Sciencemadness Discussion Board - Nuclear Reactions

Nuclear Reactions

Organikum - 11-4-2006 at 21:12

I am more and more concerned about how nuclear power is provided to the public.

I am on a loss why it is told that centrifuges and shit are necessary to build a working reactor or bomb.

It is known that uranium enriched to about 30% with sufficient shielding is to make a bomb.

30% is about natural in certain ores.

Am I on a loss here?

Polverone - 11-4-2006 at 21:52

Rich uranium ores could contain ~30% elemental uranium, but I don't think there are any natural materials that contain U-235 enriched to ~30%. Without enrichment, you can make a self-sustaining reaction for power production or transmutation, but it needs to use a very good neutron moderator like high-purity graphite or heavy water. If the uranium is isotopically enriched by centrifuge or otherwise then it can be used in a light water reactor. I don't think it is at all possible to make a nuclear bomb from uranium without heavy isotopic enrichment. It's possible to split natural uranium with fast neutrons for a great release of energy, but the only neutron source intense enough to make a usable weapon that way is a thermonuclear explosion, which itself needs a fission trigger. So it is possible to build a reactor without uranium enrichment, but it is less common. It is not possible to make a uranium fission weapon without isotopic enrichment.

[Edited on 4-12-2006 by Polverone]

a_bab - 12-4-2006 at 02:08

The U235 which is the lighter explosive izotope it's always found in a 0.7% percentage, no matter what ore from what region of the world.

leu - 12-4-2006 at 03:27

Disposal of nuclear wastes remains a rather troubling problem, centrifuge separation remains the only feasilbe process for commercial production of enriched fissile material. Some links with some facts and opinions that may be helpful:

http://www.world-nuclear.org/info/printable_information_pape...

http://www.uic.com.au/nip33.htm

http://www.llnl.gov/str/Hargrove.html

http://www.llnl.gov/str/Strauch.html

http://www.fas.org/nuke/intro/nuke/uranium.htm

http://www.fas.org/RLG/v095pcwp.htm

http://www.earthisland.org/yggdrasil/uep11_01.html

http://www.nti.org/db/nisprofs/russia/exports/rusiran/nukede...

http://www.nti.org/db/china/uenrich.htm

http://www.francenuc.org/en_chn/enrichment_e.htm

http://www.absoluteastronomy.com/ref/nuclear_fuel_cycle

http://www.absoluteastronomy.com/ref/isotope_separation

http://nuclearweaponarchive.org/Israel/

http://nuclearweaponarchive.org/Nwfaq/Nfaq6.html

http://www.photonics.com/content/spectra/1997/October/tech/7...

http://www.ornl.gov/info/ornlreview/v37_1_04/article_04.shtm...

http://cns.miis.edu/pubs/week/041109.htm

http://www.wise-uranium.org/eproj.html

[Edited on 12-4-2006 by leu]

[Edited on 12-4-2006 by leu]

MargaretThatcher - 12-4-2006 at 04:42

Natural uranium like the other elements from which we are composed is the leftovers of a supernova. Hence metorites etc. have the same ratio as found on earth. The only natural places on earth where the isotope ratio is different are the natural reactors such as in Gabon.

The enrichment necessary to sustain a chain reaction depends on the moderator used: with a graphite or heavy water moderator, natural unenriched uranium can be used (as used by Fermi in the first man-made reactor and Chernobyl). With a water moderator, the isotope ratio needs to be several percent as it was a 1.5 billion years ago, allowing natural reactors to occur in uranium deposits.

Uranium enriched to 3.5% for use in water moderated reactors is not weapons grade. Weapons grade is at least 85% 235U, but 20% is sufficient though very inefficient for a bomb.

12AX7 - 12-4-2006 at 06:24

I want a few tons of natural uranium (in whatever form, oxide pellets would be fine), and about as much graphite. And some boron or cadmium. It would be fun to make backyard plutonium.

Tim

vulture - 12-4-2006 at 07:24

Ofcourse the nuclear weapons threat is bull. Unless you believe that the US will supply India with special centrifuges that can in no way be used for malevolent enrichment. But you would still have to answer the question why they wouldn't be selling those to Iran.

