nuclear fuel (SNF) transmutation reactor and supporting analyses to date are summarized. SABR is based on the fast reactor physics and technology prototyped in Experimental Breeder Reactor-II (EBR-II) and proposed for the Integral Fast Reactor and the PRISM Reactor and on the tokamak fusion neutron source physics and technology that will be prototyped in ITER. Preliminary fuel cycle calculations indicate that subcritical operation would enable a proliferation-resistant fuel reprocessing cycle that would safely accommodate fuel with up to 100% TRU content and that introduction of SABRs in a 1-to-3 power ratio with light water reactors would reduce the required SNF high-level waste repository capacity (defined on the basis of decay heat released) by a factor of 10 to 100. Preliminary dynamic safety calculations indicate that SABRs could be shut down to the decay heat level by turning off the plasma heating power without...

Investigations of tokamak dynamics, especially as they relate to the challenge of burn control, require an accurate representation of energy and particle confinement times. While the ITER-98 scalin...

The realities of energy development and the perception of and support for magnetic fusion in the US are briefly summarized as background for proposing a strategic opportunity for magnet fusion energy development as fusion neutron sources for subcritical advanced burner (transmutation) reactors for the destruction of long-lived transuranics in spent nuclear fuel.

The subcritical advanced burner reactor (SABR) concept, which combines IFR-PRISM fast reactor technology and the ITER tokamak fusion physics and technology in a burner reactor for the transmutation...

The conceptual design of the subcritical advanced burner reactor (SABR), a 3000-MW(thermal) annular, modular sodium pool–type fast reactor, fueled by metallic transuranic (TRU) fuel process...

It is argued that the structure observed in radial profiles in the tokamak edge plasma is determined by the requirements of ion particle, momentum and energy conservation and the underlying transport mechanisms in the presence of sources and losses of particles, energy and momentum. The intent of this paper is to define a systematic formalism that can be employed for evaluating these transport coefficients from experimental inference and comparison with theory. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GTROTA (Georgia Tech ROTAtion) is a code that solves the extended neoclassical rotation equations for tokamak plasmas, derived from the multifluid moment equations (including electromagnetic effects) in generalized toroidal magnetic flux surface geometry. It computes the toroidal and poloidal fluid rotation velocities and the in–out and up–down density asymmetries at each radial location. The solution of these equations is accomplished iteratively, using a physically motivated decomposition, successive over-relaxation and the concept of simulated annealing. Program summary Program title: GTROTAv1 Catalogue identifier: AEPT_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEPT_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 12 890 No. of bytes in distributed program, including test data, etc.: 1 099 937 Distribution format: tar.gz Programming language: Matlab. Computer: Any workstation or PC where Matlab can be run. Operating system: Any with Matlab available. Tested on Windows 7. RAM: 1024 MB to run Matlab Classification: 19.11. Nature of problem: Tokamak plasma rotation velocities and the poloidal in–out and up–down asymmetries of plasma densities are calculated from the coupled set of nonlinear equations, which show a very instable iterative dynamics. To solve for the true solution for this nonlinearly coupled system that does not converge to a single solution, physics-based determination of the true solution becomes necessary and GTROTA provides the algorithm for users to find the true solution from the nonlinear topological maps. Solution method: The code decomposes the given system into three subsystems to stabilize the iterative dynamics and uses Successive Over-Relaxation and the concept of Simulated Annealing to determine the true solution. Restrictions: The code is designed for strong rotation analysis. An updated code for slow rotation and plasma edge analysis is to be developed in the future. Unusual features: For a new rotation calculation, the code requires several test runs to determine the iterations step for the true solution. Additional comments: Due to the extreme nonlinearity of the extended rotation calculation model, the signs of the inputs must be adjusted correctly to yield correct solutions. Refer to the User’s Manual for this discussion. Running time: 8 s (except test runs that depend on the complexity of the nonlinear dynamics).

The dependence of the kinetic ion orbit loss of thermalized ions in a tokamak plasma on the charge and mass of these ions is explicitly developed from the underlying ion orbit loss theory.The dependence of the kinetic ion orbit loss of thermalized ions in a tokamak plasma on the charge and mass of these ions is explicitly developed from the underlying ion orbit loss theory.

Fuel cycle analyses of the transmutation of (a) all of the transuranics (TRUs) in light water reactor (LWR) spent nuclear fuel (SNF) and of (b) the minor actinides (MAs) remaining in SNF (after separation of much of the plutonium for starting up fast reactors) have been performed for the conceptual subcritical advanced burner reactor (SABR) fission-fusion hybrid sodium-cooled fast burner reactor. Both metallic and oxide burner reactor fuels were considered, and the effect of clad radiation damage limit on fuel residence time was investigated. For a radiation damage limit of 200 displacements per atom, the support ratio (LWR power/SABR power) for transmuting all of the TRUs produced by LWRs is 3/1, and for transmuting just the MAs produced by LWRs the support ratio is 25/1. The reduction in high-level waste repository capacity required due to this transmutation is a factor of 10, based on a decay heat at a 100000-yr limit on capacity.

