The Lowest-Tech Atom Bomb
by Richard A.
Muller
Technology for
Presidents
October 11,
2002
Saddam Hussein
had us completely fooled, once. Prior to Desert Storm in 1991, we had monitored
and embargoed his importation of high tech centrifuge and laser equipment that
could be used to make highly-enriched uranium (HEU). material that -- once you
have it -- makes building an atomic bomb easy. After Saddam's defeat, inspectors
found that he had spent an estimated $8 billion building calutrons, ancient
devices (from the 1940s) that Ernest O. Lawrence had used to make HEU for the
Hiroshima bomb. (See 'Springtime, Taxes and the Attack on Iraq,' technologyreview.com, Feb. 7, 2002). Nobody had anticipated that Saddam
would use such a low-tech approach.
We won't be
fooled again. U.N. weapons inspectors, if they are ever readmitted to Iraq,
will search specifically for evidence of calutron construction. A calutron is a
magnetic separator that makes HEU by taking raw or partially-purified uranium
and concentrating the rare and more easily fissionable isotope U-235, which
makes up only 0.7% of natural uranium. For a uranium bomb, this separation is
the hard part; the weapon design is easy. According to the International Atomic
Energy Agency, 25 kilograms is a 'significant amount' of HEU -- an amount, they
say, 'in respect of which the possibility of manufacturing a nuclear explosive
cannot be excluded.' If Saddam has this much HEU, he essentially has a nuclear
weapon.
It takes
nearly two tons of uranium ore, run efficiently through calutrons, to separate
25 kilograms of HEU. Most analysts believe it unlikely that Saddam has enriched
this much uranium. When his previous calutrons were discovered and destroyed,
they hadn't even been finished. Thus, he probably doesn't have sufficient
HEU -- yet -- for a nuclear weapon.
Unless he is
using an even lower tech approach: smuggling. In 1996, Swiss police in Zurich
arrested a Turkish national and confiscated 12g of HEU. They determined that
the material had been obtained in either Kazakhstan or Russia. The trail was
hot, and four days later Turkish police arrested the remainder of the smuggling
ring, with 1.2 kilograms of HEU in their possession.
Why
worry? A kilogram is not a significant amount. Even smugglers need a
supplier. Is there reason to think that a substantial quantity of HEU is
available?
Consider what
we learned in Kazakhstan. After the Soviet breakup, a large amount of HEU was
left in the republic. To qualify for the benefits of the 1968 Nuclear Non-Proliferation Treaty, the government of Kazakhstan gave its
stockpile to Russia for dilution and safekeeping in 1995. A year later, much to
their embarrassment, the Kazakhstanis reported the discovery of another
205 kilograms of HEU. It had never been listed as missing, and no one was
looking for it; it just turned up. The bookkeeping of the former Soviet states
makes Enron's accounting look scrupulous. How much more HEU is still out there,
undocumented? Nobody knows. That's why we worry.
If you have
your hands on a few grams of U-235, then Saddam is almost certainly your best
customer. Assuming he had spent $8 billion on calutrons to try to produce 25
kilograms, then his cost was $320 million per kilogram. That is over 12 times
the market value of gem-quality diamonds.
In November
2001, police in Istanbul seized about one kilogram of HEU that smugglers tried
to sell to undercover agents for $750,000. Why were the smugglers asking for so
little? Maybe they didn't know their own worth. Or -- here's a chilling
thought -- maybe there is competition, and it is a buyer's market.
True, the
Turkish police did intercept the HEU. But experience with drug smuggling shows
that we catch only a small fraction of what is smuggled. This suggests that
Saddam might even now have many kilograms. Suppose he has a significant
quantity of HEU -- what could Saddam do? Uranium bombs, unlike the more complex
plutonium bombs, don't require the tricky implosion method, but can employ the
simple, reliable gun method. This is all explained in detail by one of the original
designers of the Hiroshima bomb, Robert Serber, in his book, The Los Alamos
Primer. Serber says that the critical mass for a uranium-tampered bomb is 15
kilograms; the Hiroshima bomb, which used three critical masses, was finished
two years and four months after the Los Alamos laboratory opened. It was
considered so reliable that it was never tested before it was used.
Fortunately
for Saddam, Serber's book gives equations and tricks (such as the use of
neutron-reflecting tampers, or casings) that apparently eluded even Heisenberg,
the leader of Nazi uranium project. What's more, Saddam's designers have
been at work for over a decade, while waiting for their supreme ruler to obtain
the HEU.
But Saddam has
no missiles that could reach the United States. What could he do with a few
small bombs?
Unlike
weapons-grade plutonium, (which is typically contaminated with Pu-240, a
spontaneous neutron emitter), U-235 is difficult to detect without active
probing, as with a thermal neutron source). It emits alpha particles and some
energetic gamma rays, but these can be shielded with lead. This makes HEU
relatively easy to smuggle. The easiest way to get a bomb into the US is
probably in a shipping container. We wouldn't detect it unless we were tipped
off about where to look.
Let's imagine
a bad case. Saddam sets off a bomb in Washington D.C. Unlike the designers of
the Hiroshima and Nagasaki bombs, he derives great pleasure from mass death. Unlike
bin Laden, he takes credit immediately for his terrorism. He announces that he
has additional weapons, and that if the U.S. retaliates, he will start setting
them off in major U.S. cities.
Last month,
British Prime Minister Tony Blair announced that Saddam has been seeking to buy
uranium from African countries (which produce 20 percent of the world
supply). This is, of course, illegal, since he has no reactors, and no
legitimate use for large amounts of uranium. But why would he do this, if he
already had HEU? Doesn't his interest prove that he is, at worst, rebuilding
calutrons?
No. If I were
Saddam, I would import uranium in order to give that impression, to lull the
U.S. into a false sense of security, into believing that there is plenty of
time. Let's not make that same mistake twice -- of assuming that Saddam is doing
it in the obvious way.
What hope have
we? Well, maybe the Kazakhstan case was a fluke, and there is not a significant
quantity of HEU available. Maybe most of the reported smuggling cases were
actually fraud, or CIA sting operations designed to find out who is buying, and
there is no real HEU to purchase. (A widely-reported seizure on September 28 in
Turkey, 250 km from the Iraqi border, contained no real uranium.) Maybe Saddam
has already made a bomb, but hasn't yet figured out how to sneak it into the
U.S. Maybe Serber deliberately put plausible but misleading information
into his book that would foil and delay a terrorist, and make an untested bomb
into a dud.
We can hope.