Energy Flows in a Quasi-Isobaric Fusion-Fission Hybrid Reactor

We have examined the dominant mechanisms of energy flow in a fusion-fission hybrid reactor, which is based on a magnetically confined thermonuclear D-T plasma. D -T fusion provides a source of high-energy neutrons which are absorbed in a blanket outside the reactor. The blanket combines the functions of energy multiplication by fission of U^{238}, Pu ^{239} and U^{233 }, and tritium breeding. The fusion "driver" produces 100 MW of neutron power while the blanket provides energy multiplication of about 50. The hybrid can produce about 2000 MW of electrical power. The plasma is contained in the space between two concentric cylinders. There is uniformity in the direction parallel to the curved surfaces of the cylinders, and the confining field is purely toroidal. The plasma has a rectangular cross-section bounded by a planar electrode at one end and a thermionic emitter at the other, and cylindrical walls inside and outside. There is a modest pressure gradient, i.e., nT ~ constant. The temperature is high in the core of the plasma, where fusion occurs, but falls to low values near the walls and end-plates. It is hoped that the quasi-isobaric character will eliminate serious instabilities, and that plasma behaviour will be near-classical. The high-n, low-T periphery should reduce damage to the walls from energetic plasma particles. We have found a class of sustainable MHD equilibria with Q ~ 0.3. The inner and outer radii and height of the reactor are 31, 38 and 7 metres respectively. A high magnetic field is required, in the range 200-400 kG. T rises from 200 eV at the walls to 2.7 keV in the fusion zone, where n_ {rm e}~ 1.5 times 10^{14} cm^{-3}. There is a small vertical flow velocity to provide fueling. We have studied alpha-particle slowing down, electron-cyclotron radiation transport, inelastic reactions, bremsstrahlung, conduction, convection, and heat exchange between electrons and ions in the reactor. RF heating in the lower hybrid range can balance the differential energy equations for electrons and ions throughout the reactor.