The presence of a large pinch velocity in the edge pedestal of high-confinement (H-mode) tokamak plasmas implies that particle transport in the plasma edge must be treated by a generalized pinch-diffusion theory, rather than a pure diffusion theory. An investigation of extending the numerical solution methodology of the standard diffusion theory to the solution of the generalized pinch-diffusion theory has been carried out. It is found that in the edge pedestal, where the inward pinch velocity is large in H-mode plasmas, a finer mesh spacing will be required than is necessary for similar accuracy farther inward, where the pinch velocity diminishes. An expression for the numerical error in various finite-differencing algorithms is presented.

The transient response of the subcritical advanced burner reactor (SABR) subcritical, sodium-cooled, transuranic fueled, fast transmutation reactor design concept, which ensued from several accident initiation events, has been simulated. The results establish such things as the number of primary loop pumps that could fail or the magnitude of flow reduction in the intermediate loop heat removal capability due to either pump failure or intermediate heat exchange failure that could be tolerated without core damage, the consequences of loss of electrical power, and the consequences of control rod ejection or neutron source excursions. Suggestions are offered for design changes to improve the already good safety characteristics of the design concept.

An extended plasma fluid theory including atomic physics, radiation, electromagnetic and themodynamic forces, external sources of particles, momentum and energy, and kinetic ion orbit loss is employed to derive theoretical expressions that display the role of the various factors involved in the determination of the pressure and temperature gradients in the edge of tokamak plasmas. Calculations for current experiments are presented to illustrate the magnitudes of various effects including strong radiative and atomic physics edge cooling effects and strong reduction in ion particle and energy fluxes due to ion orbit loss in the plasma edge. An important new insight is the strong relation between rotation and the edge pressure gradient.

The possibility that a tokamak D-T fusion neutron source, based on ITER physics and technology, could be used to drive sub-critical, fast-spectrum nuclear reactors fueled with the transuranics (TRU) in spent nuclear fuel discharged from conventional nuclear reactors has been investigated at Georgia Tech in a series of studies which are summarized in this paper. It is found that sub-critical operation of such fast transmutation reactors is advantageous in allowing longer fuel residence time, hence greater TRU burnup between fuel reprocessing stages, and in allowing higher TRU loading without compromising safety, relative to what could be achieved in a similar critical transmutation reactor. The required plasma and fusion technology operating parameter range of the fusion neutron source is generally within the anticipated operational range of ITER. The implications of these results for fusion development policy, if they hold up under more extensive and detailed analysis, is that a D-T fusion tokamak neutron source for a sub-critical transmutation reactor, built on the basis of the ITER operating experience, could possibly be a logical next step after ITER on the path to fusion electrical power reactors. At the same time, such an application would allow fusion to contribute to meeting the nation’s energy needs at an earlier stage by helping to close the fission reactor nuclear fuel cycle.

The design concept of a subcritical advanced burner reactor (SABR) is described. SABR is fueled with transuranics (TRUs) discharged from thermal reactors cast into a TRU-Zr metal fuel pin and is cooled with sodium. The reactor operates subcritical to achieve a deep-burn four-batch fuel cycle that fissions 25% of the TRU in an 8.2-yr residence time, limited by radiation damage accumulation (200 displacements per atom) in the oxygen dispersion strengthened clad and structure. The annual TRU fission rate in SABR [3000 MW(thermal)] is comparable to the annual TRU discharge of three to five 1000-MW(electric) light water reactors, depending on the plant capacity factor of SABR. A tokamak D-T fusion neutron source based on physics and technology that will be demonstrated in ITER supports the subcritical operation.

Predictions of the recently developed paleoclassical transport model are compared with data from many toroidal plasma experiments: electron heat diffusivity in DIII-D, C-Mod and NSTX ohmic and near-ohmic plasmas; transport modeling of DIII-D ohmic-level discharges and of the RTP ECH 'stair-step' experiments with eITBs at low order rational surfaces; investigation of a strong eITB in JT-60U; H-mode Te edge pedestal properties in DIII-D; and electron heat diffusivities in non-tokamak experiments (NSTX/ST, MST/RFP, SSPX/spheromak). The radial electron heat transport predicted by the paleoclassical model is found to agree with a wide variety of ohmic-level experimental results and to set the lower limit (within a factor {approx} 2) for the radial electron heat transport in most resistive, current-carrying toroidal plasmas -- unless it is exceeded by fluctuation-induced transport, which often occurs in the edge of L-mode plasmas and when the electron temperature is high ({approx}>T{sub e}{sup crit} {approx}B{sup 2/3}{bar {alpha}}{sup 1/2} keV) because then paleoclassical transport becomes less than gyro-Bohm-level anomalous transport.

