Aluminum Tubing Is an Indicator of an Iraqi Gas Centrifuge Program: But Is the Tubing Specifically for Centrifuges?

Updated October 9, 2002

The September 12, 2002 White House White Paper, A Decade of Deception and Defiance states:

"Iraq has stepped up its quest for nuclear weapons and has embarked on a worldwide hunt for materials to make an atomic bomb. In the last 14 months, Iraq has sought to buy thousands of specially designed aluminum tubes which officials believe were intended as components of centrifuges to enrich uranium."

The Bush administration has released few details supporting its statement about aluminum tubing. However, there are a growing number of leaks to the media and additional information that collectively shed light on this statement.

U.S. officials have said that a number of secret shipments intended for Iraq have been stopped or intercepted. These officials have refused to name the countries or companies involved. Nonetheless, the Associated Press reported on September 13, 2002 that one of these shipments originated in China and got as far as Jordan before being intercepted.

Upon analysis of the procurement information, technical analysts at the CIA became convinced that the items were for use in an Iraqi gas centrifuge program, a uranium enrichment technology that Iraq had intensively developed between 1987 and early 1991. Because the parts had certain specifications and were ordered in large numbers, the analysts concluded that the parts were intended for the serial production of thousands of centrifuges. Because each centrifuge enriches a relatively small amount of uranium, several thousand centrifuges must be connected by pipes into "cascades" in order to produce annually enough highly enriched uranium for a nuclear weapon.

Other U.S. intelligence and nuclear analysts, however, have challenged the conclusion that the tubes could only be intended for a gas centrifuge program. These analysts have concluded that the tubes are "dual-use" items that could have been intended for non-nuclear uses. Several government experts said that the tubes could be for conventional weapons programs, including artillery or anti-tank rockets. Thus, the dispute is whether enough evidence exists to state that the tubes were definitely ordered for the gas centrifuge program.

First Public Revelations

The first public report of the tubing was in The New York Times on September 8, 2002. This report quoted unnamed administration officials stating that the tubes were for centrifuge parts and were intended as "casings for rotors." The link to centrifuges, according to this report, was based on the number, specification, and dimensions of the tubes the Iraqis sought to purchase.

The Washington Times actually first reported this story publicly. But in its July report it erroneously listed the material as stainless steel instead of aluminum. Because stainless steel is not a material critical to gas centrifuges, the story was viewed as inaccurate and did not attract much interest.

The leak to the New York Times appeared to have been timed, or was at least used, by the Bush Administration to help build its case that Iraq was close to getting nuclear weapons. Senior administration officials mentioned the tubes many times as they made their rounds on the Sunday television talk shows the same day the story was published. Condoleezza Rice, the National Security Advisor, said on CNN Late Edition on September 8, 2002 that the aluminum tubes "are only really suited for nuclear weapons programs, centrifuge programs." The Vice President reinforced this point on NBC's Meet the Press, stating that Saddam Hussein "now is trying, through his illicit procurement network, to acquire the equipment he needs to be able to enrich uranium-specifically aluminum tubes."

Soon afterward, voices of dissent started to be heard. A September 13, 2002 New York Times article stated that although the CIA position appears to be the dominant view, some experts in the Department of Energy and the State Department questioned this conclusion. According to the New York Times report, the administration has shown great sensitivity about suggestions that intelligence experts differ over Iraq's intentions, because Iraq's pursuit of weapons of mass destruction (WMD) is the centerpiece of the argument for planning a military attack to overthrow Saddam Hussein's regime.

An intelligence official told the media that the statement in the White Paper quoted above was toned down. The CIA asked the White House to do so to reflect dissenting opinions and also to give the United States a "little wiggle room." Reflecting this uncertainty, another intelligence official added that the aluminum tubing was "not a smoking gun."

In fact, the intelligence community is deeply divided about the purpose of the tubing, with a significant number of experts knowledgeable about gas centrifuges dissenting from the CIA view. It appears that the New York Times stories represented only one side of this debate.

ISIS has learned that U.S. nuclear experts who dissent from the Administration's position are expected to remain silent. The President has said what he has said, end of story, one knowledgeable expert said.


High strength aluminum is a nuclear dual-use item, which means it has both nuclear and non-nuclear uses. Under Security Council resolutions, Iraq is banned from possessing aluminum tubing above a certain strength, unless these items are imported through the UN, used for civilian or non-banned purposes, and subject to monitoring by inspectors.

