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By David Albright and Mark Hibbs

Bulletin of the Atomic Scientists, Vol. 47, No. 7

September 1991


The high-stakes shell game Iraq has played with its clandestine nuclearprogram is coming to an end. While not all information has been gathered by a U.N. Special Commission responsible for finding and eliminating Iraq's nuclear weapons capabilities, officials involved in the effort are confident there will be no surprises as great as those of the last few months-especially the revelation that Iraq may have been as close as a few years from possession of nuclear weapons.

Six months ago, after the Pentagon ordered the destruction of Iraq' s nuclear infrastructure, President George Bush said, "Our pinpoint attacks have put Saddam Hussein out of the nuclear bomb-building business for a long time to come." In an article published in the Bulletin last March, we questioned whether bombing could accomplish that goal, since we believed that Iraq's nuclear program had been hindered by export controls and by considerable lack of expertise. We also surmised that it would take Iraq a year to build a single nuclear weapon, and a number of years to produce--in a gas centrifuge plant--the highly enriched uranium necessary to build a small nuclear arsenal.

In spring, a defecting Iraqi expert revealed that Iraq, using a technology discarded by the United States for weapons purposes in 1945, may have been able to produce significant quantities of highly enriched uranium within two or three years.

But the new revelations were apparently not alarming enough for Washington's purposes. In June and July, when the extent of Iraq's secret program became apparent, U.S. officials-who had hyped up Iraq's nuclear program to justify the allied offensive in January-again leaked inflated estimates of Iraqi nuclear prowess to eager journalists, whose front-page stories tested the waters for another effort to oust Iraqi dictator Saddam Hussein.

The admission

After a confrontation with U.N. inspectors in Iraq in late June and a diplomatic showdown at the U.N. Security Council July 5, Iraq admitted that it had been working on three clandestine, parallel programs to enrich uranium. The 30-page document Iraq submitted to the Security Council July 7 contradicted denials top Iraqi officials had been making just days earlier.

Iraq insisted in the July 7 report that it had not violated the Non-Proliferation Treaty (NPT), claiming that the programs were for civilian purposes. But the report acknowledged that Iraq had secretly produced uranium oxide and had enriched some uranium. NPT signatory states that do not have nuclear weapons--Iraq is in this category--are required to report such materials to the International Atomic Energy Agency (IAEA). The IAEA Board of Governors voted July 18 to condemn Iraq for violating the NPT and Iraq's safeguards agreement with the agency.

The July 7 report included vague descriptions of Iraq's nuclear activities and lists of equipment and components. It was inaccurate and incomplete. After the U.S. government asked for clarification, Baghdad officials provided more information. Washington remained skeptical and expected more disclosures before July 25, the deadline for Iraq to fully reveal its nuclear program under U.N. Resolution 687 (after the deadline for this issue of the Bulletin).

U.S. officials are now certain that Iraq concentrated its enrichment effort on calutrons--an old, expensive, energy-intensive technology. The United States developed calutrons, or electromagnetic isotope separators, during World War II to make the highly enriched uranium for the atomic bomb that destroyed Hiroshima. Iraq had also been developing gas centrifuge and chemical enrichment technologies [see "Other Paths," page 211, but these efforts had been progressing more slowly than the calutron program, most officials say now.

The defector

Ironically, the United States may have gotten its first hint that Iraq was engaged in a calutron program after Western hostages were released last December. According to one official, particles removed from hostages who had been held near nuclear sites gave evidence of calutron activity. This information was not considered conclusive, however, until more direct information about the program became available.

The surprises began unfolding in the spring, with reports that an Iraqi defector had revealed to U.S. authorities details of an extensive Iraqi program to enrich uranium. The defector was a young electrical engineer who had been trained abroad but returned to Iraq in May 1990 to try to bring his family out of the country. Instead, he was pressed into service in the secret nuclear program.

The defector told U.S. authorities for the first time about the calutron program Iraq had mounted in the 1980s, unknown to U.S. intelligence. The defector was not specifically trained in calutron technology, although he was trained in some specialized areas applicable to a calutron program. Much of his testimony is thought to be credible because he was, according to one official, familiar with "a lot" of the calutron sites.

According to what U.S. officials learned from the defector, Iraq devoted significant resources to its calutron effort, perhaps most of the several billion dollars U.S. experts now believe Iraq may have spent on its nuclear program during the 1980s. The defector also reported, however, that Iraq's calutron effort "lacked depth" in skilled personnel.

