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Red Team, Part 2: The Aluminum Tubes

by FMJ Mon May 15th, 2006 at 04:05:06 AM EST

Iraq began a gas centrifuge uranium enrichment program in August, 1987 (Albright, 1997). Iraq planned to build first a working centrifuge, then a number of experimental cascades, then commission a cascade facility comprising a thousand centrifuges. Iraq's goal was to be able to produce 10kg of HEU per year by 1994 (Albright, 1997). Iraqi scientists attempted to build a Beams centrifuge, however the project was abandoned in 1989. Iraq had obtained a more advanced centrifuge design, a modified Zippe-type developed by the European enrichment conglomerate, Urenco. The Zippe/ Urenco design could use carbon fibre or maraging steel rotors. The Iraqis also acquired technical expertise in centrifuge construction from Germany. By the end of 1990, Iraq had built two working Zippe/Urenco centrifuges. Iraq would have started development of a centrifuge cascade had not its enrichment program been halted after the 1991 Gulf War (Albright, 1997).


The U.S. Intelligence Community (IC) first began to suspect Iraq may be reconstituting its gas centrifuge enrichment program in early 2001. UN weapons inspectors had left Iraq in 1998 and now an Iraqi front company was trying to buy 60,000 high-strength aluminum tubes. The front company's communications had been monitored and a contract detailing the tubes' specifications intercepted (Albright, 2003). Under Security Council resolution 687, Iraq was banned from importing high-strength aluminum tubes with outer diameters in excess of 75mm. The Iraqi aluminum tubes had an external diameter specified at 81mm.

On April 10, 2001, the CIA published its first assessment of the tubes, based on the tubes' specifications as provided by the intercepted contract. The assessment was largely the work of an analyst in CIA's Center for Weapons Intelligence, Non-Proliferation and Arms Control (WINPAC). He assessed that tubes with such specifications had "little use" other than for rotors in a gas centrifuge program (SSCI, p. 88). The WINPAC analyst has subsequently been identified in press reports as "Joe" (for example, see Gellman and Pincus, 2003). Joe, however, was not a centrifuge expert. Although he had worked on a U.S. centrifuge program, he had had no experience with the 1950s aluminum-rotor centrifuges, such as the Zippe and Beams design. Even so, Joe's theory that the tubes were intended for an Iraqi centrifuge program would eventually become the majority position of the IC in the October, 2002 National Intelligence Estimate.

Table 1 - Specifications of the Iraqi Aluminum (Al) Tubes

Length900.0mm
Outer Diameter81.0mm
(+0/-0.1)
Inner Diameter74.4mm
(+0.1/-0)
Wall Thickness3.3mm
Material7075-T6 Al
(Source: SSCI, pp. 88; 93. Duelfer, 2004, Vol. 2, p. 27)

The IC's experts on centrifuges, the DOE, also analysed the tubes' specifications. The DOE judged that the tubes were not likely to be part of a centrifuge program. The tubes' internal diameter was only "marginally large enough for practical centrifuge applications." (SSCI, p. 89). This meant that the centrifugal force inside the rotor would not be very strong. The amount of uranium the rotors could enrich in a year would be so insignificant that if Iraq wanted enough HEU for a nuclear weapon, the cascade would have to be larger than any that had ever been built.

Even if Iraq was building a small centrifuge cascade, they would require much more equipment than just high-strength tubes. Iraq would need thousands of top- and end-caps, thousands of baffles, scoops, magnetic suspension bearings, molecular pumps, and so on. None of these items had been detected, so it was unlikely that Iraq was building a cascade. Also, the manner the procurement was handled (multiple agents, multiple suppliers, price quotes, haggling) suggested to DOE that the tubes were more likely a conventional military purchase (SSCI, p. 89).

Still, the tubes were a clear contravention of UNSCR 687. Also, the IC had not yet had physical access to the tubes, just their specifications as listed on the intercepted contract. In June, the CIA seized a shipment of 2000 tubes in Jordan en route to Iraq (SSCI, p. 90; Butler, p. 131).

