jmasly@mainz-emh2.army.mil (John Masly) (11/29/90)
From: John Masly <jmasly@mainz-emh2.army.mil> RE: Nuclear vs. Thermonuclear FROM: prm@ecn.purdue.edu >...Inside the fuel capsule is an Oralloy "sparkplug"... FROM: henry@zoo.toronto.edu >...modern U.S. thermonuclear weapons no longer need "sparkplugs' >to ignite the fusion reaction... Lets face it...we're not talking about your normal IC engine. :-) The following is not classified..just ask your local nuclear physicist about it. I'm no physicist, but let me say what I think I know. (Feel free to correct part, or all of what follows) There are two nuclear reactions that result in a blinding flash and a deafening roar: fission and fusion. In fission weapons, you take a lump of naturally radioactive material, and entice it to speed up its natural decay process. Fission occurs when a 'splitter' particle (neutron) strikes the nucleus of a atom, causing it to split into two daughter products, and releasing energy as well as one or more additional 'splitter' particles. The usual (?) practice for a fission device has been to take a quantity of a heavy fissile material (U-235 or Plutonium) just below the material's critical mass, and compress it to the point that it becomes critical. At this point more 'splitter' particles would be causing fission events in the material, than would be lost to the outside environment. Since each fission event produces, on the average, more than one additional 'splitter' particle, the number of fission events taking place in the material rapidly increases. Pretty soon the energy generated by all the fission events 'warms' the environment sufficiently to cause everything in the immediate area to take on a 'certain glow'. (BOOM!) :-) Fusion, on the other hand, is just the opposite. You start with two atoms of some light element (hydrogen), and cause them to collide with sufficient energy so that they stick together (fuse) and form a heavier element. This reaction also releases energy; more energy per event than in a fission reaction. The fuel of choice here is the isotopes of hydrogen known as Deuterium and Tritium. The only problem with these gaseous fuels, is that they do not have sufficient internal energy to fuse at normal temperatures. In order for these isopotes to start to fuse, they must be heated (energy added). This energy must be added to the gas at a rate fast enough to start the fusion process before the gas container melts. The only way I know of producing the energy required to start the fusion reaction, is to start with a fission device (bomb). So I would guess that Oralloy is not a 'sparkplug' at all, but something added to the design to enhance the end result. If you want my guess at what Oralloy is, check out the definition of 'Tritium' in a good dictionary (Webster's 3rd International, for example). (Sorry this took so long.) ***************************************************************** * John R. Masly, Mechanical Engineer, Mainz Army Depot, Germany * * "The U.S. Army's Depot on the Rhein" (German Spelling) * ***************************************************************** ON THIS DAY: 1950 First Marine Division begins fighting retreat to the sea after Chinese forces enter the Korean War.
henry@zoo.toronto.edu (Henry Spencer) (11/30/90)
From: henry@zoo.toronto.edu (Henry Spencer) >From: John Masly <jmasly@mainz-emh2.army.mil> >So I would guess that Oralloy is not a 'sparkplug' at all, but >something added to the design to enhance the end result. If you >want my guess at what Oralloy is, check out the definition of >'Tritium'... Oralloy is bomb-designer slang for U-235; it is short for "Oak Ridge alloy", Oak Ridge being the site of the first US uranium-enrichment plants. There is no secrecy or mystery about this. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry
jmasly@mainz-emh2.army.mil (John Masly) (12/03/90)