Anyway, the whole debate is pointless as Iran will be attacked by the neocons anyhow, nothing is going to stop that. Iraqi and Irani citizens, will, as usual, pay the price.

Meanwhile oil prices skyrocket which means more money for the Bush clique. Smart, isn't it?

MargaretThatcher - 12-4-2006 at 15:01

Yeah vulture, Iran is years away from enriching enough uranium to make a practical bomb. Even if it had a bomb, it would be more of a defence against US and Israeli aggression than an offensive thing. One way to stop them building such a weapon would be to be nice to them and stop threatening them.

12AX7 - 12-4-2006 at 15:25

Yeah, but they've been hate-mongering for *decades*. I mean, just about everyone is Muslim, and just about everyone goes to a mosque where several times daily the people are told to hate Americans. At least, that's what they said on the History Channel, a rather partial channel as television goes. Whether or not you believe it, hearing it that much is going to warp your mind.

Tim

Rosco Bodine - 12-4-2006 at 18:26

Quote:

Originally posted by MargaretThatcher
Yeah vulture, Iran is years away from enriching enough uranium to make a practical bomb. Even if it had a bomb, it would be more of a defence against US and Israeli aggression than an offensive thing. One way to stop them building such a weapon would be to be nice to them and stop threatening them.

It is for certain that Iran already has a nuclear weapon and its inert remains are guaranteed to be found as evidence amidst the rubble from the preemptive strike which will be necessitated to prevent its use ....just in the nick of time , you see . So it was never a matter of preventing them from developing it , but from using it .....that thing they should have never even thought about . After all we are the thought police , so people should be careful what they are thinking or we might get ideas of our own . Regime change is what is needed in Iran . Hey here's an idea , lets not invade Iran on the pretext of any noble cause ....but simply for the joy of raping and pillaging . Sounds like a plan

[Edited on 13-4-2006 by Rosco Bodine]

Polverone - 12-4-2006 at 18:52

This started out as a technical question but seems to be teetering on the edge of Shit Canyon like a few other threads we've just had. Please keep the political fisticuffs to the designated forum.

Marvin - 13-4-2006 at 15:45

Iran maybe years away from enriching enough uranium to make a bomb, but if you are going to develop nuclear weapons in defience of the US you do it the way the UK did it when it developed nuclear weapons in defience of the US.

Build a reactor, poison the villagers and make a plutonium bomb. Didnt half make the US upset, they imposed trade restrictions when they found out, tried to throttle the UK economically the way the rest of the world was throttling Iraq. Of course, its not popular to remind people of this anymore. The US is embarrased it ever tried to the stop the UK getting nukes - but only now they have them, and the UK is embarrassed the air cooled reactor it resorted to on the basis of time contraints caught fire or leaked lethal clouds of dust from the core so many times.

The main thing is that everyone that gets nukes wants to be the last. Noone thinks anyone other than themselves can be trusted with them. The sad fact is, every country that wants them will get them eventually. The best long term solution would be to lead these countries to the path of stability as they aquire them, not invade everyone that blinks twice when whichever inbred hick of a US president says nu-cu-lur.

MargaretThatcher - 13-4-2006 at 17:55

"Build a reactor, poison the villagers and make a plutonium bomb. Didnt half make the US upset, they imposed trade restrictions when they found out, tried to throttle the UK economically the way the rest of the world was throttling Iraq. Of course, its not popular to remind people of this anymore. The US is embarrased it ever tried to the stop the UK getting nukes - but only now they have them, and the UK is embarrassed the air cooled reactor it resorted to on the basis of time contraints caught fire or leaked lethal clouds of dust from the core so many times."

That is rather erroneous.

Pommie - 14-4-2006 at 07:15

Can someone explain what is so hi tech about these centrifuges? Surely, anything that could be built in the 40's can now be built by the average Joe in his garage? Is it just a problem of scale thing? Also, if you get hold of a ton of Uranium and process it to get 9Kg of 235, can you then sit the 238 around the 235 and make yourself some Plutonium?