After the tubes' seizure, a very strange assessment was disseminated through the IC on July 2, 2001. The SSCI report redacts the name of the assessment's authoring agency but says it was based on the "inspection" of the tubes by unnamed "personnel"  (SSCI, p. 90). The personnel claimed that the tubes "are constructed from high-strength aluminum (7075-T6) and are manufactured to the tight tolerances necessary for gas centrifuges." Significantly, the personnel also claimed that the tubes' dimensions "match those of a publicly available gas centrifuge design from the 1950s, known as the Zippe centrifuge." The assessment concluded that the tubes' specifications "far exceed any known conventional weapons application" (SSCI, p. 90).

In mid-July, Joe the WINPAC analyst was also claiming that the tubes "matched" a Zippe centrifuge design. Joe asserted that the tubes only needed to be cut in half and they would appear very similar to Zippe's three-inch rotor design (Albright, 2003). But DOE analysts pointed out that Joe was wrong. The Iraqi tubes had walls three times thicker than any of Zippe's designs. Even if the tubes were cut in half, they would still be too heavy.

Table 2 - Specifications of the Iraqi Tubes and the Zippe 3" Rotor
Iraqi TubesZippe 3"
Length900.0mm332.0mm
Outer Diameter81.0mm76.2mm
Inner Diameter74.4mm74.2mm
Wall Thickness3.3mm1.0mm
Material7075-T6 Al2000-T6 Al
(Source: SSCI, pp. 88; 93;110)

Joe appears to have conceded the DOE's point by the end of July. The tubes' wall thickness precluded their use as Zippe 3" rotors. When Joe and a DOE analyst travelled to Vienna to address the IAEA on the tubes' significance, Joe modified his argument. He argued that the Iraqis would not only cut the tubes in half, but also machine down the walls of each tube before building them into Zippe centrifuge rotors. The IAEA was unpersuaded, however. One IAEA centrifuge expert referred to Joe's presentation as "really bad" (Albright, 2003).

It is extremely difficult to machine a high-strength aluminum tube without rendering it useless as a centrifuge rotor. A centrifuge rotor a few tenths of a millimetre lopsided is going to have significant balancing problems. So, any machining of the tubes would have to be extraordinarily precise. Also, the heat produced by machining and the way in which the tube is held can also easily distort their shape.

Although it was technically possible the Iraqis could machine 1000s of tubes to match Zippe 3" rotors it would cost the Iraqis significant time, energy and effort. As one DOE analyst noted, "you could turn your new Yugo into Cadillac with enough time and energy and effort as well." (SSCI, p. 112). By early-August, Joe had abandoned his `wall thinning' theory and instead was intent on proving the DOE wrong. Joe was searching for evidence of centrifuge rotors with walls as thick as the Iraqi tubes.

Joe's research found its way into an August 2, 2001, DIA background paper on the tubes. Joe had given a presentation that questioned the DOE's assessment that the tubes' walls were too thick and did not match Zippe rotor designs. Joe had decided to combine the dimensions of all the Zippe designs to make the tubes' inner and outer diameters appear to match. He had also decided in spite of DOE that Zippe's wall thickness could be "interpreted" as 2.8mm, not 1mm (SSCI, p. 91). And, just as the `personnel' had claimed in July, Joe argued that the tubes' wall thickness tolerance and high-strength aluminum made them suitable for use as centrifuge rotors (SSCI p. 90).

Table 3 - Specifications of Iraqi Tubes and Joe's Zippe Frankenstein
Iraqi TubesJoe's Zippe Frankenstein
Length900.0mm279.4mm - 381.0mm
Outer Diameter81.0mm74.2mm - 81.9mm
Inner Diameter74.4mm68.6mm - 76.3mm
Wall Thickness3.3mm2.8mm
Material7075-T6 Al2000 or 7000 series Al
(Source: SSCI, pp. 88;91;93)

Although the DIA analysts who attended the presentation found it "compelling", it seems unlikely that Joe convinced many in the IC. WINPAC did not publish a finished intelligence product based on Joe's research. Nobody did. Not even the DIA. Instead, DOE published an extensive eight-page Technical Intelligence Note on the Iraqi tubes. The paper refuted every argument Joe had made.

On August 17, 2001, the DOE published Iraq's Gas Centrifuge Program: Is Reconstitution Underway? Although the July `personnel' had claimed the tubes' specifications exceeded conventional weapons applications, the DOE had by now identified a non-nuclear end-use for the tubes: rocket motor cases. After the 1991 Gulf War, Iraq declared its possession of 160,000 high-strength aluminum tubes that had been intended for their Nasser-81 multiple rocket launch system (MRLS). The DOE paper pointed out that the dimensions and material of these tubes were an exact match for the tubes Iraq was pursuing in 2001.

