A Little More On the Aluminum Tubes

By Simon Henderson, adjunct scholar The Washington Institute for Near East Policy

As the advance towards war against Iraq continues, the Bush administration has started lobbing missiles at hardline liberals ever unconvinced about the threat Saddam Hussein poses to his region and the world. The administration's game presumably is to make these diehards change their minds and to win over skeptical members of the public.

One of the latest missiles involves aluminum tubes. But the story here is complicated, and thus might confuse rather than clarify the danger of Saddam.

On September 8, the New York Times reported: "In the last 14 months, Iraq has sought to buy thousands of specially designed aluminum tubes which American officials believed were intended as components to enrich uranium. American officials said several efforts to arrange the shipment of aluminum tubes were blocked or intercepted but declined to say, citing the sensitivity of the intelligence, where they came from or how they were stopped."

Having leaked the story, the administration ran with it. September 8 was Sunday, and Vice President Cheney, speaking on NBC's "Meet the Press," referred to the aluminum tubes. "What we have seen recently is that [Saddam Hussein] is trying through his illicit procurement network to acquire the equipment he needs to be able to enrich uranium."

A September 10 analysis by the BBC's defense correspondent, Paul Adams, mentioned Cheney's comments but noted pointedly, "Experts say the shipment does not necessarily prove anything." The BBC quoted John Wolfstahl, deputy director of the Non-Proliferation Project at the Carnegie Endowment, as saying: "It's disturbing but by no means a smoking gun." A further quotation came from David Albright, president of the Institute for Science and International Security in Washington: "It's a weak indicator. A lot of people disagree with Cheney."

One hopes these experts did not do the public a disservice. After all, the New York Times story also said: "The diameter, thickness and other technical specifications of the aluminum tubes had persuaded American intelligence experts that they were meant for Iraq's nuclear program." It seems a strong indicator.

For the perplexed, a short science lesson is necessary. An atomic bomb can be made from either plutonium, obtained from reprocessed fuel rods in a nuclear reactor, or from highly enriched uranium. Normal uranium is no good, as it contains only 0.7 percent of the fissile isotope U-235. Centrifuges are one way of extracting the U-235 and bringing it up to the 90 percent strength needed for a bomb.

Building such a centrifuge is an engineering challenge. It works on the same principle as fairground rides in which the young and foolhardy are spun around and pinned against the wall by the centrifugal force. In an enrichment plant, a gaseous form of uranium is introduced into a centrifuge spinning about 1,000 times per second. Some separation is achieved from the more dominant U-238 isotope before the gas is passed to another centrifuge to repeat the process. After the uranium passes through a thousand or more centrifuges, known as a cascade, a dribble of highly enriched uranium emerges. Left operating for about a year, a cascade can produce the 25 kilograms or so required for a nuclear bomb.

Aluminum centrifuges are old-tech, even by Iraqi standards. When United Nations inspectors went in after the Gulf War they discovered that Iraq had been trying to build centrifuges made from a much stronger specialty steel, known as maraging steel, and even carbon fiber, which is lighter than steel and can be even stronger (explaining why many yachts now have carbon fiber masts). Because these materials are so strong, centrifuges made from them can spin faster, making separation of the U-235 isotope many times more efficient.

The weapons inspectors destroyed the centrifuges they found, along with the rest of Iraq's enrichment infrastructure, but apparently Saddam is trying again. And as in the 1980s, he seems prepared to use old technologies if they are available. Back then, using declassified U.S. data, Saddam's scientists were also building calutrons, a method considered by the Manhattan Project but rejected because enrichment by that route took too long.

By contrast, the technology for aluminum centrifuges -- developed in Europe to produce reactor fuel for power plants and submarines -- is still highly classified. Iraq obtained its plans for maraging steel centrifuges from a disaffected and greedy German scientist, since prosecuted. Pakistan, meanwhile, built its first centrifuge cascade using aluminum devices, with help from a Pakistani scientist formerly employed by the European enrichment consortium.

So the question is: Has Iraq obtained plans for aluminum centrifuges from a less-than-secure European industrial archive, or did Pakistan supply them? Back before Iraq's invasion of Kuwait, according to intelligence officials, Pakistani nuclear scientists visited Iraq, and Iraqis visited Pakistan's unsafeguarded enrichment plant at Kahuta, outside Islamabad. It seemed surprising that U.N. weapons inspectors never discovered a Pakistan connection when searching Iraqi facilities.

If the plans did come from Pakistan, were they handed over before 1990 or more recently? And what was the quid pro quo? (Pakistan is believed to have swapped its centrifuge technology with Beijing in 1983 for a design of a nuclear weapon and enough highly enriched uranium for two bombs in order to jump-start its nuclear arsenal.)