From: John Masly <jmasly@mainz-emh2.army.mil> >From: prm@ecn.purdue.edu (Phil Moyer) >Oralloy is a contraction of the phrase "Oak Ridge Alloy". It was coined >in 1945 during the Manhattan project. It was/is the code name and industry >jargon for U-235. Nice try, though. >From: henry@zoo.toronto.edu (Henry Spencer) >Oralloy is bomb-designer slang for U-235; it is short for "Oak Ridge alloy", >Oak Ridge being the site of the first US uranium-enrichment plants. There >is no secrecy or mystery about this. Thanks to both, for explaining the jargon to me. The original phrase that got me started was "thermonuclear weapons no longer need 'sparkplugs' ". Obviously, they do, wheather it is called Oralloy or U-235, or plutonium. To believe otherwise, would be to assume that the national labs (Sandia, LLL, etc.) have found a means to produce fusion without the flash-bang of a fission device, and can fit it all within the size of a bomb casing. You need a lot of energy to start the fusion process, just take a look at the set up they have for trying to produce commercial fusion power. I think 'sparkplugs' will be needed for a long time to come. :-) >From: prm@ecn.purdue.edu (Phil Moyer) >BTW, the Tritium (H-3) in the fusion weapons comes from the fissioning of >Lithium-6 in the ceramic "fuel" in the weapon itself. Tritium has a half life >of 12.xxx years, so is inappropriate for use in thermonuclear weapons (in it's >raw state); much better to produce it as needed. :-) Probably so, since it is alwasy nicer to carry around some 'safe' object that only becomes deadly, when needed. But the choice of the word 'inappropriate' in itself, seems inappropriate. Many nuclear weapons are 'yield selectable'. Meaning that you can take certain actions before you launch/ drop/fire the weapon, to select the size of the blast. These 'select-a-bang' weapons must use some material to enhance the yield, that can be easily added to the basic weapon by the user. Since it is kind of hard to add more solid material to an encased bomb, the only reasonable way I can see of doing this, is to add additional (gaseous) fusionable material to the the device at the proper time (and place) in the nuclear process. Also, nuclear devices receive periodic maintenance just like every other item in the inventory, so if the half-life of H-3 is just 12.xxx years, what would be so inconvienent about replacing the H-3 container on a periodic basis? BTW, what are the decay products of H-3? Isn't one of them Deuterium (H-2)? What is it's half-life? :-)
henry@zoo.toronto.edu (Henry Spencer) (12/04/90)
From: henry@zoo.toronto.edu (Henry Spencer) >From: John Masly <jmasly@mainz-emh2.army.mil> > Thanks to both, for explaining the jargon to me. The original > phrase that got me started was "thermonuclear weapons no longer > need 'sparkplugs' ". Obviously, they do, wheather it is called > Oralloy or U-235, or plutonium. To believe otherwise, would be > to assume that the national labs (Sandia, LLL, etc.) have found > a means to produce fusion without the flash-bang of a fission > device... No, sorry, you missed the original point entirely. The fission explosion used to compress and heat the fusion package is *not* called a "sparkplug". All current fusion bombs do need that one. The question is whether current fusion bombs need a *second* fission assembly, inside the fusion assembly, to actually ignite the fusion reaction. That's what a "sparkplug" is. It is reported that US fusion bombs used to use sparkplugs, but that modern ones do not need them. >>BTW, the Tritium (H-3) in the fusion weapons comes from the fissioning of >>Lithium-6 ... > > ... Many nuclear weapons are 'yield selectable'... > ... Since it is kind of hard to add more solid material to > an encased bomb, the only reasonable way I can see of doing > this, is to add additional (gaseous) fusionable material to the > the device at the proper time (and place) in the nuclear process. Dial-a-yield bombs are reported to function mostly by introducing varying (but small) amounts of tritium into a *fission* core. Most modern fission bombs use a small amount of fusion to "boost" the fission reaction (this should not be confused with the use of a fission explosion to ignite a much larger fusion explosion), and varying the amount of fusion apparently varies the fission yield fairly effectively. Precisely how this carries over into a variable yield in the main fusion reaction of a fusion bomb is less clear, but the obvious possibility is that less energetic heating and compression of the fusion package means less fusion yield (certainly the equivalent is said to be true for fission bombs: getting more energy into the core during the implosion process gives higher fission yield). > Also, nuclear devices receive periodic maintenance just like > every other item in the inventory, so if the half-life of H-3 > is just 12.xxx years, what would be so inconvienent about > replacing the H-3 container on a periodic basis? ... In fact, replacing the tritium in the "booster" charge is said to be a significant part of the periodic-maintenance requirement for nuclear weapons. However, this is a relatively small amount of gas. Using tritium as fusion fuel would require much larger amounts, and it would probably have to be stored as liquid. The first US fusion-bomb test reportedly used liquid deuterium and tritium, and replacement of those by more easily stored materials is said to have been the major step needed to produce a practical weapon. > what are the decay products of H-3? Isn't one of them Deuterium > (H-2)? What is it's half-life? :-) Tritium decays into helium-3, which is stable. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry
