Plutonium is very good for making a bomb. It does not need enrichment. Uranium has to be highly enriched for explosive purposes, and gas diffusion plants are so large that a terrorist would have to be quite an industrialist to build one. It is easier to steal plutonium. Breeder reactors make plutonium. Recycling nuclear waste also recovers plutonium and makes MOX. Places where plutonium is made or trans­ported have to be heavily guarded.

The development of gas centrifuges has posed a new problem [43]. These devices are relatively small and much more efficient. The separation factor is 1.2—1.5, compared with 1.004 in gas diffusion. Uranium has to pass through a cen­trifuge only 30-40 times before it reaches weapons grade. It would take many times more in gas diffusion. The uranium is in the form of UF6 in gaseous form. It has to be under partial vacuum so that it does not solidify and gum up the works. This means it cannot leak out. Centrifuges are small enough that a hundred of them can be installed in a building that looks like any other industrial building. Centrifuges can be connected in series so that the output of one goes into the next for further separation. A cascade of over 100 centrifuges can be designed to optimize the num­ber used at each stage of enhancement. One cannot prevent the construction of such a cascade for peaceful production of 5% U235 for power plant. The problem is that the cascades can be reconfigured in a few days to produce weapons-grade uranium. For instance, the output of 5% U235 from two-thirds of the cascades in a plant can be sent to the remaining one-third for further enrichment to 90% U235. The power used in either case is only about 160 W/m2, compared with 10,000 W/m2 in gas diffusion, so the clandestine activity cannot be detected by the power consumption, which is like that of any well-lighted building.

India and, in response, Pakistan were the first to use gas centrifuges. This is the reason for the recent attention given to Iran for its construction of an isotope separa­tion facility. The danger exists whether or not nuclear power is used for energy.