Mike.

vulture - 14-4-2006 at 09:25

Quote:

You're crazy if you think Iran would use a nuclear weapon as a means of aggression. They'd maybe take out Tel Aviv and then what? They get wiped off the face of the earth by the Israeli Nukes (which no one seems to object to) before they even could survey the damage.
They're crazy, but they're not stupid. They hatemonger against the US because it keeps the population from seeing their ineptness to lead a country, not because they want to attack the US.

That said, what do you think will happen after a strike on their installations? Insurgency in Iraq will skyrocket along with US casualties. More moderate islamic countries will also turn against the US.

Want to attack Iran? Fine, just don't come whining for help after you've stirred up the hornet's nest. We warned you guys about Vietraq...
Solving problems that aren't there only creates problems.

IIRC uranium enrichment centrifuges concentrate UF6, which makes it somewhat more complicated than solid centrifugation. That said, it was possible in the 40's, so...

[Edited on 14-4-2006 by vulture]

I am a fish - 14-4-2006 at 10:57

Quote:

Originally posted by Pommie
Can someone explain what is so hi tech about these centrifuges?

They aren't just any centrifuge. To isotopically seperate uranium, accelerations of the order 1,000,000g are required. This is a major engineering feat.

The rotor in such a centrifuge will spin in excess of a thousand revolutions per second. To overcome friction, it will need to operate in vacuum, and will require extremely advanced bearings along its drive shaft. It will also need to be extremely well balanced, as even a minute inbalance in mass will cause a colossal imbalance in force

The materials used in the rotor are pushed to their mechanical limits and so must be of superlative quality. Forging a metal that won't disintegrate under the strain is an engineering feat in itself (and indeed, metals of the required quality are sometimes referred to as "centrifuge grade"). If any part of the rotor does fail, it will explosively disintegrate, with chunks of metal being thrown out at supersonic speeds.

Finally, such a device must operate whilst an extremely toxic and corrosive gas (uranium hexafluoride) is being simultaneously pumped into and out of it.

a_bab - 14-4-2006 at 11:09

"Surely, anything that could be built in the 40's can now be built by the average Joe in his garage? "

I'm sorry, but that's pure crap.

Would you be able to make liquid air in your garage? It was done more than 100 years ago.

Or how about an 30 KW arc furnance Moissan used to make? Can you isolate lithium from mineral waters?

There are countless examples of old things the average Joe wouldn't be able to make, let alone in the garage. It's a matter of resources rather than knowledge.

[Edited on 14-4-2006 by a_bab]

Marvin - 14-4-2006 at 11:39

Actually a_bab liquid air woud be quite trivial in a garage, as would be an arc furnace.

Materials that will withstand 10,000rpm centrifuge operation and not be corroded by UF6 gas though are still rather exotic. Just making UF6 would require the ability to handle fluorine.

I do wonder if single crystal steel technology would work, but thats usually limited to tiny parts inside jet engines.

MargaretThatcher, If there are specific faults with it, feel free to correct them. US refused to release details of the bomb to the countries that helped develop it. The first windscale pile went critical in 1950, with an air cooling system later found to leak radioactive particles. When US found out the UK were building a bomb, talks broke down and they threatened trade sanctions unless they stop. They may not have had time to apply them, the plutonium produced was augmented with purchased plutonium from canada and 'hurricane' was detonated just two years after the first windscale pile went critical. Just a few years later, still producing plutonium for the bomb project one of the two reactors caught fire, resulting in the release of massive amounts of radioactive iodine and polonium (the latter being manufacturered for the bomb triggers).

All this is a matter of historical record.

If you want nuclear weapons, don't enrich! Build a pile! Its not safe, but it is fast. UK was a nuclear power before it had nuclear power and against the wishes of the US.

akinmad - 14-4-2006 at 12:30

Quote:

Originally posted by Marvin
I do wonder if single crystal steel technology would work, but thats usually limited to tiny parts inside jet engines.

I recently translated Nuclear Material Trigger List of IAEI. This is a list by which IAEI watches if a specific country is a proliferator.

In certain parts of a very long list, there was an article mentioning about nickel alloys, which are placed in the trigger list for they are resistant to UF6 and heavily used in both diffusion and enrichment centrifuges.