A conceptual design has been developed for a tokamak D-T fusion neutron source, based on ITER physics and technology, for a sub-critical fast reactor that would transmute the fissionable transuranic isotopes in spent nuclear fuel.

A series of design scoping and fuel cycle studies for sub-critical fast transmutation reactors driven by tokamak fusion neutron sources has been carried out to determine if the requirements on the tokamak neutron sources are compatible with the fusion physics and technology design database that will exist after the operation of ITER and to determine if there is a significant advantage in fuel cycle flexibility due to sub-critical operation that would justify the additional cost and complexity of a fusion neutron source. The fast reactor technologies are based on reactor concepts being developed in the DoE Generation-IV and Advanced Fuel Cycle initiatives.

The strong temperature dependence, over certain temperature ranges, of the radiation cooling rate of low-Z impurities, of the atomic physics cooling and particle source rates associated with recycl...

Geologic repositories for the long-term storage of spent nuclear fuel (SNF) are limited in their capacity by the amount of decay heat emitted by the SNF. The largest long-term contribution to this decay heat comes from the transuranics (TRUs), the destruction of which could increase storage capacity by a factor of at least 10. A design concept for a subcritical gas-cooled fast transmutation reactor (GCFTR) fueled with TRUs from SNF is being developed. This paper presents the results of analyses of several GCFTR fuel cycle scenarios that have a deep-burn (>90% burnup of the TRU fuel) primary objective and a secondary objective of avoiding reprocessing of the TRU fuel if possible.

This paper summarizes a series of conceptual design studies conducted with the purpose of determining if tokamak fusion neutron sources based on ITER physics and technology could meet the neutron source requirements for sub-critical fast-spectrum nuclear reactors that would help to close the nuclear fuel cycle by transmuting the transuranics in spent nuclear fuel. The studies were constrained to nuclear reactor and materials technologies under consideration in the US nuclear programme. Fuel cycle studies indicate that fusion neutron sources in the range ~200–500 MW would meet the needs of transmutation reactors, depending on other constraints such as materials damage to the nuclear fuel. A tokamak with R = 3.75 m, a = 1.1 m, B = 5.7–5.9 T, q95 = 3.00–4.0, I = 8.3–10 MA, βN = 2.0–2.85, HIPB98 = 1.0–1.06, γcd = 0.6 A Wm−2 would meet these requirements.

There are a number of potential neutron transmutation missions (destruction of long-lived radioisotopes in spent nuclear fuel, ‘disposal’ of surplus weapons-grade plutonium, ‘breeding’ of fissile nuclear fuel) that perhaps best can be performed in sub-critical nuclear reactors driven by a neutron source. The requirements on a tokamak fusion neutron source for such transmutation missions are significantly less demanding than for commercial electrical power production. A tokamak fusion neutron source based on the current physics and technology database (ITER design base) would meet the needs of the spent nuclear fuel transmutation mission; the technical issue would be achieving ≥50% availability, which would require advances in component reliability and in steady-state physics operation.

Reprinted by permission of Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim: http://www.interscience.wiley.com

The principal results of a series of design scoping studies of sub-critical fast transmutation reactors (based on the nuclear and processing technology being developed in the USDoE Generation IV, Advanced Fuel Cycle and Next Generation Nuclear Plant programs) coupled with a tokamak fusion neutron source (based on the ITER design basis physics and technology) are presented.

The hypothesis is advanced and it is investigated that, in between or in the absence of edge-localized modes, the structure of the edge pedestal is determined by the transport requirements of plasma particle, momentum and energy balance, and by recycling neutral atoms. A set of “pedestal equations” following from this hypothesis are presented and applied to calculate the edge density, temperature, rotation velocity, and radial electric field profiles in a DIII-D H (high)-mode plasma. It is found that a pedestal structure in the density profile and sharp negative peaks in the radial electric field and poloidal velocity just inside the separatrix are predicted as natural consequences of the conservation of particle and momentum, in qualitative and quantitative agreement with measured values. Detailed examination of the calculation reveals a sequence of mechanisms by which the ionization of recycling neutrals affect the structure of the density profile in the edge pedestal.

A “first-principles” model for the structure of the edge density pedestal in tokamaks between or in the absence of edge localized magnetohydrodynamic instabilities is derived from ion momentum and particle conservation and from the transport theory of recycling neutral atoms. A calculation for (high) H-mode tokamak discharge parameters indicates that the equations have a self-consistent solution which has an edge pedestal in the ion density profile and sharp negative spikes in the poloidal velocity and radial electric field profiles in the edge pedestal, features characteristic of H-mode edge profiles. These sharp negative spikes in radial electric field and poloidal rotation produce a peak in the inward ion pinch velocity in the sharp gradient (pedestal) region which produces an edge particle transport barrier. The calculated magnitude of the density at the top of the pedestal and the density gradient scale length and radial electric field in the pedestal region are comparable to measured values.