Iraq acknowledged in its July 7 report that it had eight operable calutrons "set up for scientific and technical experiments, seventeen separators being set up, and five separators fabricated and being set up." One U.S. official said that Iraq intended to set up several hundred calutrons. But he said that Iraq had not yet crossed the threshold from research and development into large-scale production.

Media reports have alleged that the defector said that Iraq had secretly produced 40 kilograms of highly enriched uranium using calutrons [see "Bomb Hype II," below]. But U.S. officials familiar with the testimony of the defector question the credibility of these statements. According to one official, the defector had "no first-hand knowledge" of the amount of enriched uranium Iraq's calutrons could have produced. He likened the defector to an auto assembly-line worker who installs one component but he the car can go 150 miles per hour.

In mid-July, U.N. inspectors arrived at a "best estimate" of how much highly enriched uranium Iraq could have produced: at most three kilograms. According to one U.S. official, an earlier intelligence estimate-leaked to the New York Times and the Washington Post-that Iraq's calutrons had produced about 12 kilograms of weapon-grade uranium was a "severe worst-case scenario" derived from assumptions for which there was no supporting evidence. One assumption was that Iraq had begun producing highly enriched uranium very soon after it began work on calutrons in the 1980s. Another was that the calutrons in Iraq were far more capable than technical experts at U.S. national laboratories believe they could have been, based on what they know about calutrons and the Iraqi program.

The inspectors

But other parts of the defector's supposed testimony have been easier to confirm-that pilot work was carried out at the Tuwaitha nuclear research center, south of Baghdad, and that Tarmiya, 60 kilometers north of Baghdad, was intended as a large-scale production site. These sites were inspected in May and again in June.

Inspectors at Tuwaitha, which had been heavily bombed, found the remains of Iraq's safeguarded, known nuclear program, but they also found that all the equipment and plant records had been removed from two nearby buildings. One of the buildings had been completely razed and the other largely dismantled.

In June they found calutron equipment and reported to the Security Council in a July 11 confidential memo that they believed Iraq had facilities to operate as many as 5-10 calutrons at the site. According to a confidential U.N. inspection report, "Iraqi declared evidence" shows that Tuwaitha also hosted research and development of ion sources, magnets, and special insulators for high-voltage equipment. [See "Making and Running Calutrons, " pages 18-19.]

Their estimate that Iraq might have produced as much as three kilograms of enriched uranium was based on a supposition that calutrons at Tuwaitha had operated continuously, at a very high rate of output, for at least two years before the Gulf War.

At Tarmiya, inspectors found that electrical and ventilation equipment had been ripped out of buildings, and building materials had been moved about by bulldozers. They found "clear indications" that the facility was to be dedicated to uranium enrichment. Inspectors noted a mix of buildings with unusually large electrical power supplies, one over 100 megawatts and a similar building with about 40 megawatts. Nearby were large chemical processing buildings. They found cranes for disassembling calutrons, large cooling systems, and building layouts appropriate for calutrons.The larger calutron building was believed to have been designed to hold up to 100 calutrons, intended for an initial uranium enrichment stage. A smaller building would have had 20 calutrons for completing the enrichment. According to one U.S. official, Tarmiya, when fully operational, might have produced as much as 20 kilograms of highly enriched uranium a year.

The inspectors estimated in their confidential report that the facilities had been about 6-18 months from being operational before the bombing. They have been "rendered non-operational and may be adequately monitored by periodic inspections," according to this report. Inspectors later said that about 30 calutrons had been located at Tarmiya, and had been test operated. According to senior IAEA officials, Iraq acknowledged having produced one-half kilogram of 4 percent enriched uranium at Tarmiya in these calutrons. U.S. officials believe the numbers may be higher.

On July 15, inspectors found another calutron production facility, nearly identical to the Tarmiya complex, at Al Sharqat, located about 200 kilometers north of Baghdad, between Tikrit and Mosul. One U.S. official doubted that Iraq had other calutron production sites. But other calutron-related sites existed, such as a facility near Mosul, which a U.S. official said was to produce uranium tetrachloride feed material. The inspectors also visited two suspected calutron equipment-manufacturing facilities at Zaafarniyah, 300 kilometers southeast of Baghdad.

Rumors about nuclear activities in northern Iraq abounded long before the Gulf War. Late last year speculation ranged from gas centrifuge enrichment plants in the region, to uranium hexafluoride conversion plants, uranium mines, and-after the war began-an underground reactor to produce plutonium. None of these have been confirmed.

Before and after the allied bombing campaign, Iraq moved some of its key calutron equipment to secret storage sites. After the war, tipped off by U.S. intelligence, U.N. inspectors paid a visit on June 23 to the Abu Gharaib military barracks north of Baghdad. For three days the Iraqis denied the inspectors access to the site-while they moved calutron equipment, believed to have been taken from Tarmiya, away from the site. When they finally admitted the inspectors on June 26, no calutron equipment was to be seen.