For obtaining hints about nuclear technology, I recommend taking a look at that trigger list. HTH. Regards.

unionised - 14-4-2006 at 12:33

"Actually a_bab liquid air woud be quite trivial in a garage, as would be an arc furnace."
Have you tried?
Once you have got that sorted out you might want to try making a copy of John Harrison's chronometer.
Anyway.
Surely the problem isn't nuclear weapons?
Imagine the West gave Iran a nuke as a present.
Then they reminded the Iranians that, if they ever used it, they would get wiped off the face of the earth in retaliation.
Most plausible governments would probably not want to try firing it.
Even if they did their neighbours would put a lot of effort into stopping them.

Iran can't even maintain decent roads- their rail system is shot and their healthcare isn't much better.
It simply doesn't make sense to let them build a nuclear power plant; Windscale, TMI and Chernobyl (and the French and Japanese ones that I can't remember the names of) taught us it's difficult to build a safe one, even if you have reasonable infrastructure and good engineering. We should be telling the Iranian people that, since they have lots of oil, they don't need nasty dangerous, expensive nuclear power. (And the first one to disagree about the cost gets beaten to death with the slogan "too cheap to meter"). While we are at it me might ask them if they need a government that is prepared to risk the citizens' lives for an ego trip. (er, actually, come to think of it, that probably goes for the US and the UK too)

12AX7 - 14-4-2006 at 14:49

The physics prof at my school keeps talking about building bombs. He said one class accomplished the task of designing a bomb, inside and out, presumably, calculating cross sections and critical mass and kinetic energy (i.e. explosives) needed to detonate this thing and whatnot. A mini Manhattan project I guess, but without the groundbreaking physics research (it's already been done!) and unfortunately, no active materials. *Shrug*, it's just textbook information, all you have to do is assemble it. An academic curiosity.

The best way to go about nuclear anything IMO is natural uranium, requiring a minimum of refinement, combined with a graphite and/or water moderator (natural water could be used for cooling a graphite moderated reactor, but heavy water is preferrable because normal water tends to absorb neutrons) and I guess boron or cadmium control rods. Let it cook for a while and monitor the activity. After a while, it should start heating up as U238 is kicked up to Pu239, which can then be chemically refined far easier than U235 from U238.

For that matter, since H2O absorbs neutrons, you should be able to cook the whole pile with H2O and graphite and chunks of uranium fuel and, after a probably much longer time, get D2O, Pu239 and so on.

Not to mention all those wild byproducts, ranging from oh I don't know, taking arbitrary bounds of yields, say, atomic mass numbers 85-110, and uh, a minima around 123, and then about 127-152, corresponding to (assuming only beta decays to stable products) Kr to Ag and Te to Sm, plus little bits of lots of stuff all around. (I think pH would generally rise from all the alkali and alkaline earth metals produced.) Probably a good bit of trouble with residual activity of a lot of those, though. It would be neat to look through those nucleides and see which have a short half life (under a year, say) before decaying to a mostly stable nucleide (more than 10^9 years or so), then chemically seperate them after leaving the spent fuel to cool down for a while.

Reactor design wouldn't be that hard, you just need to keep everything sealed and shielded. American reactors all have very thick concrete reactor containment buildings, not a bad idea. A sealed stainless steel vessel with an extra container beside it to divert pressure in event of shit hitting the fan, and on top of that, another vessel sealing both in, would be pretty nice I think. Add feedthroughs for pipes, wires, etc., then wrap it with an inch or two of lead sheet or a couple feet of concrete. Radiation hardened robotics and cameras would be a pretty good idea for manipulating things you can't handle in the design with servos and whatnot.

Tim

[Edited on 4-14-2006 by 12AX7]

Chris The Great - 14-4-2006 at 21:11

For the centrifuge thing:

It was done in the 40's, requiring billions of 40's money (it would be massive amounts of $$$ today) and an entire CITY and a massive industrial commitment. Not something you can do in your garage. Centrifuging UF6 requires numerous stages and cannot be done on any sort of scale on anything short of a massive sized industrial plant.

For fun, calculate the ENERGY required to run those centrifuges and seperate out all the UF6. You'd need your own 500kV three phase feed line to run it!