Iraq has conducted illicit procurement for decades to bolster its conventional armaments and WMD programs. Its efforts before the Persian Gulf were legendary and demonstrated its extraordinary ability to procure items secretly for its conventional military, ballistic missile, and WMD programs. Looking back, the sensitive dual-use items detected by Western authorities before the Gulf War represented only the "tip of the iceberg." After the imposition of the UN embargo in August 1990, Iraq continued to smuggle items.

Given persistent Iraqi attempts to smuggle sensitive items, Western intelligence agencies closely monitor Iraq and its agents to determine what Iraq is attempting to procure and significant efforts are made to stop illicit procurements. If a smuggling effort is detected, government experts evaluate whether the shipment or order may involve items for any proscribed activity.

Aluminum alloy has many military and civilian uses, including aircraft, bike frames, ballistic missiles, and gas centrifuges. However, procurement of high-strength aluminum is considered an indicator of a secret gas centrifuge program (see table, will open in a new window). Detection of an indicator normally increases suspicion that a secret activity is being pursued, but it does not prove the existence of a secret centrifuge program without additional evidence to establish a direct link.

Determining an exact use of aluminum tubing is difficult without the cooperation of Iraq or the presence of inspectors in Iraq. Without such capabilities, analysts must evaluate the item itself, looking at its specifications including its type, dimensions, and any modifications made to the tube. The primary goal of analysis in this case is to determine if the part was specifically manufactured for gas centrifuges, or the technical specifications of the tubes strongly imply their use in gas centrifuges. The latter case could be bolstered by looking at other items Iraq tried to import and by evaluating the significance of the overall procurement effort.

In addition, insider or intelligence information could be critical. For example, a company official could have been told, deliberately or inadvertently, the true end-use of the part and subsequently informed authorities.

The CIA Case

The administration claims that these intercepted shipments are specific to centrifuges. The public evidence for this case is fragmentary and the government has released little officially. Instead, unnamed officials have released a series of difficult to understand statements to the media, including:

Nothing in these statements provides technical evidence that the tubes were intended for centrifuges.

Two Shipments

The media has discussed two distinct shipments of tens of thousands of aluminum tubes to Iraq-referred to here as an earlier one and a more recent one. Intelligence sources have told the media that multiple shipments were attempted, but no specific number has been revealed. Thus, whether more than two shipments were intercepted is unknown.

Intelligence officials have stated that they are not aware of any aluminum that got through to Iraq. But these officials make clear that they believe other shipments likely exist, and some shipments may have gotten through to Iraq.

Earlier Shipment A shipment was stopped over a year ago and maybe the one that marked the start of the 14-month period the administration mentions. The purpose of this shipment of aluminum tubing was debated extensively in the intelligence community.

A CIA assessment of this shipment linked the tubing to centrifuge components. However, others in the intelligence community, particularly in the Department of Energy or its national laboratories, disagreed and said that other non-nuclear uses were possible.

Based on available information, this order was for tens of thousands of tubes made from 7000-series aluminum alloy and with a tempering or heat treatment specification of T6. This type of aluminum is alloyed with zinc and is very strong. The heat treatment in this case makes for a hard metal. The tubing was apparently "perfectly fitted" on each end, implying that the tubes were intended to be that length. The diameter of each tube was reportedly about 3 inches (about 75 millimeters) and they were about one meter long. The wall thickness was a few millimeters.

Outer Casing The diameter of these tubes is significantly less than the outer casing used in Iraq's centrifuges that were being constructed in the late 1980s, and their wall thickness appears too small for an outer casing. Outer casings are rather non-sensitive centrifuge components that are thick-walled tubes designed to contain a failing rotor and preserve the vacuum of the machine.1 The failure of the vacuum in a single centrifuge casing can cause the destruction of the entire cascade.

In the late 1980s, Iraq ordered thousands of 6000-series aluminum tubes for the outer casing of its centrifuges. These tubes had diameters sufficient to hold rotors with a diameter of 145 millimeters (see figure 1, will open in a new window).

Iraq's outer casings were welded. Aluminum of the 6000-series is the best for welding, while 7000-series aluminum is not recommended for welding.