On June 28 the inspectors paid another unannounced visit, this time to Fallujah, near Baghdad, before any equipment could be moved. Once again they were denied access. Inspectors climbed atop a 30-meter water tower outside the facility and filmed a convoy of 60-80 trucks slowly leaving the site. Inspectors pursued the convoy in a jeep, approached it, and filmed calutron equipment visible in the trucks. The Iraqis then fired warning shots over the heads of the inspectors, who got the message and backed off.


Iraq's calutron program is alarming to U.N. and U.S. officials not only because it was so well hidden but also because calutron technology is so accessible. A great deal of information about this technology, electromagnetic isotope separation, was declassified after World War II. The United States concluded that calutrons were a dead end, and there was little reason to keep the technology under wraps.

Not only is information freely available, but calutrons are also easier to build than equipment for other, more advanced enrichment technologies such as those based on gaseous diffusion or gas centrifuges. The U.S. government never controlled export of specific calutron components, as it did for other enrichment technologies.

At the same time, however, electromagnetic isotope separation technology presents several major challenges that are not easily overcome. An early problem with calutrons, for example, was that ion source components such as iron, nickel, chromium, and copper could partially vaporize and create unwanted beams that literally cut the operating equipment to pieces.

Ernest 0. Lawrence invented the calutron electromagnetic isotope separator at the University of California in the early 1940s. It was based on the cyclotron; the name is a shortening of "California University cyclotron. " The calutron separates the rare, fissile 235 isotope of uranium from the more plentiful, non-fissile uranium 238 by injecting an ionized beam of high-energy uranium atoms into a large magnetic field (see illustration). Because the two isotopes have different masses, they follow slightly different trajectories, and a collector in the right position will theoretically admit only uranium 235. But the beams are imperfect, so some uranium 238 becomes mixed with the uranium 235.

Little uranium 235 ends up in the uranium 238 collector, however, which means that the extremely "depleted" uranium from this collector can be a telltale signature of calutron activity. U.N. inspectors have collected many samples of soil and material near the suspected Iraqi calutron sites, looking for this evidence, which would lend proof that Iraq has enriched uranium. U.S. officials would not say whether the particles they removed from Western hostages in December revealed this signature.

During World War II, the Manhattan Project spent the equivalent of about $5 billion in 1990 dollars to build a calutron production installation at the Y-12 plant at Oak Ridge, Tennessee. In 1944, the plant began producing the highly enriched uranium used in the bomb dropped on Hiroshima. At its peak in 1945, the program employed nearly 25,000 people and had over 1, 100 separating units in nine buildings. Eight electrical substations at Oak Ridge used more electricity than Canada produced during World War II.

The plant had two types of calutrons. The larger "alpha" units enriched natural uranium to 10-30 percent uranium 235; the smaller "beta" calutrons enriched this product further, up to about 90 percent, for use in weapons. The calutrons were connected into "racetracks" of about 100 units to use the magnets and power supplies more efficiently.

A small number of these calutrons were used after the war to purify stable isotopes for medical purposes and scientific research, but the technology was abandoned for making weapons material because it was extremely slow and costly and required enormous quantities of electrical energy. Still, U.S. government scientists worried that the technology might spread. A report issued by Los Alamos National Laboratory in 1982 suggested that a country with lots of cash, excess electrical energy, and a large labor pool might find the technology attractive. The report listed 20 countries that had researched calutrons, mostly small-scale work for civilian purposes. The list did not include Iraq.

According to an enrichment expert, there have been "no major breakthroughs" on calutrons since the Manhattan Project. Technology has improved incrementally, but not enough to dramatically increase the output of production-scale calutrons.

A successful calutron program would require considerable expertise. According to an enrichment expert, a "fair amount of art" has not been made public about building and operating calutrons, and this would have to be learned by experience if the machines were to work properly.

Today, a typical calutron costing over $1 million might produce several hundred milligrams of uranium 235 a day, although this amount could vary greatly depending on its design and its power source or whether enriched uranium is used as "feed" into the calutron. An enrichment expert said that 5-10 calutrons might be enough for a pilot operation which would be followed by a plant using 50-100 units. A plant designed to produce 50 kilograms a year of uranium enriched to 80-90 percent uranium 235, with two to six ion sources in each calutron producing a usable beam current of 150-600 milliamperes at the collectors, might need 225-900 units. If a large supply of low-enriched uranium is available from other sources, output of highly enriched uranium can be increased fourfold or more. The output of Iraqi production calutrons was not known at press time, although an enrichment expert believes Iraq would have a "tough time" operating calutrons at the upper end of the current range.