karish@mindcraft.com (Chuck Karish) (12/07/90)
From: karish@mindcraft.com (Chuck Karish) In article <1990Dec4.002646.10188@cbnews.att.com> henry@zoo.toronto.edu (Henry Spencer) writes: |The fission explosion |used to compress and heat the fusion package is *not* called a "sparkplug". |All current fusion bombs do need that one. The question is whether current |fusion bombs need a *second* fission assembly, inside the fusion assembly, |to actually ignite the fusion reaction. That's what a "sparkplug" is. It |is reported that US fusion bombs used to use sparkplugs, but that modern |ones do not need them. What about the polonium/beryllium igniters that were used in the first fission bombs? Are they still in use? -- Chuck Karish karish@mindcraft.com Mindcraft, Inc. (415) 323-9000
henry@zoo.toronto.edu (Henry Spencer) (12/09/90)
From: henry@zoo.toronto.edu (Henry Spencer) >From: karish@mindcraft.com (Chuck Karish) >|...reported that US fusion bombs used to use sparkplugs, but that modern >|ones do not need them. > >What about the polonium/beryllium igniters that were used in the >first fission bombs? Are they still in use? It is said that modern fission bombs generally use a different method: a burst of neutrons is fired into the core from outside at the appropriate time. My guess would be that the major advantage is delaying nuclear ignition until a bit later in the implosion process. (How they get the neutrons is no mystery: an electron tube filled with low-density gas will accelerate gas ions into the negative electrode if a high voltage is applied. Make the gas deuterium, use a negative-electrode material containing tritium, and apply a sufficiently high voltage, and you will get a sprinkling of D-T fusion reactions as the ions hit. The result is a spray of neutrons out the end of the tube. Such tubes are used for certain civilian applications, e.g. neutron radiography -- although rumor hath it that the bomb-detonator tubes are specially designed for the job, which is not surprising.) For those who aren't up on this, fissionable materials will ignite spontaneously when compressed into a critical mass, but ignition is more predictable and better yields can be obtained if you give the stuff a positive kick at a well-chosen time. Spontaneous ignition then becomes undesirable, and attention has to be paid to materials and design to prevent it. For example, this is why you don't see the gun-type bomb design used for plutonium, which has a greater tendency to spontaneous ignition than U-235. It's also why building a bomb out of plutonium reprocessed from civilian reactor fuel is a poor idea, because such plutonium will have significant amounts of Pu-240 in addition to the desired Pu-239, and Pu-240 makes spontaneous ignition very likely -- military plutonium-production reactors remove the breeding rods from the reactor relatively early to avoid Pu-240 buildup. If spontaneous ignition occurs early enough, the bomb goes "splut" instead of "boom", blowing itself apart before the fission reaction really gets going. Just in case anyone is getting edgey about this... The above is all published information. See John McPhee's "The Curve Of Binding Energy" and Howard Morland's "The Secret That Exploded" in particular. -- "The average pointer, statistically, |Henry Spencer at U of Toronto Zoology points somewhere in X." -Hugh Redelmeier| henry@zoo.toronto.edu utzoo!henry
bales@ATHENA.MIT.EDU (James W Bales) (12/11/90)
From: bales@ATHENA.MIT.EDU (James W Bales)
henry@zoo.toronto.edu (Henry Spencer) suggests the sources
See John McPhee's "The Curve Of Binding Energy"
and Howard Morland's "The Secret That Exploded"
for information on nuclear triggers. Another source - and an magnificent
book in general - is Rhodes "The Making of the Atomic Bomb. In addition to
being an excellent history of the bomb, it is also a very good primer on
20th century physics for the interested lay person.