One wonders what President Musharraf of Pakistan was thinking when he sat in the United Nations in New York on September 12 listening to President Bush lay out the case for action against Iraq and the responsibility of the international community. On message, the president again mentioned aluminum tubes.

When are we going to hear more about these Iraqi procurement efforts? Perhaps in the British dossier on Iraq, expected to be released by President Bush's closest (and so far only) ally, British prime minister Tony Blair, before Parliament meets for a special Iraq debate on September 24. The officials quoted by the New York Times cited the sensitivity of intelligence as the reason for withholding details of when or where illegal cargoes were detected. That's the normal formulation for intelligence material uncovered by a foreign country. Perhaps the Iraqi buying network has been operating in Britain, or at least Europe.

There are other concerns involving Pakistan, in whose lawless border region with Afghanistan al Qaeda operatives (and maybe bin Laden) are lurking. Before September 11, 2001, two retired Pakistani nuclear scientists with detailed knowledge of the other nuclear explosive, plutonium, were in contact with bin Laden. And a few weeks ago the London Sunday Times reported that Pakistan had been trying to buy more maraging steel from a British company. Officials had ordered the company to cancel the contract, but in a farcical confusion, the shipment was still sent. (Technical note: Aluminum centrifuges are built in sections, with maraging steel joints to provide flexibility. Otherwise they shatter at high speed.)

So producing more details on aluminum tubes would help the Bush administration convince doubters, but could open a Pakistani can of worms. It could confuse the message about the unique threat posed by Saddam Hussein -- or prove it. Unfortunately, there appears to be little time to play with.

Indicators of Clandestine Production of Highly Enriched Uranium Using Gas Centrifuges

One method to produce highly enriched uranium (HEU) is by using gas centrifuges. Iraq developed its gas centrifuge technology in the late 1980s and possesses much information on making and using centrifuge components.

The clandestine procurement of uranium centrifuge enrichment technology may include the acquisition of specialized technical items, including:

Special aluminum alloys, maraging steel, or fiber composites;

Special oils, bearing technology, and magnets;

Good quality CNC multi-axis machines and inspection tools for centrifuge components;

Equipment for production of Uranium Hexaflouride (UF6), including nickel alloy components and large amounts of aluminum tubing;

Good quality sealed vacuum valves and heliarc welding equipment;

Raw fluorine, HF and preconditioning agent (i.e. CIF3).

The procurement of these items may indicate the existence of a program to manufacture centrifuge components in large quantities. With the raw materials on hand, the production of centrifuge components requires only a few workers in a clean shop.

The media has discussed two distinct shipments of aluminum tubing 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 concluded that other non-nuclear uses were possible.

Based on available information, this order was for 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 3-4 inches (about 76-100 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.

Iraqi carbon fiber rotors, destroyed by inspectors in the early 1990s.

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 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 Series 2000 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. 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 a 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. Whether two rotors could be made from each tube is unknown, however. 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 as a rotor and 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, should work fine in a centrifuge, according to an expert involved in the development of Zippe-type centrifuges in the 1950s and 1960s.

Instead of an 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.

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 would have been "exquisite," far in advance of what is needed for a MRLS. One knowledgeable expert, however, said that the Ground Intelligence Center did not receive all the information.

This 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.

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.

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 of the type he 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 about 0.5 separative work units (SWUs) per year, assuming that each rotor tube has a diameter of about 75-100 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.

REMARKS TO THE UNITED NATIONS SECURITY COUNCIL SECRETARY OF STATE COLIN L. POWELL Orders were issued to Iraq's security organizations, as well as to Saddam Hussein's own office, to hide all correspondence with the Organization of Military Industrialization. This is the organization that oversees Iraq's weapons of mass destruction activities. Make sure there are no documents left which would connect you to the OMI. We know that Saddam's son, Kusay, ordered the removal of all prohibited weapons from Saddam's numerous palace complexes. We know that Iraqi government officials, members of the ruling Baath Party and scientists have hidden prohibited items in their homes. Other key files from military and scientific establishments have been placed in cars that are being driven around the countryside by Iraqi intelligence agents to avoid detection. Thanks to intelligence they were provided, the inspectors recently found dramatic confirmation of these reports. When they searched the homes of an Iraqi nuclear scientist, they uncovered roughly 2,000 pages of documents. You see them here being brought out of the home and placed in UN hands. Some of the material is classified and related to Iraq's nuclear program.

Tell me, answer me: Are the inspectors to search the house of every government official, every Baath Party member and every scientist in the country to find the truth, to get the information they need, to satisfy the demands of our Council? Our sources tell us that in some cases the hard drives of computers at Iraqi weapons facilities were replaced. Who took the hard drives? Where did they go? What is being hidden? Why? There is only one answer to the why: to deceive, to hide, to keep from the inspectors.

AND YET ElBaradei Reports: ..."There is no indication of resumed nuclear activities," he said.......ElBaradei told the council

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.