Experts say one of the technology's biggest disadvantages is the large amount of energy it requires to power the beams and the magnets. A distinguishing feature of a calutron building is the large power requirement per square foot of floor space. For example, a plant designed to produce 50 kilograms of highly enriched uranium a year would require well over 50 megawatts of electrical power. Since most of this energy turns into heat, calutrons require extensive cooling. The large amounts of heat they discharge to their surroundings may provide a way to detect clandestine facilities through infrared detection devices. This may also suggest a reason intelligence failed to detect Iraq's program before the Gulf War started: large-scale production had not begun.

Calutrons are not very efficient; about 90 percent of the uranium introduced into the unit does not enter the collectors but ends up on the inside of the machine. This uranium must be recovered, particularly in a calutron that starts with valuable partially enriched uranium, entailing a very messy process. A typical operating cycle might be 40 days of continuous operation, followed by a week of maintenance. During this period, the vacuum chamber, which typically can weigh about 10 tons, would be removed with a crane, taken apart, and scrubbed with nitric acid. Collectors and special liners would be sent to a chemical processing area to recover the uranium.

Putting it together

According to the inspection report, there is "documented evidence" that Iraq could manufacture all key components for calutrons, although scientists at U.S. national laboratories are skeptical that Iraq could have supplied all components for the calutron program on its own.

In any case, mastering calutron technology becomes easier if a country has access to high voltage, regulated, direct-current power supplies; modern ion sources; special insulators; and machining technologies and equipment to produce the uranium collectors. The United States does not explicitly control exports of these items.

Iraq may have exploited this loophole when it purchased sophisticated power supplies from Hipotronics of Brewster, New York. In 1990, Iraq received four 45-kilovolt direct-current power supplies rated at 5 amps which might have accelerated several ion beams in a single calutron. Power supplies are large devices that convert alternating-current power to direct current, and increase the voltage as well.

U.S. Customs approved the export of the items without any review. Because the power supplies used vacuum tubes, not modern electronic components, they would have been relatively easy to duplicate, assuming Iraq could have imported or made vacuum tubes and other electronic equipment. Hipotronics officials pointed out, however, that the voltage regulators on the equipment they exported to Iraq would not have been precise enough for calutrons; Iraq would need to get better regulators from another source.

Iraq also tried to buy 27 large-throat vacuum diffusion pumps from CVC Products, Inc. in Rochester, New York, in 1989, but U.S. Customs became suspicious about the pumps' ultimate use and seized the shipment. Experts speculated at the time that the pumps might have been for an enrichment program, but it now seems likely that they were explicitly for calutrons. U.S. export officials are now considering establishing more controls on the equipment used in calutrons. Sophisticated high-energy power supplies, insulators, and large vacuum pumps are likely candidates for control.

What else is new

The new information about Iraq's plans to make enriched uranium is by far the most significant development since our article in the March 1991 Bulletin went to press. But certain other facts have come to light as well that may relate to Iraq's capability to make nuclear weapons.

Recent revelations have focused attention on the enrichment programs. As of mid-July, no new public information about Iraqs capability to actually make a deliverable nuclear weapon using highly enriched uranium had been revealed, although the U.N. inspectors were just beginning to look for indications of such an effort. Everyone agrees that the amount of fissile material Iraq possesses under internal safeguards would be enough for an experienced nuclear weapons state to make into more than one nuclear device with an explosive yield of many kilotons. But how quickly Iraq could do so remains a matter of conjecture. The following summarizes what we have learned in recent months.

More safeguarded highly enriched uranium, but some less usable. Until the Gulf crisis came to a head late last year, U.S. officials studying Iraq's nuclear program said Iraq had 12.3 kilograms of uranium enriched to 93 percent uranium 235. This material, presumably usable in weapons, had been obtained from France for use in the Osirak research reactor, which Israel bombed in 1981.

In addition, Iraq possessed a small but publicly unknown quantity of material enriched to 80 percent uranium 235, supplied by the Soviet Union and under IAEA safeguards. Before the Gulf War, several U.S. and IAEA officials said they believed that this material totaled about 10 kilograms, and that much of it had been irradiated (burned as fuel) in a small, Soviet-supplied research reactor at Tuwaitha. This would present a problem for Iraq: the greater the irradiation of the fuel, the less uranium 235 it would contain, and the more difficult it would be to chemically extract the remaining highly enriched uranium. Of course, it would in any case take more 80 percent-enriched material than 93 percent material to make a bomb.