Jim Bales bales@athena.mit.eduseeger@thedon.cis.ufl.edu (F. L. Charles Seeger III) (12/11/90)
From: seeger@thedon.cis.ufl.edu (F. L. Charles Seeger III) In article <1990Dec8.223807.29796@cbnews.att.com> henry@zoo.toronto.edu (Henry Spencer) writes: |From: henry@zoo.toronto.edu (Henry Spencer) |>From: karish@mindcraft.com (Chuck Karish) |>What about the polonium/beryllium igniters that were used in the |>first fission bombs? Are they still in use? | |It is said that modern fission bombs generally use a different method: |a burst of neutrons is fired into the core from outside at the appropriate |time. My guess would be that the major advantage is delaying nuclear |ignition until a bit later in the implosion process. Correct, though it is better to describe it as initiating the neutronic phase of the explosion with a large initial neutron population (not just when it starts). This gives the largest possible final neutron population before the bomb 'disassembles'. Of course, the fission yeild will closely correlate with the size of the last generation of neutrons. So, maximizing the number of neutron generations before disassembly, maximizing the excess criticality of the assembly during this neutronic phase, and maximizing the size of the initial neutron population all contribute to an 'efficient' use of the fissile material in the bomb core. |(How they get the neutrons is no mystery: an electron tube filled with |low-density gas will accelerate gas ions into the negative electrode if |a high voltage is applied. Make the gas deuterium, use a negative-electrode |material containing tritium, and apply a sufficiently high voltage, and you |will get a sprinkling of D-T fusion reactions as the ions hit. The result |is a spray of neutrons out the end of the tube. Such tubes are used for |certain civilian applications, e.g. neutron radiography -- although rumor |hath it that the bomb-detonator tubes are specially designed for the job, |which is not surprising.) It is my understanding that the dueterons are actually formed into a beam, and that the neutron burst is accurately timed by sweeping this beam across the tritium target at the 'correct' time. The startup of a gaseous discharge is not sufficiently predictable to give the accurate timing required, so this beam sweeping technique is used. Accurate timing is critical to optimal operation, so extremely stable, accurate and reliable oscillators are necessary for this application. (In another article Henry answered a question about H-3 (tritium) decay, but failed to answer a question about the stability of H-2 (dueterium). Deuterium is stable, though it will undergo a neutron emission reaction if exposed to gamma radiation. The neutrons so generated give a 'minimum' power level to reactors moderated by heavy water. Oh, Henry's answer was correct, i.e. tritium decays to helium-3 by soft beta decay with a 12 year half life, and helium-3 is stable. BTW, tritium has been used in watch dials, in place of radium, which is no longer used.) I believe that these 'neutron triggers' are actually produced at a DOE site run by GE in Pinellas County, Florida (north of St. Petersburg, my hometown, and west of Tampa). Recently, GE has told the U.S. government to find a new operator for this facility, because they are unwilling to accept the legal liabilities for operation of this site that the Feds are trying to foist off on them. GE is giving 18 months notice. Perhaps, similar situations will develop (or already have) at other such sites. Anyway, the local press has published reports in the past that 'significant' amounts of tritium are located on this site. I see this as confirmation of the use of these DT neutron triggers. I have heard some engineers dismiss this possiblity because of the trouble of generating 25 kV or so from batteries within the bomb. I don't have any guesses as to how this is done, but the dueterium nuclei will have to accelerated to a high potential to give a substantial reaction rate with the tritium target. This problem is probably why earlier designs used a beryllium neutron source (beryllium emits a neutron when hit by an alpha particle). Perhaps, the beryllium was isolated from plutonium (or polonium) by paper, which the initial chemical blast would destroy, allowing the alphas to reach the beryllium nuclei. Note that Pu-Be (or similar) nuetron sources are normally used to help bring a reactor up to power. |For those who aren't up on this, fissionable materials will ignite |spontaneously when compressed into a critical mass, but ignition is more |predictable and better yields can be obtained if you give the stuff a |positive kick at a well-chosen time. Spontaneous ignition then becomes |undesirable, and attention has to be paid to materials and design to |prevent it. For example, this is why you don't see the gun-type bomb |design used for plutonium, which has a greater tendency to spontaneous |ignition than U-235. It's also why building a bomb out of plutonium |reprocessed from civilian reactor fuel is a poor idea, because such |plutonium will have significant amounts of Pu-240 in addition to the |desired Pu-239, and Pu-240 makes spontaneous ignition very likely -- |military plutonium-production reactors remove the breeding rods from |the reactor relatively early to avoid Pu-240 buildup. If spontaneous |ignition occurs early enough, the bomb goes "splut" instead of "boom", |blowing itself apart before the fission reaction really gets going. Again, Henry is right, though I could quibble that he should have used the word "fissile" rather than "fissionable". The former refers to isotopes that will undergo fission after absorbing a neutron of any