I was thinking. Since for a power reactor we will need to water cool the coils. Suppose we made the water jacket thick enough to thermalize neutrons. And then had a B10 layer to absorb them.
It should be possible to cut way down on coil damage and still run superconductors in a D-D machine.
MgB is interesting in that it becomes a better superconductor with some neutron damage - I think critical temperature goes down though. I would have to look it up.
D-D and Superconductors
D-D and Superconductors
Engineering is the art of making what you want from what you can get at a profit.
With MgB the resistivity goes up. Critical Field goes up. And critical temperature declines slightly.
The main problem seems to be defects caused by B10 absorbing neutrons.
If B10 was used in shielding and B11 used to make the superconducting wire much longer lifetimes in neutron fluxes should be possible.
The difference is six orders of magnitude B10 to B11. With B10 @ 10,000 barns at .025 eV and B11 @ .01 barns.
http://en.wikipedia.org/wiki/Image:Neut ... nboron.png
Magnesium has a cross section of about .75 for 2.5 MeV neutrons
Mg is .063 Barns for Thermal Neutrons.
http://environmentalchemistry.com/yogi/ ... ction.html
Which says that if we can get an operational life of the superconductors at 10 hours with ordinary Boron, a year should be possible with five to six nines pure B11.
Reduce the Flux another factor of 10 with water moderation and a B10 absorption layer and you are up to 10 years operation. Double that Boron 10 thickness and you are up to 100 years. Which should allow for various inaccuracies and production variations.
The main problem seems to be defects caused by B10 absorbing neutrons.
If B10 was used in shielding and B11 used to make the superconducting wire much longer lifetimes in neutron fluxes should be possible.
The difference is six orders of magnitude B10 to B11. With B10 @ 10,000 barns at .025 eV and B11 @ .01 barns.
http://en.wikipedia.org/wiki/Image:Neut ... nboron.png
Magnesium has a cross section of about .75 for 2.5 MeV neutrons
Mg is .063 Barns for Thermal Neutrons.
http://environmentalchemistry.com/yogi/ ... ction.html
Which says that if we can get an operational life of the superconductors at 10 hours with ordinary Boron, a year should be possible with five to six nines pure B11.
Reduce the Flux another factor of 10 with water moderation and a B10 absorption layer and you are up to 10 years operation. Double that Boron 10 thickness and you are up to 100 years. Which should allow for various inaccuracies and production variations.
Engineering is the art of making what you want from what you can get at a profit.
Although we would want 11B, not 10B, it looks like standard nuclear reactors already do a Boron solution (e.g. Boric acid in PWRs): http://en.wikipedia.org/wiki/Boron#B-10_enriched_boron
10 B has a Maxwellian thermal neutron flux cross section of almost 4,000 barns.dch24 wrote:Although we would want 11B, not 10B, it looks like standard nuclear reactors already do a Boron solution (e.g. Boric acid in PWRs): http://en.wikipedia.org/wiki/Boron#B-10_enriched_boron
11 B is around .1 barn.
At room temperature Borax B(OH)3 is soluble at about 57 g/ liter. Which is about 9.3 g/ liter of B10.
Maximum properties of MgB occur at 2E18/cm^2 total neutron flux. Let us say 1E18 and have some safety margin.
Typical fission reactor neutron flux is 1E12/second. Let us say because of the lower energy per reaction a D-D reactor would have 50X that flux.
So that is 20,000 seconds at full power with natural boron. Say 4 1/2 hours. If we go to B11 superconductors assume a 1,000 time improvement. That is 4,500 hours. Say 6 months roughly. So we need a B10 shield that can reduce the neutron flux at the coils by a factor of 10. Giving a life of 5 to 7 years continuous operation.
Since MgB is cheap, replacing the coils every 5 to 10 years should not be a big burden. In addition preconditioned coils capable of sustaining 30 T might get a premium.
Update: Revised solubility. Revised superconductor neutron flux stuff.
Last edited by MSimon on Sun Jan 27, 2008 8:30 pm, edited 1 time in total.
Engineering is the art of making what you want from what you can get at a profit.
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Munchausen
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Perhaps lead cooling of the outermost layer of the coils is an option? Then it could be kept at zero pressure. Or at least no more pressure than is needed to keep the coolant flowing. Which may be an advantage. It should also give some neutron shielding.
http://en.wikipedia.org/wiki/Lead_cooled_fast_reactor
This technology was originally developed at the Admirality ship yards in Leningrad together with a titanium hulled submarine and an underwater rocket capable of several hundred knots. The submarine could dive down to 900 meters and reach speeds of +40 knots.
It gave the russians an advantage for a short while. But it ultimately failed. A kind of engineering pyrrhic victory. It must have taken an unbelieveable amount of engineer work hours to accomplish.
The lead-bismuth coolant is highly corrosive. This might be overcome with something called "active oxygen"-technology but it is not known how it is really done.
The Royal School of Technology in Stockholm has built an electrically heated test rig to sort the material problems out. Finansed with money from the EU. I have seen it myself. The guy in charge of the project said that the corrosion problems were not easy to overcome. As you can imagine the russians are willing to give little or no advise on the matter.
http://en.wikipedia.org/wiki/Lead_cooled_fast_reactor
This technology was originally developed at the Admirality ship yards in Leningrad together with a titanium hulled submarine and an underwater rocket capable of several hundred knots. The submarine could dive down to 900 meters and reach speeds of +40 knots.
It gave the russians an advantage for a short while. But it ultimately failed. A kind of engineering pyrrhic victory. It must have taken an unbelieveable amount of engineer work hours to accomplish.
The lead-bismuth coolant is highly corrosive. This might be overcome with something called "active oxygen"-technology but it is not known how it is really done.
The Royal School of Technology in Stockholm has built an electrically heated test rig to sort the material problems out. Finansed with money from the EU. I have seen it myself. The guy in charge of the project said that the corrosion problems were not easy to overcome. As you can imagine the russians are willing to give little or no advise on the matter.