Just because it was done in the 40's doesn't mean it is possible nowadays. I mean, if countries will massive amounts of money, engineers and such (even a poor country can get quite a few) can't do it, you're sure as hell not going to do it in your garage unless you are a freaking mastermind with millions of dollars and massive amounts of time, equipment and minions.

Designing the basics of a nuclear bomb, IMO, is not hard. In fact, I think all parts of a bomb, EXCEPT the crucial core of uranium or plutonium, could be assembled by someone such as us, assuming a implosion type single stage fission weapon of roughly 10-30kT. It would be a very large challenge but I think it could be done.

I have done a lot of research into the possibility of doing it at home, and have come to the conclusion it simply can't be done in your garage, unless your garage is massive and you have millions of dollars to spend.

It is dissapointing, but hey, you CAN do bio weapons in your garage, so if WMDs are your thing...

a_bab - 14-4-2006 at 23:31

The implosion system for a Pu or U core is also going to be a problem. Even if you can get the 30 kg or so of RDX and a slower explosive, detonating them in the proper time frames - now that's going to be a problem. You'll have to make very precise blasting caps, and a "AP filled christmas light initiated drink straw" is not going to work here.

Chris The Great - 14-4-2006 at 23:41

Yep, HV capacitor initiated exploding bridgewire slapper type detonators, or something to that general effect, are needed. I never said it would be easy, but making 100 of those, and having them fire within milliseconds of each other, is still a simple task compared to making the Pu or U core for the device.

a_bab - 15-4-2006 at 03:20

It's not as simple since the americans worked alot on this issue while the Pu was cooking... I don't know exactly what the limit of the explosion between the caps is, but I feel is under 1 ms.

EDIT: quote from Wiki

"The lenses must be accurately shaped, chemically pure and homogeneous for precise control of the speed of the detonation front. The casting and testing of these lenses was a massive technical challenge in the development of the implosion method in the 1940s, as was measuring the speed of the shock wave and the performance of prototype shells. It also required electric exploding-bridgewire detonators to be developed which would explode at exactly the same moment so that the explosion starts at the centre of each of the lenses simultaneously (within less than 100 nanoseconds). Once the shock wave has been shaped, there may also be an inner homogeneous spherical shell of explosive to give it greater force, known as a supercharge."

[Edited on 15-4-2006 by a_bab]

unionised - 15-4-2006 at 05:05

"The implosion system for a Pu or U core is also going to be a problem. "
Unless you do it the easy way, don't use one, and build a gun type device. OK it needs more Pu or U but since it's just an academic exercise that doesn't matter. After all if you can get the first kilogram the second one is easy.

akinmad - 15-4-2006 at 06:25

Quote:

Originally posted by unionised
"The implosion system for a Pu or U core is also going to be a problem. "
Unless you do it the easy way, don't use one, and build a gun type device. OK it needs more Pu or U but since it's just an academic exercise that doesn't matter. After all if you can get the first kilogram the second one is easy.

As far as I know gun type device cannot be made with Pu, since Pu needs faster assembly timing than U, due to neutron cross section (???).

IIRC, during Manhattan project, they determined a gun type device shall work and did not even test it. But calculations indicated that Pu cannot be used in a gun type device and they developed, implosion system.

[Edited on 15-4-2006 by akinmad]

12AX7 - 15-4-2006 at 09:17

I remember something like that. I don't happen to remember which metal goes with which.

+/-100ns is easy to get electrically, so it's up to you explosives chemists to figure out the lens itself.

Tim

a_bab - 15-4-2006 at 11:03

It's a matter of getting the detonator detonate at an exact moment, +/-100ns.

The problem is that usually it may take some time for a lasy detonator to perform it's function when needed (that is, the delay of let's say 200 ns is going to ruin the bomb, and even if the lens will go off the Pu would fail to go overcritical and will become part of a 'dirty bomb')

IrC - 15-4-2006 at 12:12

Less than 20 percent U235 will go critical. http://www.sciencemadness.org/lanl1_a/lib-www/la-pubs/003394...

Gas diffusion was used in the 40's, where the lighter 235 was more likely as a gas fluoride to travel through the pores in a sintered bronze wall than the 238 was. There was nowhere near the high tech needed then to build the modern centrifuges. The Pu device needs rapid assembly as the Pu241 impurities even in trace amounts make so many neutrons it fizzles the bomb before assembly. One way around this may be explosive driven collapsing rings.