A model for the calculation of toroidal rotation velocities and the radial electric field in the edge pedestal of tokamaks is described. The model is based on particle and momentum balance and the use of the neoclassical gyroviscous expression for the toroidal viscous force. Predicted toroidal rotation velocities in the edge pedestal are found to agree with measured values to within about a factor of 2 or less, for a range of DIII-D [Luxon, Nucl. Fusion 42, 614 (2002)] edge pedestal conditions.

A new flux-gradient relation for the ion particle flux in the edge pedestal is derived from continuity and momentum balance, taking into account atomic physics, and cast in the form of a generalized 'diffusion-pinch' transport relation. This flux-gradient relation is used to derive a new expression for a first-principles calculation of the ion density gradient scale length.

A comparison of various heat conduction theories with data from several DIII-D [Luxon, Nucl. Fusion 42, 614 (2002)] shots indicates: (1) that neoclassical theory is in somewhat better agreement with experiment than is ion temperature gradient mode theory for the ion thermal conductivity in the edge pedestal, although both are in reasonable agreement with experiment for most discharges; and (2) that electron temperature gradient theory (k⊥cs⩽ωpe) is in much better agreement with experiment than is electron drift wave theory (k⊥cs⩽Ωi) for the electron thermal conductivity. New theoretical expressions derived from momentum balance are presented for: (1) a “diffusive-pinch” particle flux, (2) an experimental determination of the momentum transfer frequency, and (3) the density gradient scale length. Neither atomic physics nor convection can account for the measured momentum transfer frequencies, but neoclassical gyroviscosity predictions are of the correct magnitude.

Recent extensions of the Transmission and Escape Probability methodology and its implementation in the 2-D neutral transport code GTNEUT are presented. These extensions address the issues of anisotropy of the neutral distribution function at the interfaces and the non-uniformity of the first collision source in short mean free path regions. Comparisons with Monte Carlo for a number of model problems are discussed. The Transmission and Escape Probability (TEP) interface current balance method (1) has been developed and implemented into the 2-D neutral transport code GTNEUT to provide a fast and accurate calculation of neu- tral particle transport in the complex tokamak edge and divertor configuration. Tests of GTNEUT predictions against Monte Carlo calculations and experimental measurements in DIII-D have demonstrated (2-5) the accu- racy and computational efficiency of the TEP method for a wide range of conditions. However, calculations of detailed model problems (3,4) designed to test approximations in limiting cases have identified two main areas in which extensions in the original TEP methodology would be useful: 1) taking anisotropy into account in the calculation of first-flight transmission coefficients when the neutral mean free path (mfp) is much larger than the characteristic dimension of the computational region; and 2) taking into account that the escape of scattered or charge-exchanged neutrals is preferentially across the incident surface when the mfp is small compared to the characteristic dimension of the computational region. In this paper, we discuss recent extensions of the TEP methodology which address the above issues. The anisotropy of the neutral distribution function at the interfaces is taken into account by implementing Double P1 (DP1) and Double P2 (DP2) approximations. The preferential backscattering of scattered or charge-exchange neutrals across the incident surface is addressed by implement- ing an albedo-based condition to describe the fraction of the collided neutrals that are reflected back across the incident surface.

A test of a new model for the low-to-high (L–H) mode power threshold, based on the stabilization of edge thermal instabilities, is made by comparison with a set of DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] discharges at times just prior to a L–H transition. Agreement is found between the measured power crossing the separatrix just prior to the L–H transition and the predicted power threshold for the stabilization of transport enhancing thermal instabilities.

We are developing a Fusion Transmutation of Waste Reactor (FTWR) concept—a subcritical, metal fuel, liquid metal cooled fast reactor driven by a tokamak DT fusion neutron source. An emphasis is placed on using nuclear, separation/processing and fusion technologies that either exist or are at an advanced state of development and on using plasma physics parameters that are supported by the existing database. We have previously discussed the general capabilities of DT tokamak neutron sources for driving transmutation reactors [1] and developed a design concept for a FTWR [2] based on normal conducting magnets. The concept has been further developed in papers dealing with nuclear design and safety [3] and with the evaluation of the potential impact on radioactive waste management [4]. The purpose of this paper is to examine how the FTWR design concept would change if superconducting magnets were used.

The nuclear design and safety analyses for the Fusion Transmutation of Waste Reactor (FTWR) are described. The advantages of sub-critical operation for nuclear stability and safety are illustrated.