Centrifuge Rotor A much more likely candidate for a centrifuge component is the rotor, a thin-walled tube that spins at high speeds, causing the uranium to enrich in the isotope uranium 235. A centrifuge rotor is a highly sensitive object that requires specialized high strength material.

There were many old centrifuges that used aluminum rotors, and Iraq pursued at least one of them. When the Iraqi centrifuge program started, it focused on the archaic 1941 "Beams-type" centrifuge design, named after its U.S. originator, Jessie Beams. The Iraqi design used a four-inch diameter duralumin pipe, an old aluminum alloy that is equivalent to 2000-series aluminum. The thickness of the Iraqi rotor is unknown, but the Beams-type rotors built in the United States had a wall thickness of less than one millimeter and the Iraqis copied this design.2 2000-series aluminum is not as strong as 7000-series aluminum, but it is stronger than 6000-series aluminum. Iraq could possibly replace the 2000-series aluminum in the Beams-design with 7000-series aluminum. The outer casing of Iraq's Beams-type centrifuge consisted of a steel pipe with welded upper and lower flanges.

Iraq could also use aluminum in a more modern centrifuge design that it was developing in the late 1980s called the "Zippe-type" centrifuge, named after one of its main developers, Gernot Zippe. The first centrifuges of this type were developed in the 1950s and 1960s, and they also used duralumin rotors. However, Iraq had invested heavily in making maraging steel and carbon fiber rotors for its Zippe-type centrifuges (see figure 2, will open in a new window). Both materials are more advanced than aluminum and allow the rotor to spin considerably faster. However, Iraq encountered difficulties in building them, despite extensive assistance from German experts.

Despite the disadvantages, Iraq could have decided to pursue aluminum rotors because it could get the aluminum tubing easier than those other materials. Unlike outer casings, aluminum rotor assemblies do not require welding, therefore the 7000-series aluminum could be used for rotors. Iraq may also feel more confident making aluminum rotors than maraging steel or carbon fiber rotors. Iraq's extensive knowledge of early German and Urenco centrifuge designs enable it to modify its established Zippe-type designs to use aluminum rotors. Iraq's use of this design is more likely than a Beams-type design, given its knowledge and experience.

The dimensions of Zippe-type centrifuges made with aluminum rotors are publicly available. The rotors typically have diameters between 50 and 100 millimeters and a length of about 50 centimeters.3 Their wall thickness was less than one millimeter. Thus, the dimensions of the aluminum tubes Iraq sought are consistent with centrifuge use, assuming that the tubes would be cut and the walls significantly thinned. Zippe-type centrifuges that used aluminum rotors in the late-1950s and the 1960s used a T6 hardening. As a result, cutting would not present any obstacles. However, whether two rotors could be made from each tube is unknown. In addition, the special hardening would permit the tubing wall to be shaved down to the required thickness for a centrifuge rotor. A good tool, however, would be required to thin the tube thickness to about 0.5 millimeters.

The aluminum tubes Zippe used were not anodized or did not have any other type of coating. Uncoated aluminum works well in a centrifuge both in a rotor assembly and as cascade piping. The coating on the outer surface of the tube would be removed during the shaving operation. An anodized layer on the inside of the tube, however, can result in hampering the operation of the centrifuge, according to an expert involved in the development of Zippe-type centrifuges in the 1950s and 1960s.

Instead of a pure aluminum rotor, Iraq could also pursue a hybrid design that involves wrapping carbon-fiber or another composite material over an aluminum tube. However, in this case the aluminum tube does not need to be as strong as 7000-series aluminum.

Non-Nuclear Uses Several experts knowledgeable about this attempted procurement, including at least one expert with over a decade of direct experience with gas centrifuges, told ISIS that the purpose of the tubes could have been for non-nuclear uses. At least two of these experts concluded that the most likely intended use of the tubes was non-nuclear. They assessed that the intended use could have been for conventional rockets, such as those for multiple rocket launch systems (MRLS).

UNSCOM inspectors saw and inventoried thousands of similar high strength aluminum tubes in Iraq before they left in 1998, according to one knowledgeable expert. Iraq has a long history of ordering 7000-series aluminum tubes and plates, the expert added. Such aluminum plate was ordered in large quantities in the late 1980s for Iraq's ballistic missile program. The inspectors did not view the purpose of the tubing as being related to nuclear activities.