Documents that Baghdad submitted to the United Nations in late April confirmed that Iraq had 12.3 kilograms of 93 percent enriched fuel. Less than half a kilogram of it, however, was "fresh"; the rest had been slightly irradiated, making it more difficult for Iraq to use in a weapon. Iraq was believed capable of extracting and purifying uranium from fresh reactor fuel, but until recently, not from "spent" (fully irradiated) fuel. During a May inspection at Tuwaitha, IAEA officials were surprised to find that Iraq had separated two grams of plutonium from irradiated materials. This indicates that Iraq may have been able to retrieve usable bomb material from irradiated fuel.

But the documents also stated that Iraq had over three times as much 80 percent enriched fuel as our earlier sources indicated--33 kilograms- -and 13.7 kilograms of this fuel was fresh. The rest had been irradiated: 4.4 kilograms remained in the reactor core, partially irradiated; 14.9 kilograms was "spent fuel," that is, fully irradiated.

Iraq also indicated that it possessed 4.5 kilograms of 36 percent enriched fuel-one kilogram spent, the rest fresh. This is also classified as highly enriched, but it is much less useful for a weapon. All the material that Iraq declared was located at Tuwaitha. U.N. inspectors confirmed that the material was there, although some of it, including that in the Soviet-supplied reactor, was buried under rubble.

In mid-July the highly enriched uranium was expected to be removed from Iraq shortly. Britain and France have agreed to take it.

In all, only about 14 kilograms of the 80 and 93 percent enriched uranium were unirradiated and could quickly have been made into a weapon, if Iraq was ready to do that. In addition, the nearly 12 kilograms of slightly irradiated 93 percent material and the partially irradiated 4.4 kilograms in the reactor might also have been recoverable.

Ignoring the fully irradiated material, Iraq had 25-30 kilograms of highly enriched uranium, putting the country somewhat closer to a nuclear weapon than it would have been with only 15-20 kilograms. But U.S. laboratory experts who during the crisis puzzled over whether Iraq would make a grab for the material and shape it into bomb components do not believe the additional quantity would have made much difference. According to one, "The extra material would allow Iraq more latitude in material economies during manufacture, but would provide no breakthroughs which would dramatically reduce reflector requirements or provide greater confidence about the probability of success."

More ways to make a weapon

In our earlier article we concluded that with such a small quantity of fissile material, only an implosion (Nagasaki-type) device was possible. But Carson Mark, former head of the Theoretical Division at the Los Alamos National Laboratory in New Mexico, has expanded on the theoretical possibilities of making nuclear explosive devices with small amounts of highly enriched uranium.

In a paper written for the Nuclear Control Institute, Mark theorized that with the 12.3 kilograms of 93 percent enriched uranium, Iraq might have been able to make a device weighing about a ton with a yield of about 10 kilotons-provided it made "commendably effective use of the implosion method." The device would also require a very thick beryllium metal reflector around the core; if another type of reflector were used, the device would weigh "several times more." Such devices might be too bulky to be deliverable by Iraqi attack aircraft.

In addition, if the 93 percent material were blended with about 10 kilograms of the 80 percent enriched uranium, Mark believed that it might just be possible to make a gun-type (Hiroshima bomb) device with a yield of one or two kilotons-also if a thick beryllium reflector were used. Mark said a gun-type device is easier to build than an implosion device but has many demanding mechanical requirements.

Mark said that these calculations did not take into account numerous problems Iraq would have to solve in order to build a successful device. He estimated that "for a new project to have a device in hand a fairly large and competent staff, with diverse experience and capabilities, with all necessary bureaucratic support (but free of bureaucratic supervision) would have to work intensively for at least a year."

Iraq probably lacks beryllium. In designing a weapon with a small amount of fissile material, beryllium is essential, as Mark has pointed out, to reduce the weight and size of the device. But the Israeli Defense Forces concluded, in an assessment of Iraq's nuclear weapons capability compiled in February, that Iraq probably has no beryllium. The assessment also estimated that Iraq would need up to two years to produce a primitive weapon that would poison large areas with radioactive fallout, without a full-fledged nuclear blast, and five years to produce a 5-kiloton device of the type that destroyed Hiroshima.

Little warhead proficiency

According to W. Seth Carus, an expert at the Washington Institute for Near East Policy, assertions that Iraq could put a nuclear warhead on a 1960s-vintage ballistic missile any time soon are "far-fetched." Information available about Iraq's chemical warheads suggests that they are "fairly crude" and fused to explode on impact, he said in an interview. Iraq may have desired to make a nuclear warhead for a ballistic missile, "but that is a long-term concern-five years away or more- not an immediate one," Carus concluded.