There seems to be much speculation going on about all this and it is easy to find some useful information.

One place you may gain some insight is: http://nuclearweaponarchive.org/Nwfaq/Nfaq0.html

hinz - 15-4-2006 at 12:38

Quote:

Originally posted by a_bab
It's a matter of getting the detonator detonate at an exact moment, +/-100ns.

Why not just using some detonating cord. If you would take one chuck of some kind of explosive and stick as much det. cords in it as you need detonators. The delay you would be able to controll with the lenght of the cord, longer cord=>more time till the detonation reaches the explosive around the bomb. The little differences in the VoD doesn't matter, I think. The only problem is that you need some distance betwen the cords to prevent that the detonation moves from one cord to another.

Chris The Great - 15-4-2006 at 13:18

That is actually a very good idea. But I don't know if det cord has the proper tolerances... I guess you could buy a bunch and measure it's VoD 100 times and see how much error you get...
Still, exploding bridgewires on a 10kV pulse cap with a few thousand joules of energy is going to get the tolerances right if fired with a sparkgap switch. The problem would be making sure the exploding bridgewire hits every cap equally, not whether they all explode simultaniously.

While it is true that 16% U-235 will go critical, remember the critical mass they found was "only" 692kg of it. The size of the explosive charge to drive that and the engineering difficulties in making it... plus getting that much uranium... And then the final size of the bomb

Gas diffusion requires even larger plants than centrifuges. 40's tech, not ultra-complex, but still wholly impractical.

The collapsing ring thing is old news I thought, at least I got the impression it has been around for a long time.

IrC - 15-4-2006 at 15:06

I am sure it is even older than we know, but I notice it does not get mentioned much in Pu assembly time conversations for some reason or other.

Marvin - 18-4-2006 at 16:53

Det cord in various forms was tried during the manhatten project. It simply isn't good enough.

I suspect something like a marx circuit would work as an electrical system.

I dont know anyone who would have the first clue how to design an implosive lens though.

Chris The Great - 18-4-2006 at 18:49

Thanks for the info on detcord Marvin. Got a source or anything on it? It could (unlikely) be that their det cord simply was 50's stuff and sucked. The fact they said it can't work means nobody else looked into it... a lot of old stuff is like that for us "amatuers".

The concept of an explosive lense is quite simple and can be solved by simple trigonometry. The explosive lense is basically a cone, the inner explosive is a low VoD type and then there is a layer of high VoD explosive on the outside. The high VOD explosive detonates much faster and as it detonates it initiats the low VoD explosive- the outside detonates faster than the inside. This, when done correctly (you need to work out the rations for whatever explosive is used) forms the detonation into a piece of a semi-circle. With many cones on the surface of a sphere, you get a spherical implosion wave.
I have designed one, it was actually fairly small, but the design was very straightforward.

The concept is covered in Brassey's World Military Technology; Explosives, Propellants & Pyrotechnics, starting on page 36. It covers several methods of wave shaping as well as a type of implosion device. You'll notice that the design can be streamlined to the one I describe above by simply removing the excess high VoD explosive not needed to transmit the detonation.

The challenge comes in making your entire explosive lense assembly uniform. You can't have any varying densities in the explosives, etc. It is more of an engineering problem than a design one. You'll need to check all your VoDs beforehand as well.

Idea: for testing your implosions system, use Xrays. A steel tamper will allow you to "see" the center of the bomb, which you could put something like tungsten or other VERY dense material in. The steel will be visible from the sides, but not from the middle, so you can see if it collapses evenly! Difficult, yes, but you're building a mock nuke implosion system.

Mr. Wizard - 19-4-2006 at 11:32

This web site is one of the most comprehensive you will ever find. It is full of details that will educate and amaze you. If anyone knows of a better one, please let us know.
http://nuclearweaponarchive.org/

I love this quote:

"...And these atomic bombs which science burst upon the world that night were strange even to the men who used them."

H. G. Wells, The World Set Free, 1914

Chris The Great - 19-4-2006 at 15:23

I remember the site now! It is a great collection of information. I printed off the entire thing several years ago. It had since slipped from my memory.

