The Fountain Fusion/Fission Hybrid Reactor.

[Axil]

Background:

When you have a jet of water aimed upward in a pond and the nozzle is slightly under the surface, you get a big hump of water shaped like the top of an egg. These can be quite large and sometimes you see them in sewage treatment or decorative fountains. The height is determined by the nozzle exit velocity (and gravity) and the diameter is determined by the flow rate.


So use a large parabolic shaped bowl set in a flat table (like a bathroom sink) with a big a pipe run up through the bottom at its center, with the volume of the bowl too small to achieve criticality. The overflow of the bowl runs over the side and down, passing through integral heat exchangers and then back to the infeed of the large centrifugal pump.


When the pump is running you should get a big fountain effect, turning the volume in the bowl into a big mounded egg shape and raising the core to criticality. The volume in the core is determined by the pump velocity (easily controlled) and would ebb within a second of turning off the pump. Any leakage or blockage would reduce the flow volume and thus the size of the core.


You could run single fluid of dissolved nuclear waste in a molten salt stream.


One important advantage of this reactor topology is that the nuclear fission reaction shuts off almost immediately upon power failure, with the size of the roughly spherical nuclear core determined dynamically by a fast acting control system. Another advantage is that a major perturbation in temperature or sudden a outgassing event in the core would tend to reconfigure the core into a non-critical shape, as the core is a dynamic mound above the natural height of the fluid bowl.


You could also include a low melting point alloy in the pump vanes (an extra fail safe) or in the exit nozzle, or even change the exit pattern of the nozzle with bimetallic deflection elements to help shape the core based on fluid temperature.


this system required pumping very radioactive and highly viscous core fluids, and the exact core shape will slightly vary from moment to moment. The High viscosity of the core fluid would provide a good level of topological inertia to retain a shape that would support stable reactor criticality.

The upcoming series of posts will describe how this fountain reactor concept will support a wide array of possible fission/fission hybrid topologies base on various low fluence neutron producing small fusion architectures including polywell, but first a number of supporting concepts but first be introduced.

[Axil]

For the scientists working on fusion power, such as those involved in the multi-billion-dollar Iter experiment in the south of France, neutrons are a nuisance. But researchers at Culham, the UK centre for fusion technology in Oxfordshire, are designing reactors specifically to make neutrons and have set up a spin-out company called Tokamak Solutions.

The company’s name comes from the ring-shaped tokamak reactor, invented in the Soviet Union in the 1950s, which holds fusion fuel in place as an ultra-hot plasma using powerful magnets. In the 1990s Culham researchers redesigned the reactors into a compact spherical form, much smaller than the huge reactors developed for energy experiments. Tokamak Solutions is now optimizing these for neutron production.

Its first reactor, with an outer diameter of 1.5m, could be ready to produce 2MW of neutrons within three years, says David Kingham, the company’s chief executive. The output could be used for scientific research or to prepare medical radio-isotopes, as an alternative to other neutron sources such as particle accelerators.

The second phase will be to generate neutrons that could bombard nuclear waste and transmute the most dangerous isotopes into something easier to handle. Mikhail Gryaznavich, chief scientist at Tokamak Solutions, says isotopes called minor actinides are the most tempting target.

“Burying minor actinides is expensive and risky, as they undergo fissile decay over thousands of years, releasing heat and radioactive fragments, making them difficult to contain,” he says. “Our compact neutron source is the first system based on currently available technology with the potential to produce the neutrons required for this clean-up.”

The most distant – and potentially the most valuable – application will be to use the neutrons as an intense heat source to help generate hydrogen from water as a carbon-free fuel

The low density gas fill in the fountain Cascade Subcritical Molten Salt Reactor (CSMSR) affords a serendipitous opportunity to use neutrons from fusion to drive the subcritical fission reactions as amplified by nuclear waste.

This neutron source could replace the ADS to drive the CSMSR. When coupled with a uranium carbide parabolic neutron reflector, these high energy neutrons could be directed into the center of the fountain chloride molten salt high temperature core.

The “rays of 14.2 MeV D-T fusion neutrons” would converge and focus at the center of the fountain based CSMSR reactor core in the same way that a gamma ray telescope focuses high energy radiation onto a focal point. Using the countless layered cubic crystal surface structures of uranium carbide, alternating layers of carbon and uranium will provide a large array of reflecting surfaces that would redirect the high energy neutron wave forms to penetrate into and converge at the center of the fountain CSMSR core.

[D Tibbets]

I think I can see your reasoning with the fountain, where the two (three) interacting actions is potential (velocity) , flow (volume), and gravity (sort of containment or limiter). But what is not included is heat. As the criticality is approached the heat generation will increase rapidly and this would tend to disperse the fission fuel. Whether you could reach some useful edge density is the question. You would also need to pay attention to the drainage flow/ volume. For that matter, would the density in the fountain shell be greater than the density as the fuel exits the nozzle?
Also, inertia may be important. If criticality is passed, how much fuel burnup (fission) would occur before the fuel dispersed. Would it be vaporized? With resultant highly radioactive gasses? Would vapor deposition be a problem?


Dan Tibbets