The tradeoff between weight and range is great in Iraq's modified Scud-B missiles. A nuclear weapon on such a missile, launched at an Israeli target, Carus said, "would have to weigh less than 200 kilograms." Mark's designs would weigh over a ton.

The components of a nuclear warhead require great protection from forces of gravity and other stresses during flight. The fact that some of the Scuds used in the Gulf War broke up in flight suggests that Iraq "could not build a rugged device which could withstand normal stresses required, let alone handle the requirements of nuclear warheads," Carus said.

Experts confirm Iraq lacks metallurgical skills. It takes more nuclear material to make a bomb than the final components contain, because the components must be machined into precise form. The smoother and more precise the shape must be, the more scrap is created in trimming and smoothing. The scrap can be recovered and used in other components if more than one device is produced, but precision machining, with minimal loss, is especially important if only one or two devices are being made from a small amount of material.

With extensive experience, scrap can be kept to 10 percent for a solid, simple shape. But U.S. and European officials have surmised that Iraq does not have the expertise in metallurgy and metal machining to keep losses so low. They point out that lack of expertise in precision diemaking held up Iraqs effort to manufacture centrifuges. They also note that when Iraq bought a quantity of maraging steel (possibly for missiles) from a German firm in 1990, German experts had to perform the purity tests because Iraqis could not have done the tests reliably.

Neutron initiators a major problem. Iraq would probably need steady access to a supply of polonium 210, which is used with a small amount of beryllium as a neutron initiator for either an implosion or a gun system. The amount of beryllium is small and easily obtained, but that is not the case for polonium 210. The isotope has a radioactive half-life of only 138 days and is extremely hazardous to handle. It can be obtained by extraction from radium or from large quantities of uranium, or by irradiating bismuth in a reactor. Some external neutron generators are commercially available, but they might not be usable in an implosion system, which requires microsecond timing to initiate the chain reaction.

Still no uranium mine

U.N. officials said they asked the United States to reevaluate the possibility that uranium was being mined in the Gara Mountains in northern Iraq, near the Turkish border, as media accounts--notably CBS's Sixty Minutes--suggested in late 1990. Diplomatic sources say that U.S. intelligence investigated the suspected site but found no evidence of a uranium mine there.


A final assessment of Iraq's nuclear program must await analysis of all information obtained in the field by U.N. inspectors. We remain convinced that Iraq would have needed about a year to build a crude explosive device, but we now believe that Iraq might have developed a usable nuclear arsenal in as little as two or three years.

Since the end of the war, U.S. officials said, no new evidence has surfaced about Iraq's ability to make a nuclear bomb. Because Iraq now appears to have needed a few years to produce significant quantities of highly enriched uranium, Iraq might have had sufficient time to design a nuclear bomb and develop confidence in the design.

The revelation that Iraq had spent as much as $8 billion on its calutron program implies that Iraq sought to develop a large and renewable weapons material stockpile. It might also imply that Iraq did not intend to divert a small quantity of safeguarded nuclear material, as many observers had feared before the war. If Iraq had tried to make one or two weapons in a hurry, the prospect of success would have been far from certain and might in any ease have provoked nuclear retaliation.

While the calutron revelations are alarming, a nuclear weapons program requires more than equipment to produce fissile materials. Iraq lacked the hands-on experience required to nudge its fledgling gas centrifuge program out of the laboratory and into the large-scale production phase. No information to date suggests that Iraq would have escaped serious difficulties as it moved from a calutron pilot stage to large-scale production of highly enriched uranium.

The revelations have raised hard questions about the quality of reconnaissance information on Iraq's nuclear effort. But the heat fingerprints left by a large calutron production plant would become visible only after the facility was producing enriched uranium. One U.S. intelligence official said, "Either we really screwed up and missed it, or they just didn't get that far."

U.N. and U.S. State Department officials have expressed exasperation with the inaccurate and highly speculative assertions being circulated by some members of the U.S. administration, in an apparent effort to intimidate Iraq and oust Saddam Hussein. U.N. officials have accused the Pentagon of using worst-case scenarios to discredit the multilateral inspection effort in Iraq.

While the U.S. leaks drew ire at the IAEA, by mid-July, ironically, the Pentagon seemed to be coming around to the view that bombing Iraq' s nuclear facilities would not eliminate Iraq's nuclear capabilities. One Pentagon official said, "We can bomb all we want, but we'll never get all Iraq' s material and equipment by bombing. We can use bombing as a technique to punish Saddam or scare him. But when the dust has settled, you still could have some material left plus the nuclear experts."

