Reactor-Grade Plutonium Can be Used to Make Powerful and Reliable Nuclear Weapons by Richard Garwin

[bananas]

I see this subject coming up on various blogs.
The issue was settled long ago.
Here's something Richard Garwin wrote twelve years ago.
Note that he mentions John Holdren, who is currently Obama's science advisor.

http://www.fas.org/rlg/980826-pu.htm

August 26, 1998

Reactor-Grade Plutonium Can be Used to Make Powerful and
Reliable Nuclear Weapons: Separated plutonium in the fuel
cycle must be protected as if it were nuclear weapons.

by

Richard L. Garwin(1)
Senior Fellow for Science and Technology
Council on Foreign Relations, New York
Draft of August 26, 1998
FAX: [phone]; Email: rlg2 at watson.ibm.com


As access to technology advances throughout the world, the
barrier to the acquisition of nuclear weapons by terrorists
or nations is more and more the barrier to weapon-usable
fissionable material-- traditionally high-enriched uranium
or "weapon-grade" plutonium. Even a modest nuclear weapon
delivered by aircraft, missile, ship, or truck can threaten
the lives of 100,000 people. Therefore it is important to
understand whether reactor-grade plutonium from the nuclear
fuel cycle-- typically 65% fissile (by thermal neutrons)
compared with 93% fissile for weapon-grade material-- can
readily be used to create nuclear weapons. Unfortunately,
the answer is that it can be so used. The conclusion,
therefore, is that separated reactor-grade plutonium must be
guarded in just the same way as if it were weapon-grade
plutonium if it is not to contribute greatly to the spread
and possible use of nuclear weaponry.

<snip>

These facts are interpreted by various bodies as follows:

Mark 1993:
"The difficulties of developing an effective design of the
most straightforward type are not appreciably greater with
reactor-grade plutonium than those that have to be met for
the use of weapons-grade plutonium."

CISAC(3) 1994:
"In short, it would be quite possible for a potential
proliferator to make a nuclear explosive from reactor-grade
plutonium using a simple design that would be assured of
having a yield in the range of one to a few kilotons, and
more using an advanced design. Theft of separated plutonium
whether weapons-grade or reactor-grade, would pose a grave
security risk."

American Nuclear Society Special Panel Report(4) 1995:
"We are aware that a number of well-qualified scientists in
countries that have not developed nuclear weapons question
the weapons-usability of reactor-grade plutonium. While
recognizing that explosives have been produced from this
material, many believe that this is a feat that can be
accomplished only by an advanced nuclear- weapon state such
as the United States. This is not the case. Any nation or
group capable of making a nuclear explosive from weapons-
grade plutonium must be considered capable of making one
from reactor- grade plutonium."

U.S. Department of Energy(5) 1997:
"Proliferating states using designs of intermediate
sophistication could produce weapons with assured yields
substantially higher than the kiloton-range made possible
with a simple, first- generation nuclear device." and

"The disadvantage of reactor-grade plutonium is not so much
in the effectiveness of the nuclear weapons that can be made
from it as in the increased complexity in designing,
fabricating, and handling them. The possibility that either
a state or a sub-national group would choose to use
reactor-grade plutonium, should sufficient stocks of
weapon-grade plutonium not be readily available, cannot be
discounted. In short, reactor-grade plutonium is
weapons-usable, whether by unsophisticated proliferators or
by advanced nuclear weapon states. Theft of separated
plutonium, whether weapons-grade or reactor-grade, would
pose a grave security risk."

As an author of the 1994 CISAC report, I helped formulate
the statement that I quote above. What should the reader
believe? Individuals are often skeptical of official
statements, and it is often said "Those who know, don't
speak; and those who speak, don't know." But that is not
the case with the members of CISAC, all of whom endorsed
this statement; they both know and speak. It is
particularly to be noted that among the Committee are the
following physicists who are knowledgeable about nuclear
weapons and who reviewed a secret study done for CISAC by
the Los Alamos National Laboratory and the Lawrence
Livermore National Laboratory-- the United States' two
nuclear weapon design laboratories. Besides myself, these
include John P. Holdren, Michael M. May, and W.K.H.
Panofsky. May is a former director of the Lawrence
Livermore National Laboratory.

<snip>

[leveymg]

1. Plutonium bombs are devilishly tricky things to get right, even with weapons grade materials

The design and fabrication would have to be expert, and the fusing, timers and trigger circuits of excellent quality. Yes, the scientists at Sandia National Labs could do it, but that doesn't mean that some small, unsophisticated program operating in isolation and secrecy in a third-world country could.

This is old Iraq WMD threat garbage, dredged up by the nuke Iran types.

[caraher]

2. They are tricky, but we should still keep a close eye on plutonium

I agree that "subnational" groups can't pull off building fission bombs, but having the plutonium on hand does lower the bar considerably for countries that might decide to pursue a bomb. And plutonium would be a dandy thing to have for terrorists working on a dirty bomb - whose impact probably lies less in its actual killing capability than the panic it would cause (and who hasn't been heard, true or not, the claim that plutonium is the deadliest substance known to man?).