The CIA rejected any non-nuclear use for the aluminum tubing. The media learned that the use of the tubing was investigated by the U.S. Army National Ground Intelligence Center. It concluded that the use of this particular high strength aluminum tubing with such tight tolerances would have been "exquisite," far in advance of what is needed for a MRLS. One knowledgeable expert said he did not believe the CIA analysts presented the Army with complete information.

A knowledgeable expert said that Iraq imported 7000-series tubing for non-nuclear uses in the 1980s and 1990s. Thus, these recent attempted procurements could also have been intended for a non-nuclear use.

A technical expert who was involved for two decades in selling equipment to make rocket tubes for military purposes said he does not believe the tubes are for centrifuges. He said combustion chambers of many types of small rockets require tight specifications in their thickness and outer diameter. He also said that anodizing the outer surface of the tube would be expected in a rocket tube to create a smoother surface and prolong the shelf life of the rocket. He speculated that the tubes could have been intended for anti-tank rockets or similar items.

The debate over the purpose of the tubing left some dissenters perplexed. "Always the same answer, no matter what the objections were," one said. Inevitably, this situation led to speculation. Did the CIA have information about the tubes it was not sharing to protect important secrets? Or was the CIA arguing a view not really based in the facts? The recent statements emanating from the CIA suggest that it is not as certain about the intended purpose of this shipment as first stated.

More Recent Shipment The more recent shipment is reported to have happened about three months ago and is the one reported in the New York Times on September 8 as linked to centrifuge outer casings. Administration officials have reportedly stated that they have very specific information linking the tubes to a "rotor casing," interpreted as an outer casing.

Little information is available about the tubes in this shipment or order. If the tubes were intended for centrifuge outer casings, then they are unlikely to be 7000-series aluminum which in general is not good for welding. A wall thickness of a few millimeters, as discussed above, may not be sufficient to contain the shrapnel of a failing rotor.

Even if the CIA can make the case that the intercepted tubes are intended for outer casings, drawing implications about Iraq's gas centrifuge program from that information is difficult. Outer casings are not very critical centrifuge components. They are some of the easiest centrifuge components to fabricate and progress on outer casings says little about progress on procuring items for critical components, such as rotors, end caps, or bearings.

A relatively large diameter tube similar in size to the ones made by Iraq in the late 1980s could imply that the rotors would be made from maraging steel or carbon fiber. These materials are more difficult to obtain than high strength aluminum, and no evidence has been presented that Iraq has acquired either material. Thus, inferring information about the status of the Iraqi centrifuge program from information about the outer casing is a difficult and perhaps misleading exercise.

On the other hand, the New York Times may have been incorrect, and, in fact, the tubes were suited for rotors. If that is the case, and it appears likely, the above discussion applies here as well.

Construction of Aluminum-Rotor Centrifuges

If Iraq was building a gas centrifuge plant using machines with aluminum rotors, it would need to build a large number of machines, requiring many thousands of tubes. Aluminum rotors will spin slower and thus will have less of an ability to separate uranium than tubes made from maraging steel, carbon fiber, or other composite materials. This weakness must be overcome by building more machines.

Assuming that Iraq would build a Zippe-type aluminum rotor centrifuge, like those developed in the 1960s, the production of 10 kilograms of weapon-grade uranium per year would require the operation of about 3,500 such centrifuges.4 Each centrifuge would have an enrichment capacity of roughly 0.5 separative work units (SWUs) per year, assuming that each rotor tube has a diameter of about 75 millimeters.

Before an aluminum tube of the type in the earlier shipment could be used in a centrifuge, it would be necessary to modify it by cutting it in half and reducing its wall thickness to less than one millimeter. This task can be accomplished by cutting the tube and shaving aluminum off the wall until the required thickness is obtained. Accomplishing this task is complicated, but within Iraq's capabilities both in terms of available machine tools and expertise.

After cutting the tube to appropriate dimensions, end caps and other items would be attached resulting in a completed rotor assembly. This assembly would then be tested at low speed on an "air stand" to ensure that it performed to specifications. In the case of Iraq, many rotors would likely fail this and other quality assurance tests. Thus, Iraq would need to build far more rotor tubes and other components than it would eventually use in a centrifuge.