The only specification that did not match exactly was the tolerances: the tolerances for the Nasser-81 were not as tight as the tolerances for the tubes. However, the DOE pointed out that the tolerances still were not tight enough for centrifuge rotors. In fact, they were looser than expected for an aluminum rotor "by factors of two to five" (SSCI, p. 92).

DOE also thoroughly explained why the tubes could not be used in a Zippe centrifuge without extensive modification. Zippe had designed a number of centrifuge rotors and the tubes did not match a single one of them. In particular, the tubes' walls were three times too thick. Contradicting Joe's presentation, the paper stated that all known aluminum rotors had a wall thickness of less than 1mm. (DOE analysts say that they explained this to Joe "many times" over the next two years and even went to the extraordinary length of asking Gernot Zippe himself.) The paper then went on to explore "various workable schemes to modify the tubes for favorable centrifuge rotor use." These included machining the inner and outer surfaces "up to and including re-melting the tubes and restarting...[the] fabrication process." (RS, p. 209).

Table 4 - Specifications of Iraqi Tubes, Nasser-81 Rocket tubes and Zippe-Type Rotors
Iraqi TubesNasser-81 RocketZippe 2.75"Zippe 3"Zippe 4"
Length900.0mm900.0mm280.0mm332.0mm500.0mm
Outer Diameter81.0mm
(+0/-0.1)
81.0mm
(+0.2/-0.2)
70.0mm76.2mm100.0mm
Inner Diameter74.4mm
(+0.1/-0)
74.4mm
(+0.1/-0.3)
68.6mm74.2mm98.0mm
Wall Thickness3.3mm3.3mm1.0mm1.0mm1.0mm
Material7075-T6 Al7075-T6 Al2000-T6 Al2000-T6 Al7000 S Al
(Source: Albright, 2003; Duelfer, 2004, vol. 2, p. 27)

DOE agreed with Joe that Gernot Zippe had used high-strength aluminum in his 1950s designs. However, Iraq in the late-1980s had built a Zippe centrifuge based on a design modified by the European company Urenco that had been developed in the early-1970s. The Zippe/Urenco designs used maraging steel and carbon fibre rotors, both of which are much stronger than aluminum. Maraging steel and carbon fibre can withstand much greater centrifugal force and so can be used in rotors with much larger diameters, almost twice the size aluminum allows. (Albright, 2003) So, not only would maraging steel or carbon fibre enrich uranium much faster than an aluminum rotor, but an aluminum rotor would be too small for the design the Iraqis knew how to build. (SSCI, p. 92) If Iraq did modify the tubes for use in a centrifuge cascade, it "would need to undertake its development program all over again and address each aspect of centrifuge engineering again at the reduced diameter and using the different rotor material." (SSCI, p. 92)

Table 5 - Specifications of Iraqi Tubes and Iraq's Zippe/Urenco Rotors
Iraqi TubesIraqi Maraging SteelIraqi Carbon Fibre
Length900.0mm620.0mm614.0mm
Outer Diameter81.0mm
Inner Diameter74.4mm145.5mm145.85mm
Wall Thickness3.3mm0.35mm1.0mm
Material7075-T6 AlMaraging SteelCarbon Fibre
(Blanks represent a lack of specific data. Source: Albright, 2003)

And so, by September, the matter had more or less been settled. There was no serious debate within the IC. One stubborn WINPAC analyst does not constitute a debate. No finished intelligence assessment based on Joe's research had been written. A plausible explanation had been found: the tubes were rocket motor bodies. The IC's experts had examined the tubes and concluded that they could only be used in a centrifuge if the Iraqis made extensive modifications. Even then, the Iraqis would only have rotors for a centrifuge they'd never built, had no parts for, and wouldn't work very well anyway. As one DOE analyst put it, if Iraq was really trying to make them into centrifuge rotors, "we should just give them the tubes." (SSCI, p. 113).

Were Joe and the `personnel' part of a WINPAC red team? If they were, it would explain a lot. It would explain why Joe's research wasn't written up as a finished intelligence product. It would explain his changing explanations, but not his conclusion. It would explain why the `personnel' assumed the Iraqis would abandon their successful centrifuge design for one that was untested and out-of-date.

Edited to add: I hate doing HTML tables!

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