Russia developing hybrid fusion-fission reactor

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Ivy Matt
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Russia developing hybrid fusion-fission reactor

Postby Ivy Matt » Wed Oct 29, 2014 2:37 am

Temperature, density, confinement time: pick any two.

D Tibbets
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Re: Russia developing hybrid fusion-fission reactor

Postby D Tibbets » Thu Oct 30, 2014 4:38 am

This is speculation, but the only thing that currently comes to mind is the hybird reaction that occurs in hydrogen bombs, though in a more controlled leisurely way. The fission plant produces tritium from lithium in the tokamak plasma or a lithium reservoir from which the resultant tritium is harvested and fed into the tokamak along with deuterium. From there normal tokamak process apply. The difference is that the tritium is produced from neutrons from the fission reactor. The challenging first wall lithium blanket engineering with 100% efficiency in neutron capture to tritium production is greatly eased or eliminated. I think this is one of the possible road blocks to D-T fusion. you have to produce as much tritium as you consume. If the physics of the fusion process can be made to work, this tritium bottleneck might need this fission provided neutron supplement.

Dan Tibbets
To error is human... and I'm very human.

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Re: Russia developing hybrid fusion-fission reactor

Postby Skipjack » Thu Oct 30, 2014 5:05 am

I think what they are doing is to use the fusion reactor as a neutron source to keep a fission reaction going. It would allow to burn more of fission fuel, even burn nuclear waste.

RERT
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Re: Russia developing hybrid fusion-fission reactor

Postby RERT » Thu Oct 30, 2014 1:57 pm

See www.globalenergycorporation.net. This is a group of ex SPAWAR researchers aiming to produce a hybrid fusion/fission reaction by using a source of energetic neutrons to cause fission in U238. They are starting from the point of view of LENR, but the principle is the same: using a source of neutrons to sustain a fission reaction.

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Re: Russia developing hybrid fusion-fission reactor

Postby mattman » Thu Oct 30, 2014 8:51 pm

Phoenix Nuclear Labs can go 5E+11 Neutrons/Second for 24 hours continuously. Using a <million dollar machine. It could be 1E13 or 1E14 if they burn tritium.

I would not be surprised if this solution is 10X cheaper than what Russia is trying.

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Re: Russia developing hybrid fusion-fission reactor

Postby D Tibbets » Thu Oct 30, 2014 10:07 pm

To error is human... and I'm very human.

RERT
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Re: Russia developing hybrid fusion-fission reactor

Postby RERT » Fri Oct 31, 2014 6:29 pm

I searched with very little success last night to find out how much energy a fast-neutron/U238 fission might generate. The best I came up with was a reference to Plutonium 239 fission yielding over 200 MeV. That might be a practical to spin a turbine if the input energy was less than 60MeV. So if D-T fusion yields 18MeV, a fusion yield of the order of 30% of input energy would do the job to produce net power in this configuration (leaning heavily on the somewhat dubious 200 MeV figure).

D Tibbets
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Re: Russia developing hybrid fusion-fission reactor

Postby D Tibbets » Fri Oct 31, 2014 7:17 pm

It is not the question of physics so much as it is the pratical questions of safty and cost. A Jet size tokamak might make plenty of fast neutrons to push a U238 fission reaction. But-
The tokamak would need superconducting magnets or it would consume upwards of a Gigawatt of magnet power. This adds cost for the superconducting magnets. Superconducting magnets are also dangerous- if superconductivity is lost they explode with significant force, which is enough to demolish nearby structures like the fission core, or at least plumbing critical to maintaining and cooling the fission core. There is no immediate cutoff on the heat output of a fission core, The actual fission can be shut down quicky, but the radioactive decay heating ony trails off slowly, decreasing ~ 10 fold for every 7 units of time exponetially. If the radioactive decay heating at shutdown is 100 MW at shut down, at 7 hr it is ~ 10 MW, at ~48 hr it is 1 MW, at 14 days it is ~ 100 KW, etc. That is why the Japanese reactors exploded, once coolent flow was lost, this continuous core heating could not be managed.