It is a great site for understanding the basic to more advanced concepts of nuclear weapons. I have never seen a site that even comes close to it.

Marvin - 20-4-2006 at 01:58

I don't have a reference for the detcord, it was a casual remark from someone else who looked into the technology more seriously and shattered the (I thought) rather cunning design I had in my head.

The basic science behind the implosive lens is quite simple and given the refractive index of a transparent material n is the ratio of c to the speed of light through it, I'm sure convensional lens making math would give *an* answer.

The first major problem I have is that the tabulated speed of a shockwave through the material depends not only on the density but also the degree of confinement, steel versus copper tubes, how wide the tube of explosive is and the answers seem barely accurate to 10% under even the best circumstances. I have no idea how to model a shockwave through bulk material. I did wonder about working out the values to a focal point and then testing on steel plate to refine the numbers.

The second major problem I have is not only is it about focusing the expanding shockwave segments so they converge on the core, its also about turning the convex wavefront produced by the detonator into a concave one so you have a spherical implosion, a solution I don't think is automatically satisfied by solving problem one (whats to stop the inner and outer edges of each det wave segment reaching the same point at the center, but at different times?). This to me seems akin to controlling the phase of an optical wavefront as well as its direction and is the sort of problem that wants to make my brain try to escape through my ears. All using a medium with a det velocity that depends on the strength of the det wave and many other factors.

Of course when those are all solved its all just engineering

I'm with you on the X rays, for a U-235 core the obvious option is to try ordinary uranium metal. It ought to behave almost exactly like the real thing (aside from going critical of course). The biggest problem here is you really need very bright, very short pulses of X rays to take pictures. Short of doing the detonation next to a disposable synchotron or a short distance from someone elses successful A bomb, I haven't solved this part yet.

akinmad - 20-4-2006 at 05:18

Quote:

Originally posted by Marvin
The basic science behind the implosive lens is quite simple and given the refractive index of a transparent material n is the ratio of c to the speed of light through it, I'm sure convensional lens making math would give *an* answer.

IIRC, there is a document in LANL set, which describes how a plastic wave shaper shapes the shockwave in a slapper type detonator.

I mean, it seems to me, the weapon designers do not use traditional explosive lenses which are initiated at a single point, but rather than slapper detonators which are capable of initiating large areas, thereby eliminating need for complex lens designs.

Again in the Trigger List I mentioned above there was a section dedicated to slapper detonators. Regards.

Marvin - 20-4-2006 at 16:31

The plane wave capability of slappers seems to be based on large numbers of individual detonators over a surface. The documents suggest half an inch apart, given electrical and size restrictions over implosive lens which is all solved by design, this seems a poorer solution.

If slappers could be produced in a very uniform way and initiated in large numbers, this might be satisfactory for getting a bang.

I can't find anything on waveshapers with slapper in the title.

Chris The Great - 21-4-2006 at 00:39

Yes, lots of detonators will work in place of a spiffy implosion system (they did this for the Trinity test). However, an implosion system will use far less explosive and be much much much smaller. I'd rather desgin something that could possibility be transported to a remote location for getting a "bang".

Organikum - 21-4-2006 at 02:11

Without getting into details about the actual construction of a nuclear weapon: Doesn´t a natural uranium reactor as this canadian design breed plutonium which can be more easily separated then U235? Requiring just natural uranium (maybe slightly enriched which could be done with simpler technology then centrifuge arrays) and heavy water?

The CANDU reactor is in my understanding a breeder able to breed about anything including plutonium. The production of heavy water was discussed here on this board and should be no big obstacle when coupled for example with a large scale electrolytic seawater desalination installment - very low yields compensated by the sheer mass of water processed.

/ORG

PS: I looked this up and it seems that India and Pakistan used heavy water moderated reactors for breeding plutonium for nuclear weapons.

Why does Iran go through the trouble of centrifuge arrays if they just want a nuclear weapon? I believe that Iran is technologically far more advanced then Pakistan is btw.
This is a technical question, please keep politics to the other threads in Whimsy.

