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Problems with Problems With The Orion Spacecraft #9: Stress
In article .com,
Jack Linthicum wrote: You must not be conversant with Ted Taylor. TRy Jamie McPhee's The Curve of Binding Energy. Taylor goes from a source the size of a softball (not specified whether the 12, 13 or 20 inch circumference) page 108, 20 pounds weight page 109, a small cantelope page 148, one gram was converted to energy in the Nagasaki bomb, page 163, home-made about the size of a golf bag page 193, the gum reference is to a stick of U-235 that size which 10% of the energy contained therein would bring down the World Trade Center, when it was still standing, page 15. All the nuke people hate Taylor as he kind of makes their brain strains into easy exercises. It's at least moderately marvellous that there was a person in the world who was to nuclear weapons design what the master-smiths of Japan were to swords; the kind of person whose intuitive understanding of implosion made him a living national treasure. It's possibly also marvellous that there was but one, he is dead, and his like unexpected to return. [though Aldermaston is very strongly hiring at the moment, if anyone here's a security-clearable Brit with an interest in very large-scale computing and not concerned about building what can only be either exercises in engineering masturbation or tools of genocide; I'm afraid I match only #1 and #2, and #3 is something of a deal-breaker] Tom |
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Problems with Problems With The Orion Spacecraft #9: Stress
In article ,
Derek Lyons wrote: With a higher velocity gun, and better ability to calculate the effects of pre-detonation, all manner of things become possible. OTOH, there have been references to 'supergrade' plutonium, I.E. having less -240 than is the norm. I don't know if the -240 is separated out or if the Pu is produced using methods that create less -240. If you have vast amounts of lightly-enriched uranium (or, I suspect, even fully-depleted uranium if you've already got a reactor producing decent neutron flux), you can cycle it through the reactor fairly quickly; you don't get _much_ 239-Pu in the result, so it's inefficient in terms of uranium usage and, more importantly, reactor and reprocessing capital cost, but you get proportionally substantially less 240-Pu. I suspect that's easier than going for actual enrichment. Tom |
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Problems with Problems With The Orion Spacecraft #9: Stress
On Mon, 24 Oct 2005 12:30:54 -0500, Pat Flannery
wrote: Paul F. Dietz wrote: Well, either the Orion team made a major slip in their report, or by 1964 we knew how to separate Pu-239 and Pu-240. ... or maybe that pre-reacting is perfectly acceptable in the low yield situation here? From what I read, what would happen is that the plutonium would go molten and start to vaporize before it could be detonated- you would probably end up with a dirty bomb more than a true nuclear bomb. I wouldn't want to be the guys who had to retrieve the pusher plate, as it would probably have been sprayed with plutonium if that happened. I was always suspicious of that stated inability to separate Pu-239 and Pu-240; our isotope separation technology is a lot more advanced nowadays than in W.W. II. Pat The "Super" grade Pu produced at Hanford during WWII was some of the most pure reactor Pu produced, largely due to the rapid fuel cycles they used at the time. It is a real balancing act, the longer you leave the U-238 slugs in the reactor, the more Pu-239 will be bred, but more Pu-240,241, and 242 will be produced as well. You can get fairly pure Pu-239 if you change the slugs out quickly, but then the costs go up dramatically, as you need to shut down the reactor, extract the slugs and put them through chemical seperation each time. This "Super" grade Pu was just barely on the edge for an extremely large scale gun weapon, in which two sub-critical masses would be fired at one another. It was huge, heavy and was still very suceptable to a fizzle. This was why the whole idea was discarded as it would not have lead to a practical weapon, and would have been horribly inefficient. Not the kind of device I could see being used on an Orion Standard seperation techniques can be used to seperate Pu240,241,242 out of Pu239, but because the mass ratio is much smaller it is much harder to do. I suspect the AVLIS could probably be used to great effect here. This part of the movie "The Manhattan Project" (The one where a kid builds an a-bomb), wasn't that far off. Kelly McDonald |
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Problems with Problems With The Orion Spacecraft #9: Stress
In sci.space.history Thomas Womack wrote:
[though Aldermaston is very strongly hiring at the moment, if anyone here's a security-clearable Brit with an interest in very large-scale computing and not concerned about building what can only be either exercises in engineering masturbation or tools of genocide; I'm afraid I match only #1 and #2, and #3 is something of a deal-breaker] Well, its not preceicely a secret why their budget nearly doubled even if the PM will not publicly say it yet. Tom -- Sander +++ Out of cheese error +++ |
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Problems with Problems With The Orion Spacecraft #9: Stress
In article , Pat Flannery says...