[bananas]

3. No, this isn't old Iraq WMD threat garbage, and I'm not a nuke Iran type.

Obama is going to try to strengthen the NPT and negotiate arms reductions, it's what he won the Nobel Peace Prize for. These are serious issues which will be an ongoing problem with nuclear energy.

[leveymg]

5. It does date from '98, a time when there was a proliferation of reports of

dubious quality about the alleged link between Iraq and terrorist groups, including al Qaeda, with nuclear ambitions. This was also a period when outright fabrications were appearing, including the emergence of Curveball and other disinformation operatives.

I didn't mean to imply that you, yourself, are a nuke Iran type. I'm saying that these scare stories and fabrications are reemerging in a familiar drum beat by those who now want us to knock off Iran. My apologies - I could use another cup of coffee.

[bananas]

10. I don't think anyone would consider Garwin a war-mongerer or someone who uses scare tactics

If anything, they would say he's the opposite of that, a peace-monger who uses boring facts. This wasn't a scare story or fabrication. In 1997, DOE released some information about some classified material, there was a lot of specultion about it, Garwin was responding to that.

I didn't post this because of anything going on with Iran, this doesn't even apply to the situation with Iran, I posted it because there are nuclear energy proponents who are pollyanna's about the problem of nuclear proliferation.

There are some people who are pollyanna's about nuclear energy and nuclear weapons. Some are pollyanna's about both, they think both nuclear energy and nuclear weapons are wonderful and completely problem-free, they say that nuclear weapons ended WWII and saved millions of lives, they say that MAD worked flawlessly, some of them say that we should use wonderful nuclear bunker busters on Iran's facilities, others say that Iran should have its own nuclear weapons because MAD worked so wonderful between the US and USSR it should work the same wonderful way between Iran and the US, the nuclear genie is out of the bottle, just like there were no gunfights in the old west because everybody carried a sidearm, there will never be wars if every country is armed with nuclear weapons.

Other pollyanna's think nuclear energy is wonderful but not nuclear weapons, they think that no-one could ever want to use nuclear weapons, well maybe only Bush and Cheney, but there will never be anyone else anywhere who would ever consider using nuclear weapons ever again, and besides it's really hard to make nuclear weapons, only geniuses like Einstein could figure out how to do it.

Then there are people like Garwin, and Holdren, and Obama, who are opposed to using nuclear weapons, and are in favor of steep nuclear arms reductions globally, and who are not opposed to nuclear energy, but are aware of its proliferation risks and want to strengthen the NPT to reduce those risks.

It was the UN inspectors and people like Joe Wilson who spoke out against the fabrications of Bush and the neocons. The problem with Iran is over enrichment, the solution is increased oversight by strengthening the NPT, that will also make it harder for people like Bush and the neocons to fabricate evidence.

[bananas]

4. The context is nuclear energy in general

One of the many problems with nuclear energy is the risk of proliferation.
The way some nuclear proponents address this problem is by pretending it doesn't exist.
They ignore the fact that proliferation has been limited by intrusive IAEA inspections, covert monitoring by deep cover agents like Valerie Plame, etc etc.
For more context see http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=102&topic_id=4282126&mesg_id=4282990
and http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=102&topic_id=4282126&mesg_id=4283008

[krispos42]

7. Can a gun-type bomb be made, or do you have to use the implosion type? n/t

[leveymg]

8. Gun-type only works with Highly Enriched Uranium

The original Hiroshima bomb was a gun-type, and it's designers were so certain it would work they didn't even live test it.

The Trinity/Nagasaki devices were Plutonium bombs. This type requires that a sphere of carefully fabricated milled plutonium plates be simultaneously compressed by an explosive shock wave into a core of specific density to achieve critical mass. These bombs are lighter and more compact than HEU bombs, making them easier to deliver by aircraft or missile. The North Korean device tested in 2006 was a plutonium bomb, and it "fizzled" with a yield of .2 to 1 kt. See, http://www.johnstonsarchive.net/nuclear/dprk-ntest.html

[krispos42]

9. I wasn't sure about that.

I remembered that one of the bombs dropped on Japan was a gun-type but didn't know which material it used, and if the material mattered.

Thanks! :hi:

[Tesha]

11. It's a question of how fast the reaction proceeds versus self-disassembly.

Once the nuclear reaction begins, the neutron flux begins to
double and double again and so on. Each doubling of the
neutron flux is referred to as a "shake".

In a plutonium weapon, each "shake" takes about ten nano-
seconds (ten billionths of a second). Full burn-up of the
fuel is usually assumed to take 80 shakes or so so about
0.8 microseconds.

Meanwhile, the explosive energy evolving from the weapon
is busily trying to destroy everything including the weapon
itself. So the weapon has to hold together well enough to
allow the 80 shakes to take place before the whole thing
blasts apart.

In a gun-type device, the mechanical assembly of the two or
three parts of the core's critical mass is quite slow, and with
the rapid doubling of neutron flux that takes place in a
plutonium core, the core "self-disassembles" long before
you can really get the several parts of the core really well
assembled into a single critical mass. The end result is
that the weapon fizzles rather than really explodes.