energy, while the latter refers to isotopes that will fission only after absorbing a neutron above a certain energy threshold. (Actually, "fissionable" can refer to both types of nuclei, but it is usually easier to just say "fissionable" rather than "fissionable, but not fissile".) Examples of fissile isotopes are U-233, U-235, U-239, Pu-239 and Pu-241. U-238 is an example of fissionable isotope. U-238 and Thorium-232 are examples of "fertile" isotopes, which can be bred into fissile isotopes. Sorry, if I am being too pendantic. Also, let me expand on Henry's point about Pu-240 contamination of fuel. The problem with Pu-240 is that it has a relatively high probability of decay by spontaneous fission. During detonation this is undesirable because the neutrons so released will tend to lead to early disassembly (and a "splut") by initiating the neutronic phase in an early, slow and far suboptimal manner. Hence, the use of high burnup civilian fuel for extracting Plutonium puts you back in a similar boat that you are with Uranium (i.e. isotope separation). However, the use of low burnup fuel, as Henry points out, largely obviates this problem. This is an interesting non-proliferation issue, in that it implies the need for monitoring of nuclear power plants in third-world countries to prevent diversion. It is also interesting that the Canadian CANDU reactor (based on unenriched Uranium and heavy water) is a proliferation problem because it produces low burnup spent fuel. Concerns over proliferation caused the Carter administration to abandon fuel reprocessing. As Henry suggests, this concern is less persuasive when we are dealing with high burnup fuel with high Pu-240 contents. However, as India showed (reportedly using reprocessed fuel from a CANDU reactor to build their bomb) there is legitimate concern for low burnup fuel reprocessing. Can anyone update us on the CANDU program or other details on this issue? (Also, if my memory fails about the diversion of CANDU fuel by India, please gently correct me.) Before anyone asks, American nuclear power plants generate high burnup spent fuel. (There is a body of opinion that Thorium-232/U-233 breeding is safer from a non-proliferation standpoint than U-238/Pu-239. However, U-233 should be better bomb material than U-235, though not nearly as good as Pu-239. I don't recall enough about the U-233 fuel cycles to state whether there is a situation similar to Pu-240. I would be interested to hear from someone that does, or can take the time to research it.) |Just in case anyone is getting edgey about this... The above is all |published information. See John McPhee's "The Curve Of Binding Energy" |and Howard Morland's "The Secret That Exploded" in particular. Thanks for the pointers to the books, Henry. Chuck -- Charles Seeger E301 CSE Building Office: +1 904 392 1508 CIS Department University of Florida Fax: +1 904 392 1220 seeger@ufl.edu Gainesville, FL 32611-2024
hagerp@iuvax.cs.indiana.edu (Paul Hager) (12/17/90)
From: hagerp@iuvax.cs.indiana.edu (Paul Hager)
Just a short followup to Charles Seeger's comments.
Regarding Th-232/U-233 fuel cycles:
During the INFCE (International Nuclear Fuel Cycle Evaluation) which
was instituted at the behest of the Carter Administration to look
into "proliferation resistant" fuel cycles, a number of different
approaches were investigated. For U/Pu fuel cycles, "spiking" and/or
"denaturing" of the Pu (adding a highly radioactive nuclide or using
high burnup Pu + leaving highly radioactive nuclides in during
reprocessing), among other approaches, were suggested. The idea
was to make the Pu self-protecting from theft or diversion because
of the intense radiation field.
The Th/U fuel cycles were predicated on the idea of advanced thermal
reactor designs that had breeding ratios of 1.0. The idea was that
the initial fissile load would never be augmented. Of course, for
this to work, it would be necessary for radwaste to be removed
continuously (some of it is a neutron poison) and to sequester the
Pa-233 which, if memory serves, has a half-life of 40 days or so
(don't have a nuclide table handy, sorry) until it decays to U-233.
Two candidate systems were the Molten Salt Reactor and the Gas
Core Reactor. The various components of the MSR system were
tested at Oak Ridge in the late '60s through the mid-70s in the
Molten Salt Reactor Program. These tests included laboratory
demonstration of on-line reprocessing (all of this is covered in
the quarterly progress reports). The Gas Core Reactor was more
exotic and would have operated using U-333 hexafloride gas as
the fuel. Again, this is from memory, I seem to recall that
the fissile loading for a Gas Core system would have been about
100 kg of U-233.
The sequestration of the Pa-233 in the breeding process was to
prevent neutron capture and beta decay to U-234, which is a
diluent and not fissile. The U-234 is significant only because
if it is present, it means that U-233 is not -- in other words,
the system would be designed to maximise conversion of Pa-233
produced by neutron capture into U-233 to get the 1.0 breeding
ratio.
Finally, although I'm a real champion of the Th-232/U-233 fuel
cycle, I think the "proliferation resistance" argument is not
a strong one. Ultimately, there are ways around design safeguards
and even high-burnup Pu could be used to make nuclear devices.
Pre-initiation from the neutrons present due to spontaneous
fission decay in Pu-240 is, so far as I know, a "solved-problem"
for sophisticated nuclear weapons technologies.
--
paul hager hagerp@iuvax.cs.indiana.edu
"I would give the Devil benefit of the law for my own safety's sake."
--from _A_Man_for_All_Seasons_ by Robert Bolt