John Schilling wrote: Or they were paying attention to the *Very Low Yield* part. This is not something we heard here first. It has been publicly known for about sixty years now, that what happens if you try to build a Pu gun is that it predetonates, resulting in a very low yield. Normally, this is undesirable behavior and we thus don't build a plutonium gun. If a very low yield is what you actually *want*, go ahead and buuld the gun - it's a simple and reliable, if somewhat heavy, way to get a very low nuclear yield. Wouldn't you end up with very inefficient fission and a lot of unfissioned plutonium getting sprayed around? Yes, precisely. Now, just what were you imagining a very low yield nuclear explosion would be, if *not* "very inefficient fission an a lot of unfissioned plutonium getting sprayed around"? Well, OK, the early Orion proponents imagined that they'd get fusion explosions of whatever yield they needed from the Fission-Free Hydrogen Bombs That Were Going To Be Invented Any Day Now, Really!, but that seems to have not worked out real well. The techniques that actually work to produce nuclear explosions start with a critical mass[1] of highly enriched uranium and/or plutonium, and a full critical mass efficiently fissioned results in a high-yield explosion. [1] An imprecise term that incorporates lots of assumptions about things like geometry, compression, and tamping, but is measured in kilograms, not grams, for any currently plausible arrangement of these. -- *John Schilling * "Anything worth doing, * *Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" * *Chief Scientist & General Partner * -13th Rule of Acquisition * *White Elephant Research, LLC * "There is no substitute * * for success" * *661-951-9107 or 661-275-6795 * -58th Rule of Acquisition * |
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Problems with Problems With The Orion Spacecraft #9: Stress
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Problems with Problems With The Orion Spacecraft #9: Stress
: Thomas Womack
: If you have vast amounts of lightly-enriched uranium (or, I suspect, : even fully-depleted uranium if you've already got a reactor producing : decent neutron flux), you can cycle it through the reactor fairly : quickly; you don't get _much_ 239-Pu in the result, so it's : inefficient in terms of uranium usage and, more importantly, reactor : and reprocessing capital cost, but you get proportionally : substantially less 240-Pu. I suspect that's easier than going for : actual enrichment. Of course, if you cut short before you yield much pu239 (that is, before there's enough for much of it to pass along to pu240), then it's easier to separate the pu from the u, and you can just put the u back in for another run. The issue I see being that it'd be easier to separate substances with different chemistry, than to separate substances with exactly the same chemistry which differ only in mass. So presumably, several separation runs with chemistry is better than several *more* runs with centrifuge or gas diffusion or something. Or so I conjecture. Wayne Throop http://sheol.org/throopw |
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Problems with Problems With The Orion Spacecraft #9: Stress
In sci.space.history John Schilling wrote:
Well, OK, the early Orion proponents imagined that they'd get fusion explosions of whatever yield they needed from the Fission-Free Hydrogen Bombs That Were Going To Be Invented Any Day Now, Really!, but that seems to have not worked out real well. The techniques that actually work to produce nuclear explosions start with a critical mass[1] of highly enriched uranium and/or plutonium, and a full critical mass efficiently fissioned results in a high-yield explosion. [1] An imprecise term that incorporates lots of assumptions about things like geometry, compression, and tamping, but is measured in kilograms, not grams, for any currently plausible arrangement of these. Hmmm.... I though concentrated solution of Plutonium Nitrate in a good reflector would be critical near a kilogram ? No idea if it would be usable in a weapon or if you would need a special geometry. -- Sander +++ Out of cheese error +++ |
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Problems with Problems With The Orion Spacecraft #9: Stress
With the initial microgram samples of cyclotron-generated plutonium,
which was almost pure Pu-239, the plutonium gun was considered difficult but possible by Los Alamos. It would have required a gun velocity of around 3000 m/s, which would have required a long and heavy device. With the first reactor-generated plutonium, the Pu-240 problem became apparent. That was made in research reactors with lower burnups than planned for the production reactors under construction at Hanford. The Hanford plutonium was around 0.9% Pu-239. Modern 'supergrade' plutonium is around 1.5% to 3.0% Pu-239, with ordinary weapons grade plutonium at around 6.5%. Increasing gun velocity only gives you a proportional improvement in how much Pu-240 you can accept, while the gun weight is going up as something like the fourth power. A double-gun arrangement can only get you a factor of two in effective velocity. And at some point you run into a speed-of-sound limitation that requires moving to a light gas gun. That might get you a total factor of 5 over the marginal 3000 m/s device. I estimate that would allow the use of plutonium with about 0.1% Pu-240 with a 10% predetonation probability. That isn't very practical, but not completely ridiculous. An implosion device can guarantee a decent minimum yield even with predetonation. This can be large enough to ignite fusion boosting, after which predetonation isn't really a problem. If a gun device fizzles, odds are that you get no significant yield. I don't see why anyone would use isotope separation to eliminate Pu-240. If you want to use a gun, why don't you use U-235? It is much easier to separate, due to the larger mass difference. You don't need to get it anywhere near as pure, since 80% enriched uranium is better than 100% Pu-239 for predetonation. Yes, plutonium is a more efficient fissile material, but you give up any mass advantage for that when you try to use a gun. I am surprised that this would come up in connection with Orion. There you want small devices, which are already hard to make efficient. Without the compression of implosion, efficiency drops dramatically. You need a lot of devices, which means you want light weight and low cost. This certain doesn't qualify. Orion also wants highly reliable devices. A dud screws up the resonance of the shock absorption on the pusher plate, putting dangerous stress on the system. Devices vulnerable to predetonation are not appropriate. Orion also puts design constraints on the arrangement of tamper in the device, to try to directionalize the thrust. I would expect that the design constraints of a gun would interfere with that. |
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