By comparison, "shakes" in a Highly-Enriched Uranium core
are much slower. This makes it easy for the core to be just
about fully-assembled before enough flux doublings occur
to destroy the core.

Spontaneous fissioning also has an effect on all of this. If
your HEU has very little U-234 contaminating it, there aren't
too many spontaneous fissionings that take place and the
reaction doesn't really get rolling until a specific neutron-
generator (the initiator) is deliberately fired, producing a
sudden flood of neutrons that kicks things off.

I'm not sure about this, but I *THINK* the rate of spontaneous
fissioning in Pu239 is much higher, again making it hard to
assemble a gun-type core fast enough to prevent a fizzle.

And of course, compared to the gun-type device, the implosion
core "assembles" the critical mass much, much faster and in a
geometrically more-favorable shape for complete fissioning
of the fissile material.

Now, shall we discuss tritium "boosting" of the weapon? ;)

Tesha

[krispos42]

12. I can deduce from this, then...

...that plutonium either

a) is denser than U-235, so the neutrons travel to the ajoining nuclei sooner;
b) releases neutrons that travel faster than those from U-235
c) releases more neutrons per fission event than U-235, thus causing more subsequent fission events for the same period of time.
d) some combination of the above


How am I doing? :-)

[Tesha]

13. I honestly don't know the answer to that question!

Yes, "mean free path" (roughly, your suggestion of "density"
has a significant effect; how far can our free neutrons go
before they strike another fissionable nucleus.

But I *THINK* the big handwave is that the half-life* of Pu240
(Pu239 plus that extra neutron we've injected) is very much
shorter than the half-life of U236 (U235 plus that extra neutron).

But in fact, I don't think physicists can explain yet exactly
why radioactive decay takes place** so can't exactly explain
why a given isotope has a certain half-life.

And if someone else knows better, I'm certainly ready to be
further educated! ;)

Atlant


* Half-life = the time in which half the atoms of a given isotope
spontaneously decay. (You probably knew that; I mention it only
"for completeness".)

** And they surely can' tell you *WHEN* it occurs; as far as we
know, that's still one of the truly-random things that happens
in our universe.

[Statistical]

15. See #14 below.

[Statistical]

14. Close.

It has to do with something called spontaneous fission.

When isotopes decay usually they simply release energy but occasionally (well actually very rarely) a spontaneous fission can occur instead. Yeah that is right a small amount of fission is happening right now in natural uranium all over the world.

It is this spontaneous fission that "stars" a nuclear detonation in a critical mass.
Fission releases neutrons which in turn fission other atoms which release neutrons..... etc
However where does the first neutron come from? Spontaneous fission. Without spontaneous fission there would be nothing to "start" the chain reaction.

http://en.wikipedia.org/wiki/Spontaneous_fission

The problem with plutonium is that it has an extremely high rate of Spontaneous fission

First column is half-life, second is likelihood of SF (notice it is very rare), third is number of neutrons per fission, and last is the key state "neutrons per gram per second" (n/gs)

U-235 7.04x108 years 7.0E-11 1.86 0.00001
U-238 4.47x109 years 5.4E-7 2.07 0.0136
Pu-239 2.41x104 years 4.4E-12 2.16 0.022
Pu-240 6569 years 5.0E-8 2.21 920

Weapons grade uranium is 20%+ U-235 and rest U-238. So the n/gs is a combination of the two values depending on exact level of enrichment. Weapons plutonium is Pu-239. Pu-240 is very dangerous due to the high level of SF (notice it is about 50,000x any other isotope). Pu-240 is essentially a contaminant. It has no use or value in weapons. Plutonium is refined until at least 93% Pu-239 (7% Pu-240). That is pretty much the limits of isotope separation. Still even at such a high level of refinement you have a substantial amount of Pu-240. Even at 93% refinement the plutonium core generates roughly 6000x as many neutrons per second than uranium core does.

This means a Plutonium core is "faster". In that brief instance between sub critical and super critical the core will generate a lot of neutrons and as a result thermal energy. The fission rate is not fast enough for nuclear detonation but it is producing a lot of heat as neutrons heat up material when they strike it.

A gun type device is slow. An explosive accelerates the two half-cores towards each other (in some designs only one half-core moves). At about 10 inches apart the mass goes from sub critical to critical thermal energy begins to build up inside the bomb much faster than it can dissipate. Now explosives are pushing the cores very fast but it will still take about 0.3 seconds for the two halves to go from 10" apart to 0" inches apart and become super critical.

For uranium that isn't a problem however for plutonium that 0.3 seconds is an eternity. The plutonium cores generate thermal energy too fast for the bomb to disipate (cool) and the bomb will blow apart before the cores become super-critical.

In an implosion device the speed at which the core compresses is faster and the distance it needs to "move" before becoming super critical is much less. Thus the extra energy from SF isn't enough to destroy the device before going super-critical.

In essence an implosion device detonates "too fast" for the higher rate of SF in Plutonium to be a problem.

Gun-type devices are obsolete and have no advantage over implosion devices other than they are easier to make.

[damyank913]

6. Well so long as they're reliable...