Tracking down and eliminating Iraq's nuclear weapons capabilities under the terms of Resolution 687, and a continued embargo to halt imports of relevant technologies and equipment, will be the most effective way to prevent Iraq's nuclear program from resurfacing.



As pressure mounted to "complete the job" done by Operation Desert Storm and topple Saddam Hussein, U.S. officials once again hyped Iraq's nuclear threat through leaks to the media-and the media eagerly cooperated, just as it had (lone when the United States was preparing to go to war. Administration officials, quoted in one of the first calutron stories (Washington Times, June 11), said that Saddam Hussein had managed to secretly produce and hide 40 kilograms of highly enriched uranium and planned to build an atomic bomb this year. The 40-kilogram estimate has not survived the scrutiny of U.S. officials; however, it resurfaced in media accounts throughout June and July.

In July, just before the Pentagon announced it had targeted 20 command-and-control sites in Iraq for further bombing strikes, Washington officials leaked information to reporters from the New York Times and the Washington Post. Both papers then published accounts that Iraq might already have produced a bomb's worth of highly enriched uranium. The reports did not say that the estimate was a worst-case scenario, or that there was no evidence for the scenario.

As President Bush was talking up the military option with leaders in London and Paris, Reuters News Agency reported that a secret U.N. study indicated that "Saddam Hussein could produce 2040 nuclear weapons."

A State Department official said that the "grandiose" press reports, which appeared when the U.S. administration was renewing pressure on Saddam Hussein to cooperate with the United Nations, exaggerated Iraq's nuclear capabilities.


A calutron consists essentially of an intense source of uranium ions, a way to accelerate the ions to high energy within a vacuum system, and a way to collect the uranium 235 and uranium 238 ions after they have moved in separate areas between the poles of a very large electromagnet. The components at the heart of the system are ion sources, collectors, and high-voltage, regulated direct-current power supplies.

An ion source unit is basically a box, one foot by two feet by ten inches, with a slit in it and a hot filament inside. Electrons "boiled" off the filament ionize uranium vapor that is admitted into the ionization chamber. Accelerating electrodes extract the ionized uranium vapor through the slit and create a beam by increasing the particles' energy to about 30-35 thousand electron-volts. Production calutrons at Oak Ridge in the mid 1940s had one to four ion sources in each machine. Experts say Iraq' s machines could have had two to six ion sources; however, it is difficult to use more than four.

The efficiency of a calutron is limited by the difficulty of ionizing the uranium. Most of the uranium is deposited on the inside of the ion source and in the vacuum chamber, not in the collectors; it must be recovered later by scrubbing and chemical processing.

There are other problems. The uranium tetrachloride used in calutrons is not as corrosive as the uranium hexafluoride used in most other enrichment technologies. But during ionization, chlorine is released and it reacts with materials in the ion source. And during the Manhattan Project, insulators on the accelerating electrode within the vacuum chamber often cracked from heat. The affected calutron would have to be shut down and the broken insulator replaced.

In its July 7 report, Iraq said it could produce 70 kilograms a day of uranium tetrachloride, enough to supply several hundred ion sources.

The ion sources and accelerating system require high-voltage, regulated direct-current power supplies in order to produce uranium beam currents of up to a few hundred milliamperes with a precisely defined energy. (Precision is necessary to keep the beams on target.) The power sources must also be protected with special circuitry against frequent sparking in the ion source. The power sources Iraq obtained from Hipotronics [page 20] could have been modified to accelerate several ion beams in a single calutron.

The collectors for the uranium vapor beams are usually located 180 degrees from the ion source. They are typically made out of graphite, with precisely machined slits to admit the beams. Graphite is relatively easy to machine, and because it can be burned it simplifies the chemical recovery of uranium. The collectors are essentially disposable.

One of the more delicate tasks in operating a calutron is focusing and maintaining stable beams inside the vacuum chamber. Because the beam particles have the same electric charge, electrostatic repulsion causes the beam to spread. The rate of repulsion can be reduced by having positive beam particles collide with gas molecules in the vacuum chamber, creating electrons that tend to neutralize the repulsion. Reducing vacuum in the beam region will increase neutralization, although it will also increase loss of uranium in the beam. Once good beam conditions are established and the beams, are going into the collector, only occasional adjustments are necessary. In a calutron with several ion sources, however, the failure of one beam can cause all the beams to fail. Other techniques are available to improve the focus and stability of the beams.

