SBIR-STTR Award

More than three decades have passed since the United States embarked on a program to develop fusion energy. Since 1973, numerous systems studies have produced conceptual fusion reactor designs that have not been viewed as meeting the needs of electric utilities. These studies have featured superconducting confinement tokamaks and mirrors because of the greater understanding of their physics basis and the conviction that superconducting magnets offered the only hope for an acceptable power balance. However, other design efforts have included a variety of confinement concepts based on normally conducting magnets. These studies indicate that this magnet approach can be economically attractive providing that high gain is achieved, subject to first wall heat flux constraints, and that neutron dose to the reactor internals is recognized as a limit. The proposed work is based on a tokamak concept that has been conceived subject to the above conditions. It is directed at high field operation to compensate for modest beta performance, high gain, and a reactor maintenance configuration for the changeout of neutrondamaged cores. Called the Demountable Tokamak Fusion Core (DTFC) concept, it provides for the replacement of the center portion of the tokamak, including the inner toroidal field coil assembly, the OH/PF coils, and the First Wall assembly. The outer TF coil assembly and the main blanket are only infrequently replaced. This scenario is consistent with the fact that reactor internals are replaced when a target amount of energy has been delivered (at a given neutron dose.) Phase I of the proposed work is directed at key technological features of the DTFC; specifically upgrading the reactor performance model, confirming the nuclear performance, analyzing the TF coil joint and analyzing the inner TF coil-OH interface.AnticipatedResults Potential Commercial Applications as described by the awardee:The Demountable Tokamak Fusion Core (DTFC) concept represents a unique approach to potentially commercial, normally conducting tokamak reactors. The technical features of the concept also may lend themselves to other confinement approaches employing normally or superconducting magnets. Applications of the fundamental DTFC ideas could span the range from near-term experimental devices to eventual commercial fusion reactors.

The Demountable Toroidal Fusion Core (DTFC) concept is a water-cooled, normally conducting toroidal fusion device (e.g., Tokamak) provided with joints in the toroidal field coil turns. These joints, located at the top and bottom horizontal members of each turn, permit removal and replacement of the core (e.g., central OH coil, vacuum vessel, impurity-control system, RF-heating and current-drive systems, inner blanket, if any, and PF-trimming coils). The rest of the machine (outer blanket, if any, toroidal field current return coils, and main PF coils, etc.) remains in place. This central feature has two important consequences. First, with attention to the design of the permanent outer toroidal subsystem, cores with a broad range of physics objectives can be designed, fabricated, and tested to determine the optimum physics configurations. Second, the DTFC concept is ideally suited for subsequent engineering (FERFFusion Engineering Research Facility) and commercial applications. This feature arises because the DTFC was conceived in recognition of the fact that the toroidal core is directly exposed to fusion neutron and charged particle radiation and is the subsystem most likely to fail. Provision for the replacement of the core, in a straightforward way, will significantly increase the availability of a DTFC facility for physics optimization tests and engineering and commercial applications. This could result in substantial savings in magnetic fusion R&D should the DTFC concept be pursued. The results of Phase I revealed that the DTFC Tokamak concept is feasible in all of its key areas. Using conservative scaling laws, the Tokamak ignites and is capable of long (several hundred second) pulses, driven only by the PF/OH coil system. The joints are feasible as is the tension-suppression system required to keep the Tokamak in the desired stress state during operation. Finally, neutronics analysis has shown that a sufficient breeding ratio can be achieved for a pure fusion DTFC Tokamak electric power plant. Based on the success of Phase I, Phase II will be directed at developing a conceptual design of a DTFC facility for physics and optimization and engineering tests of relatively low-aspect ratio toroidal fusion concepts.Anticipated Results/Potential Commercial Applications as described by the awardee:Phase II will result in a facility design with sufficient detail so that estimates of its flexibility, cost, and timing can be made with some confidence. Additionally, potential cost-savings in the magnetic fusion R&D program can be made should DTFC facilities for physics optimization and FERF applications be constructed after less expensive physics experiments demonstrate fusion ignition and fusion burn. The eventual commercial applications are the production of fuel for nuclear power plants, and perhaps the production of synthetic chemical fuels.