If operated on a large enough scale (perhaps 10 bombs-worth per year), an energy-inefficient enrichment technology such as EMIS or gaseous diffusion might be detectable by its heat emission. At Iraq's A1-Tarmiya facility, for instance, heat rejection into the air or, as appears to have been planned, into the Tigris river, might well have been observable once operation had begun. However, at lesser production rates or with more efficient technologies (e.g., centrifuges, or EMIS techniques that employed permanent magnets and lower beam-voltages), heat signatures would be less evident. Heat emission is a nonspecific signature, however, that would be most useful for monitoring the startup and shutdown patterns of known facilities; it would have to be combined with other indicators to determine whether a given unknown facility were nuclear-related. If the heat were dischmged into a modest-sized river, a resulting rise in temperature on the order of O.1"C or more (depending on flow-rate, mixing, etc.) would be detectable in the far-infrared. Alternatively, heat from the cooling towers might also be detectable.
A potential sign of a clandestine enrichment or other nuclear facility could be unexplained special security or military reinforcements around an industrial site. These arrangements might be visible from overhead or from the ground. At close enough range, other signatures would become observable. For example, even a very small centrifuge plant might emit detectable acoustic or radiofrequency noise, and the pulsed lasers used for laser isotope separation emit characteristic electromagnetic signals at kilohertz frequencies that might be detected. Samples of substances taken from either declared or suspect facilities could also indicate their potential for producing weapon materials. For example, UCL4 or other uranium chloride combinations could indicate EMIS or Chemex enrichment technology, and U F6, UF4, HF, or uranium metal could indicate other uranium enrichment techniques. Analysis of environmental samples containing depleted or enriched uranium in water or soil would also provide very important signatures.
Patterns of foreign procurement of essential materials and parts, such as newer high-strength materials or maraging steel (a very high-tensile-strength steel used to manufacture some types of gas centrifuge), or large iron electromagnets, high-voltage power supplies, and large vacuum systems (for EMIS), might also help to indicate a county's intentions.
An indigenous uranium mining industry might provide early indication of a clandestine uranium or plutonium-based weapon program and is a sure indicator of at least the possibility.
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