Other components present fewer technical challenges: The large vacuum chamber is situated between the pole faces of the electromagnet. "Forepumps" are used to begin pressure reduction; vacuum is maintained primarily by one or two high-capacity diffusion pumps with pipe-throat diameters of 15-20 inches. Iraq attempted to buy 27 such pumps from CVC Products., Inc., in Rochester, New York, in 1989, but the shipment was seized by U.S. Customs.

Special disposable stainless steel, water-cooled liners are often used in the vacuum chamber to simplify recovery of the large amounts of uranium that end up on the chamber surfaces.

A calutron electromagnet has two circular poles, separated by a gap 30-60 centimeters wide in which the vacuum chamber is inserted. The magnet is typically about one to two meters in diameter, weighs about 10- 20 tons, and contains about a quarter-mile of thick copper wire. These extremely powerful magnets use one-third to one-half of the energy consumed by calutrons, and require cooling.

The power supply for the magnets requires a direct-current capacity of about 1,000 amps at 300-800 volts-similar to that used to power elevators. But the ones for calutron magnets must also be regulated precisely to produce a stable magnetic field.

Calutrons are combined into production units called racetracks. The beta calutrons at Oak Ridge were positioned in two rectangular tracks, each containing 36 calutrons in two 30 meter-long parallel arrays and joined across their ends by 10-meter iron yokes to make a closed magnetic circuit.

The associated chemical processing area is usually one of the largest parts of the plant. In this area the collectors are burned and the uranium is recovered from the ashes. In addition, the waste uranium must be recovered from the other calutron components, by scrubbing with nitric acid, soaking in acid baths, or burning or dissolving away disposable components.

The power supplies, magnets, and other components require extensive cooling with oil or purified water. Iraq built plants to purify and chill water at Tuwaitha and Tarmiya.

Sources: L.O. Love, "Electromagnetic Separation of Isotopes at Oak Ridge," Science (Oct. 26, 1973), pp. 343-52; H. London, Separation of Isotopes (London: George Newnes Ltd., 1961); U.S. Department of Energy, Nuclear Proliferation and Civilian Nuclear Power; Vol. II.: Proliferation Resistance(1980);interviews with experts.


Iraq's July 7 report to the United Nations revealed that Iraq had been pursuing three paths to enriching uranium: calutrons, chemical processes, and centrifuges. Although the calutron effort was the predominant one, the report shed a little light on the other programs:

Chemical enrichment. Iraq began work in mid-1989 on two methods of chemical enrichment, of which the report gave few details. An unofficial translation says the two methods are "liquefaction and ion [unintelligible]." This may refer to solvent extraction, a method the French are developing commercially, and an ion-exchange method the Japanese are developing. Iraq asserts that it had a "good comprehension of the chemistry of the processes" but had not completed the "laboratory technical systems" before they were destroyed by bombs.

Chemical enrichment depends on a slight tendency of uranium 235 and uranium 238 to concentrate in different molecules when uranium compounds are continuously brought into contact. The French method involves combining two immiscible uraniumbearing liquids in a column-an effect similar to shaking a bottle of oil and water. The Japanese process involves an aqueous liquid and a finely powdered resin through which the liquid slowly filters. Both processes depend on catalysts to speed up the chemical exchange.

One enrichment expert believes that Iraq could not have got very far in these technologies. Although Iraqi scientists might well have understood the principles, it would have been difficult to develop the catalysts and the processes to recycle the uranium compounds back into the separation columns.

Gas centrifuges. The report confirmed what was widely known before the Gulf War-that Iraq was working on gas centrifuges to enrich uranium. The most important statement in the report was Iraqs admission that it had a model centrifuge in which a small amount of separation had been achieved. The centrifuge had been damaged by the bombing. A U.S. official familiar with intelligence information said this was the first indication he had seen that Iraq had introduced uranium hexafluoride (the gaseous feed compound) into a centrifuge. Iraq said in the report that it had produced about half a kilogram of uranium hexafluoride.

The statement implies, however, that Iraq was working only on an archaic trouble-plagued centrifuge design developed before centrifuge technology was classified in the 1960s. This contradicts information we published in our March article, and which we still believe to be true: that Iraq obtained the design of an early Urenco centrifuge, which is a considerably more capable machine than the Beams-type machine referred to in the report. Iraq attempted to acquire centrifuge equipment matching Urenco design specifications from the Swiss firms Scheublin, SA, and Schmiedemeccanica, SA. According to a German enrichment expert who visited Iraq, this program was in an early development stage.


Reprinted by permission of The Bulletin of the Atomic Scientists, copyright 2001 by the Educational Foundation for Nuclear Science, 6042 South Kimbark, Chicago, Illinois 60637, USA. A one year subscription is $28.








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