Thursday, November 20, 2008

Experts: Iran has enough low leverl enriched uranium for nukes

According to experts quoted by the New York Times, Iran has enough enriched Uranium to make a nuclear weapon. This seems to be true and not true. Iran always had enough uranium to make a bomb, if it could be purified. It now has about 630 KG of low enriched uranium. This may be 5% to 20% U-235. According to the IAEA report, we are talking about 5% enriched Uranium. Critical mass for a bomb is about 50 kg of (presumably pure or highly enriched) U-235 according to Wikipeda. In 630 KG of 5% enriched uranium there are only 31.5 KG of enriched Uranium. With 20% enriched uranium, you would require at least 400 KG.
But if a different (implosion) design is used, they might be able to make a bomb with as little as 20 pounds of uranium (less than 10 KG):
However, less widely known is that uranium can be used in the different type of bomb design that was tested in New Mexico and dropped on Nagasaki. This other approach, the implosion design, must be used if the fuel is plutonium. (Because of its differing, more temperamental nuclear properties, plutonium in a gun bomb would predetonate, or fizzle.) An implosion bomb is a much more subtle and delicate thing, harder to construct from scratch than a gun bomb. However, an implosion bomb can indeed be fueled by weapons grade uranium instead of plutonium. Sources estimate that an implosion design U-235 bomb would need only twenty pounds of fuel, instead of forty. This is because the implosion approach assembles a super-critical mass more efficiently. The barrier to WMD implementation has just been cut in half. Not good news. (See here)
And the same source claims:
More sophisticated implosion designs do more than simply collapse a hollow sphere into a solid one. They achieve such a strong and perfectly shaped implosive force that the solid sphere is actually compressed. Compression into a volume as small as one-fourth that of unstressed solid metal has been reported. In other words, the density of the bomb fuel is as much as quadrupled. Because of the physics involved, this higher density requires less total weight of fuel for a large atomic explosion to occur. The degree of reduction in the amount of fuel required by such a compression-implosion device is classified. I make a semi-educated guess that if the bomb quadruples the density, the weight of fuel needed might be cut in half. If so, ten pounds of weapons grade U-235 would achieve a yield of several kilotons, maybe even a dozen - Hiroshima-scale devastation with only one quarter the fuel. Or, viewed differently, four times as numerous an arsenal for the same amount of fuel. Frightening thoughts.
Iran Said to Have Nuclear Fuel for One Weapon
Iran has now produced roughly enough nuclear material to make, with added purification, a single atom bomb, according to nuclear experts analyzing the latest report from global atomic inspectors.
The figures detailing Iran's progress were contained in a routine update on Wednesday from the International Atomic Energy Agency, which has been conducting inspections of the country's main nuclear plant at Natanz. The report concluded that as of early this month, Iran had made 630 kilograms, or about 1,390 pounds, of low-enriched uranium.
Several experts said that was enough for a bomb, but they cautioned that the milestone was mostly symbolic, because Iran would have to take additional steps. Not only would it have to breach its international agreements and kick out the inspectors, but it would also have to further purify the fuel and put it into a warhead design — a technical advance that Western experts are unsure Iran has yet achieved.
"They clearly have enough material for a bomb," said Richard L. Garwin, a top nuclear physicist who helped invent the hydrogen bomb and has advised Washington for decades. "They know how to do the enrichment. Whether they know how to design a bomb, well, that's another matter."
Iran insists that it wants only to fuel reactors for nuclear power. But many Western nations, led by the United States, suspect that its real goal is to gain the ability to make nuclear weapons.
While some Iranian officials have threatened to bar inspectors in the past, the country has made no such moves, and many experts inside the Bush administration and the I.A.E.A. believe it will avoid the risk of attempting "nuclear breakout" until it possessed a larger uranium supply.
Even so, for President-elect Barack Obama, the report underscores the magnitude of the problem that he will inherit Jan. 20: an Iranian nuclear program that has not only solved many technical problems of uranium enrichment, but that can also now credibly claim to possess enough material to make a weapon if negotiations with Europe and the United States break down.
American intelligence agencies have said Iran could make a bomb between 2009 and 2015. A national intelligence estimate made public late last year concluded that around the end of 2003, after long effort, Iran had halted work on an actual weapon. But enriching uranium, and obtaining enough material to build a weapon, is considered the most difficult part of the process.
Siegfried S. Hecker of Stanford University and a former director of the Los Alamos weapons laboratory said the growing size of the Iranian stockpile "underscored that they are marching down the path to developing the nuclear weapons option."
In the report to its board, the atomic agency said Iran's main enrichment plant was now feeding uranium into about 3,800 centrifuges — machines that spin incredibly fast to enrich the element into nuclear fuel. That count is the same as in the agency's last quarterly report, in September. Iran began installing the centrifuges in early 2007. But the new report's total of 630 kilograms — an increase of about 150 — shows that Iran has been making progress in accumulating material to make nuclear fuel.
That uranium has been enriched to the low levels needed to fuel a nuclear reactor. To further purify it to the highly enriched state needed to fuel a nuclear warhead, Iran would have to reconfigure its centrifuges and do a couple months of additional processing, nuclear experts said.
"They have a weapon's worth," Thomas B. Cochran, a senior scientist in the nuclear program of the Natural Resources Defense Council, a private group in Washington that tracks atomic arsenals, said in an interview.
He said the amount was suitable for a relatively advanced implosion-type weapon like the one dropped on Nagasaki. Its core, he added, would be about the size of a grapefruit. He said a cruder design would require about twice as much weapon-grade fuel.
"It's a virtual milestone," Dr. Cochran said of Iran's stockpile. It is not an imminent threat, he added, because the further technical work to make fuel for a bomb would tip off inspectors, the United States and other powers about "where they're going."
The agency's report made no mention of the possible military implications of the size of Iran's stockpile. And some experts said the milestone was still months away. In an analysis of the I.A.E.A. report, the Institute for Science and International Security, a private group in Washington, estimated that Iran had not yet reached the mark but would "within a few months." It added that other analysts estimated it might take as much as a year.
Whatever the exact date, it added, "Iran is progressing" toward the ability to quickly make enough weapon-grade uranium for a warhead.
Peter D. Zimmerman, a physicist and former United States government arms scientist, cautioned that the Iranian stockpile fell slightly short of what international officials conservatively estimate as the minimum threatening amount of nuclear fuel. "They're very close," he said of the Iranians in an interview. "If it isn't tomorrow, it's soon," probably a matter of months.
In its report, the I.A.E.A., which is based in Vienna, said Iran was working hard to roughly double its number of operating centrifuges.
A senior European diplomat close to the agency said Iran might have 6,000 centrifuges enriching uranium by the end of the year. The report also said Iran had said it intended to start installing another group of 3,000 centrifuges early next year.
The atomic energy agency said Iran was continuing to evade questions about its suspected work on nuclear warheads. In a separate report released Wednesday, the agency said, as expected, that it had found ambiguous traces of uranium at a suspected Syrian reactor site bombed by Israel last year.
"While it cannot be excluded that the building in question was intended for non-nuclear use," the report said, the building's features "along with the connectivity of the site to adequate pumping capacity of cooling water, are similar to what may be found in connection with a reactor site." Syria has said the uranium came from Israeli bombs.

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