To develop an estimate of the time to make a centrifuge plant able to produce 10 kilograms of weapon-grade uranium a year, several assumptions must be made. The first is that about 3,500-7,000 tubes would be modified to produce 3,500 rotor tubes, where the range accounts for whether one or two rotors can be obtained from each tube and the reject rate is taken as 50 percent. This rejection rate is consistent with Iraq's expectation in the late 1980s in designing its centrifuge manufacturing facilities.

With the right equipment, skilled technicians can make a rotor in two hours, according to an expert involved in developing both the early Russian and German gas centrifuges that used aluminum rotors. Assuming another two hours to assemble and test the rotor assembly, one machine operating 24 hours a day, seven days a week could make 2,200 rotors a year. Assuming about half are rejects, then annual production is about 1,000 centrifuges of required specifications per year at a clandestine facility.

Thus, in this scenario Iraq is estimated to need about 3.5 years to make a centrifuge facility with enough centrifuges to make 10 kilograms of weapon-grade uranium per year. Given about 15-20 kilograms of weapon-grade uranium per weapon, Iraq could produce enough material for a bomb every 1.5-2 years.

This estimate may be too short because it fails to account for the requirements that Iraq must also produce other centrifuge parts in large number, master the assembly of whole centrifuges and cascades, develop a sufficient stock of uranium hexafluoride, and go through the start-up phase of the centrifuge plant. Accidents and other setbacks may further increase the time to produce the first bomb's worth of weapon-grade uranium. Disrupted procurement efforts can significantly delay progress on building a plant.

If Iraq used a supply of low enriched uranium that it acquired illicitly or diverted from a safeguarded stock in Iraq at the Tuwaitha nuclear site, it would need far fewer centrifuges or it could make a given amount of weapon-grade uranium significantly faster.


Based on the available information, the intercepted aluminum tubing could have been intended for use in a centrifuge. It is far harder to confirm the Administration's view that the tubes were specifically intended for use in a centrifuge. The earlier shipment does not appear to be specific to centrifuges, as initially claimed by the Administration. The more recent shipment is hard to assess with the available information, but even the detection of efforts to make an outer casing of a centrifuge provides limited insight into Iraq's gas centrifuge efforts.

By themselves, these attempted procurements are not evidence that Iraq is in possession of or close to possessing nuclear weapons. They also do not provide evidence that Iraq has an operating centrifuge plant or when such a plant could be operational.

These attempted procurements do show that Iraq may have accelerated its efforts to obtain banned items. Despite the lack of evidence linking the tubes to centrifuges, these procurements have increased suspicions about Iraq's nuclear efforts. As a result, greater scrutiny is needed of all Iraqi procurement efforts. Iraq would need to acquire many items to build a centrifuge plant. A more comprehensive evaluation may shed a clearer light on any Iraqi effort to build gas centrifuges.

Iraq's attempted procurements of aluminum tubing point out the need for intrusive UN Security Council-mandated inspections in Iraq. If inspections would resume in Iraq, they could carefully follow up these attempted procurements. Iraq would have to explain these attempted procurements, either admitting they were intended for centrifuges or provide a compelling case that the end use was non-nuclear.

One hopes that the CIA has special intelligence information supporting its case about the intended use of these tubes. This possibility, however, appears increasingly remote. The British government said recently in its assessment of Iraq's WMD programs that "there is no definitive intelligence evidence that [the specialized aluminum] is destined for a nuclear programme."

The Administration needs to make more information available. The dimensions, specifications, and any other distinctive characteristics of the tubing should be released. Other information tying these tubes to centrifuges should be provided, while adequately protecting intelligence sources and methods. Otherwise, the Administration should accept that many states and members of the public will question both its conclusions and intentions.

1 Outer casings are also called housings or recipients.
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2 The Iraqis used a subcritical Beams design, which would mean that the length of the rotor was about 50 centimeters. The separative capacity of each machine was less than 0.5 SWU/yr.
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3 Longer rotors could be built, for so called "supercritical" centrifuges. The rotors would need a specialized flexible joint called a bellows that would be inserted between rotor segments that are about 50 centimeters each.
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4 If Iraq instead decided to build a Beams-type centrifuge in large numbers, it would need to build more centrifuges than if it pursued Zippe-type aluminum rotor centrifuges. It would also need to overcome many technical problems, perhaps more problems than if it decided to build a Zippe-type machine.
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