The tokamak has to be close (wrapped around?) the fission core in order for the neutron flux to be adiquate (inverse square law). The tokamak could be a safe distance away only if the tokamak is larger- costlier, or someone figures out how to focus neutrons. This may be conservative. There is such an energy gain with fission, the neutron flux may not need to be much to generate the GWs needed to overcome losses. I think woth machines may need to be inside a common containment vessel though. The management of superconductor failures would require additional expensive measures in order to limit damage and protect the important plumbing for the fission core.

Typical fission plants produce ~ 1-2 GW of heating, with perhaps 300-500 MW of electrical output. With the incorporated tokamak, perhaps 3-4 GW of fission heat output may be needed unless the tokamak is close to Q=1 and superconductor magnets are used. The cost of the electricity would be greater than twice that of a conventional fission plant. That is before considerations of increased construction, maintenance, and decommissioning costs. Also, the radioactive storage costs may actually be greater.

If the scheme is to produce produce plutonium from U238, most of the above issues are moot. Now the chief concerns are those typical of fission power plants plus the cost of building and maintaining the tokamak. Also, the proliferation of plutonium bomb making material would be a concern. A similar set of concerns would apply to any D-T and to a lesser extent D-D fusion machine like the DPF, FRC, Polywell, Lockheed, etc. . It may be well short of breakeven but still produce plenty of neutrons with al lof the proliferation concerns.

Dan Tibbets
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RERT
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Re: Russia developing hybrid fusion-fission reactor

Postby RERT » Fri Oct 31, 2014 8:31 pm

I wouldn't want to argue with any of that: doing this with a large Tokamac sounds horrendous.

The idea in this thread is that a neutron flux can be leveraged to higher energy output using a fissionable ?U238? 'blanket'. The question is then 'How *much* leverage?'. My answer as above is that 11:1 is the best you could ever get, even if you could figure out how to solve the problems you outline. Consequently, a DT fusion plant which is less than about 30% fusion energy to input energy can't be leveraged to anything useful. The point here is to put some scale on the speculations in this thread.

In passing, I don't think the idea is to turn U238 into Pu239: you can only get that amount of energy out by having the fast neutron cause fission into much lighter nuclei.

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Re: Russia developing hybrid fusion-fission reactor

Postby Axil » Sun Nov 02, 2014 4:20 am

This idea is as old as the hills. Hans Bethe can up with it in the 1950s. But Bethe thought that a uranium blanket was a bad idea. Thorium is far better.

http://en.wikipedia.org/wiki/Nuclear_fu ... ion_hybrid

also see

http://web.mit.edu/fusion-fission/Works ... _Cycle.pdf

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Re: Russia developing hybrid fusion-fission reactor

Postby D Tibbets » Mon Nov 03, 2014 10:51 pm

Actually, the Polywell itself could end up being a fusion fission hybrid. The so called D-D 1/2 cat system is a D-D deuterium machine surrounded by a blanket of Boron 10. The neutrons are captured and the excited boron 11 then fissions into alphas and tritium giving a moderate amount of additional thermal energy. The tritium could then be collected for beta voltaic cells or other uses. If the D-D Polywell is only marginal in capacity, this fission boost may be needed to make it viable.

Dan Tibbets
To error is human... and I'm very human.

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Re: Russia developing hybrid fusion-fission reactor

Postby Skipjack » Tue Nov 04, 2014 4:34 am

Helion once intended to do a fusion- fission hybrid based on their Fusion Engine. Their cylindrically arranged pulsed reactor is very well suited for this, much better than a tokamak. They intended to "burn" nuclear waste and produce a lot of energy in the process. They found that the biggest problem with the idea was not as much technical but cultural. It was unpopular with both fission proponents and fusion proponents. Fission proponents did not want their simple fission reactors to be complicated by a fusion reactor. Fusion proponents did not want "dirty" fission near their "clean" fusion.

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Re: Russia developing hybrid fusion-fission reactor

Postby ohiovr » Wed Nov 12, 2014 3:55 am


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Re: Russia developing hybrid fusion-fission reactor

Postby JoeP » Wed Nov 12, 2014 2:43 pm



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