SIMPLE, CONCEALABLE, AND MOBILE

Uranium, plentiful all over the globe and uncontrolled by any international treaties, is the starting point of the roads to both a plutonium and a uranium bomb. Uranium ore is milled and processed into "yellowcake," but the uranium in it has two isotopes: 99.3% is U 238, which is not fissile, and only 0.7% of U 235, which is. Since they are isotopes of the same element, they cannot be separated chemically, the difference in weight is the only way. This is quite difficult, since the ratio of masses, roughly 238/235 = 1.0128, differs only by about 1% from equality.

All enrichment processes start with turning the uranium into a gas, usually by combining it with fluoride to form uranium hexafluoride. The US bears the burden of the pioneer and still en-riches uranium by an outdated diffusion process, chosen during the Manhattan Project as the quickest realizable under pressing wartime conditions. It is based on the speed with which molecules of a gas diffuse through a porous membrane; that speed depends on their masses. The obvious solution, a centrifuge separator of the two components of the milk/cream type could not be used because at the time there was no material that would withstand the centrifugal stresses at the required rate of rotation. Today there are ultracentrifuges with up to 50,000 rpm (833 revolutions per second!). They make enrichment much cheaper and more effi-cient, and are used by most legitimate enrichers.

But these centrifuges are also well watched and recognizable. Thousands of stages are needed for high enrichment. The same centrifuges are used to enrich the output over and over again. Many hundreds of them can be used in parallel, but a small num-ber simply prolongs the time necessary to get the desired product. It is possible that Saddam has some ultracentrifuges, though it might not be easy to buy and ship a large number of them.

But there are other methods, at least two of which are more primitive even than the Manhattan Project Diffusion process. The one that I guessed Saddam would have chosen [AtE Mar 91] is the jet enricher, shown above. The gaseous UF6 (with helium added) enters a nozzle on the left and produces a high-speed jet, which is forced by a curved wall to go into a bend. The heavier molecules containing the U 238 atoms will experience a greater centrifugal force and will push more strongly against the wall, displacing the U 235 atoms toward the inner curve. A knife edge then separates the heavy (depleted) fraction from the light (enriched) one. This will not, of course, work in one pass, and the lighter fraction has to be piped back into the input nozzle for many further transits through the device. Other versions of the same principle have been proposed (e.g., a meandering pipe depositing the heavier fraction in the alternately right and left bends). The device is comparatively simple and small, and any number of jets can work separately in many places. The uranium shipments to one or more central depots can proceed at night far more easily than those of SCUD missiles, whose nocturnal transportation the US air force was not able to spot.

It is still my guess that this is one of the methods he has been using. Shipments of calutrons were intercepted by British and US intelligence, but they only noticed at the last moment that thick 120 ft metal pipes were being cast for him in Britain; they were intended to be barrels for giant guns. With intelligence services reduced to satellite photos and short of human agents (who would be fool enough to risk his life for a service meticulously supervised by such a tight-lipped and trustworthy institution as the US Con-gress?), no one can tell how many jet enrichers Saddam has built and safely stacked away. They can be shipped in inconspicuous components, if not built domestically.

Ah, but the State Department is hot on his trail. Iraq has no power reactors, has admitted to using three methods of enriching uranium, and is known to have highly enriched uranium, which has no other uses than bombs (about 50 to 55 lbs for one). This made the State Department's semiliterate Margaret Tutwiler proclaim (7/9/91) "Furthermore, the extent of Iraq's program, along with infor-mation we have from numerous sources makes us believe strongly that Iraq has a program to develop nuclear weapons."

A brilliant deduction amidst this tantalizing uncertainty.

Meanwhile North Korea is shipping more than 300 Scud C mis-siles, adapted for chemical warheads, with double the range, three times the payload, and several times the accuracy of those showered on Israel, to US ally Syria, all paid for and approved by US ally Saudi Arabia.