[Edited on 21-4-2006 by Organikum]

a_bab - 21-4-2006 at 14:14

Among the first nukes any nuclear country had were the uranium canon type ones. Plutonium is difficult to implode, so I'd go for uranium if I wanted something simple.

On the other hand Iran declaired that they need the uranium for civilian purposes; that may answer your question.

Marvin - 23-4-2006 at 03:20

No.

First nuke detonated ever - plutonium. First nuke the UK had, plutonium. First nuke india had, plutonium.

The complexity of the implosion system is dwarfed by the problem of enriching the uranium. Not even by technical requirements, but sheer scale. Add to that the very poor performance of gun type designs, large fuel requirements, poor yeild, the advantage of uranium vanishes.

Building a reactor just for plutonium is a fairly big event, you'd need in the region of 100 tons of natural enrichement fuel. This is probably the smallest, easiest to hide method. Graphite is probably the way to go too, D2O is expensive and very visible (Needs a high capacity infrastructure). In the long run D2O is far superior of course.

Power reactor on the other hand more or less needs fuel enriched to 3-5% 235 to be cost effective. Iraq had enough of this for 2 research reactors and did nothing with it (Isreal bombed the facilities they were planning to use them in). The problem is a genuine power producing reactor could also make bomb grade plutonium on the side, and would be very difficult to monitor. If you are alowing enrichement to 3 or 5% in the sort of quantity that would fuel a large power plant, this could also be abused to produce weapons feasable material. Its the infrastructure, rather than the threat of the first bomb.

The USA loses track of several bombs worth of plutonium a year. Maybe its being stored by someone for military purposes, maybe it ends up in the buiried waste, maybe it doesnt even exist and is an artifact of essaying errors. But if the USA can't keep tabs on its own plutonium production accuratly, monitoring another country would be impossible.

a_bab - 23-4-2006 at 03:28

Yeah, you are right. My mistake. I was reading about the Pakistan and I guess they had uranium bombs, before they switched to Pu ones.

Marvin - 23-4-2006 at 04:39

After checking a few things, I'm not as right as I thought. US, USSR, UK, India and France all had plutonium bombs first. Pakistan, South africa and China had HEU. China used implosion though, the pakistan is a 'don't know', about the only people to consider gun type seriously were the South Africans, and they never tested it. Isreal was rather more successful in keeping things secret, but seems to be plutonium by the time the world found out.

Certainly the gun type design is a fringe weapon but more countries had the opertunity to use HEU than I'd have thought.

JohnWW - 26-4-2006 at 10:46

Quote:

Originally posted by unionised
(cut) OK it needs more Pu or U but since it's just an academic exercise that doesn't matter. After all if you can get the first kilogram the second one is easy.

Do you know of anyone who sells plutonium, or either enriched or unenriched uranium? Importing the stuff may be difficult - several countries, including New Zealand, ban the importing of plutonium or enriched uranium.

Also, which isotope is the plutonium? - Pu-239 is the most easily made, from spent enriched-uranium fuel rods in which neutrons convert the U-238 to mostly Pu-239, which is that usually used in bombs and reprocessed fuel rods, but Pu-244 is by far the longest-lived and least radioactive isotope, sufficiently to occur in trace amounts in uranium ores.

akinmad - 26-4-2006 at 12:01

Quote:

Originally posted by JohnWW
Also, which isotope is the plutonium? - Pu-239 is the most easily made, from spent enriched-uranium fuel rods in which neutrons convert the U-238 to mostly Pu-239, which is that usually used in bombs and reprocessed fuel rods, but Pu-244 is by far the longest-lived and least radioactive isotope, sufficiently to occur in trace amounts in uranium ores.

Problem with Pu extracted from spent Fuel Rods, is that it is reactor grade plutonium (i.e. it contains a lot of even numbered Pu isotopes), which causes the deviced made with them to fizzle not to detonate.

In order to the make Weapon grade Pu, one has to cook U-238 in the reactor with slower (or more thermalized) neutrons for a period shorter than from an ordinary commercial power reactor. IIRC, Israelis were burning their fuel rods for a period of ca 100 days in the reactor then remove the fuel rods and extract plutonium.

For that reason, IAEA inspectors install seals on the reactor vessels to determine if the fuel rods are removed prematurely. Regards