TCS Daily


Centrifugal Force

By Ralph Kinney Bennett - July 12, 2004 12:00 AM

Iran is determined to build a nuclear bomb.

At present we must endure the familiar slow dance of warnings, denials, speculations, denials, revelations, denials, etc., etc., until the inevitable day when headlines announce the new member of the nuclear club.

The key is how quickly Iran can acquire or produce the highly enriched fuel necessary to produce effective nuclear weapons. It is buying nuclear power plant fuel (enriched 3 to 5 percent with uranium-235) from Russia, but acquiring weapons grade uranium (enriched 20 to 90 percent) is a little more difficult.

But Iran is also working and spending prodigiously to produce enriched uranium on its own. This enrichment program centers on how quickly Iran can build the tens of thousands of centrifuges necessary to separate the rare U-235 isotope from uranium hexafluoride gas (UF6). These centrifuges are costly, complex, precision-made devices incorporating exotic materials such as super strong maraging steel. It takes years to build them in sufficient numbers, test them adequately and marshal them into the precisely plumbed formations (called cascades) that can safely and efficiently produce significant amounts of enriched uranium.

A typical "cascade hall" is a vast room, its concrete floor filled with what would appear to be thousands of gleaming new stove pipes stacked vertically side-by-side in long rows. Each of these slim metal cylinders, about six-and-a-half feet tall and the approximate girth of a telephone pole, is a vacuum chamber containing within it another cylinder called a rotor tube.

At the bottom of each inner cylinder is an electric motor, which turns the rotor tube at tremendous speeds. This inner rotor tube itself is balanced on a single friction point -- a small lubricated "needle" bearing. A series of ring magnets holds the top of the tube in place. Thus, these ingenious devices rotate in an almost friction-free environment at speeds around 1500 revolutions per second.

They run so fast and create such centrifugal force that they actually flex like bow strings along their axes (special joints or "bellows" on the rotor tubes control this flexing). These centrifuges, using relatively little electrical power, can run continuously for a decade with no maintenance. Vast banks of interconnected centrifuges, tens of thousands of them, run night and day slowly producing small amounts of enriched U-235.

The tremendous centrifugal force pushes heavier gas molecules (U-238) out to the walls of the rotor tube, while the lighter U-235 molecules tend to collect close to the shaft at the center. This lighter stream of U-235 is drawn off, joining the streams from thousands of other centrifuges to slowly build a supply of enriched gas that can eventually be incorporated into nuclear fuel or -- at advanced stages of enrichment -- fissile material for weapons.

At a secret facility near the Iranian city of Natanz, the Tehran government is building a series of vast cascade halls, designed to eventually hold 50,000 or more centrifuges. Iran is going to the trouble of building these cascade halls underground in thickly walled steel reinforced concrete buildings, an attempt to protect them from aerial attack. Even the underground entrance tunnels to these buildings have been designed with a series of baffles to protect against the direct entry of "smart bombs" or cruise missiles.

The "hardening" of the Natanz facility is further evidence that Iran learned long ago the lesson of Osirak. Iraq's Osirak nuclear reactor was the heart of that nation's Tuwaitha Nuclear Center, on the outskirts of Baghdad, when the Israeli Air Force destroyed it in a daring raid back in 1981. The raid set back Iraq's nuclear weapons program and forced it to begin dispersing its nuclear assets to sites throughout the country.

In fact, the ambitious building project at Natanz, about 90 miles north of Isfahan, is just the latest known addition to Iran's large and sophisticated nuclear facilities. There is a large underground nuclear facility, including uranium enrichment, hidden deep in the Albroz Mountains just north of Teheran. What was once a backward mountain village, Moallen Kalayeh, near the site, is now home to hundreds of scientists, technical experts and security people.

Some intelligence reports indicate that in addition to centrifuge separation work at Moallen Kalayeh, Iranian scientists are working with a more exotic but potentially safer, faster and more productive method of uranium enrichment involving AVLIS (atomic vapor laser isotope separator). AVLIS equipment was reportedly shipped to Iran by Russia a year ago.

This advanced system, first developed at the U.S. Lawrence Livermore National Laboratory, uses a precisely tuned laser beam to search out U-235 isotopes in a stream of vaporized uranium passing through a vacuum chamber. The "optically excited" U-235 isotopes are then separated and collected.

After authorizing a plant scale AVLIS system to show sustained performance, the United States Enrichment Corporation (USEC), the government-created but now privatized company that oversees all U.S. uranium enrichment programs, canceled the program for economic reasons in 1999. Russia, however, continued to develop and refine its own AVLIS system -- the one reportedly sent to Iran.

(It is interesting to note that the United States has never used the centrifuge method of uranium enrichment, but has relied on the old, slow, but proven method of gaseous diffusion at two large plants in Piketon, Ohio, and Paducah, Kentucky. However, the U.S. is now planning to build two pilot centrifuge cascade plants at Piketon and at Eunice, New Mexico.)

In addition to the underground cascade halls at Natanz, there are other buildings in more advanced stages of construction where new centrifuges will be assembled and tested using components made at sites scattered throughout Iran. The assembly of centrifuges is an exacting and complicated process. The International Atomic Energy Agency (IAEA) reports that a pilot plant of 160 centrifuges in a small cascade has been in operation at Natanz for more than a year. IAEA officials reportedly saw the components for 1000 more centrifuges at the same location.

Cascades of the size being built at Natanz are an immense undertaking of a sophistication difficult for the average person to grasp. Only a dozen nations have the wherewithal to undertake such a program. Japan, for instance, continues to have great difficulty in building and operating large-scale centrifuge cascades despite its renowned technological capabilities.

Iran claims that it needs plants the size of Natanz to provide low-enriched fuel for the nuclear reactors it plans to build in order to supply the country with 6,000 megawatts of electricity. If the Natanz plants were operating full out with 50,000 centrifuges, say some experts, they would provide not quite half of the fuel necessary for the contemplated power reactors. Iran is buying low-enriched fuel from Russia to augment its needs, but there may well be other large cascade facilities under construction.

The significance of such large centrifuge plants is this: A relatively small fraction of such a plant's centrifuges, say 5000, could be used to produce enough highly enriched uranium to build three or four weapons a year. Dr. David Albright, of the Institute for Science and International Security, notes that "if a country can make an enrichment plant of this size, it can make enough machines to outfit another secret enrichment plant" for nuclear weapons. Given the present restrictions Iran has placed on IAEA inspectors, such a plant would be impossible to detect.

Perhaps one is already in operation.

Any expansion of the nuclear club must give one pause. But the fact that the government of Iran is the true center of an anti-Western, Jihadist (if you will) movement of a peculiarly corrosive and hate-filled nature, makes its fixation on the acquisition of nuclear weapons all the more troubling...and dangerous.


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