>
> There is a formula for measuring the potential purity
> output per unit input of gas centrifugation given in
> separative work units (SWUs). For example 3.5% U-235
> purity requires 4.3 SWUs. Weapons grade or 90% U-235
> requires 4,600 SWUs.
Since I first heard that infuriating government howler the other day about "enough highly-enriched Uranium for a warhead in sixteen days" (those sons-of-bitches, how I hate them, they really _do_ hate science, that's _obviously_ off by whole orders of magnitude, I take it as a deliberate effort to piss off those of who know enough physics to flinch, rubbing it in our face that we're outnumbered ten-to-one by iggerint rubes who'll believe their hogwash like it was Gospel) I've been poking around, trying to find the exact throughput in SWUs-per-day of a single Pakistani P-1 or P-2 centrifuge. While I still don't have that specific figure tacked down, so I can't tell you yet whether that White House's wild, nakedly fraudulent claim is off by a factor of a hundred or by a factor of ten thousand, I've learned is that it doesn't exactly make sense to say that to separate the twenty or so kilograms of highly enriched Uranium (HEU)required for your basic entry-level nuclear bomb would require precisely _n_ SWU; the number of SWUs required would vary considerably with the percentage of U235 remaining in the tail. If I'm applying this formula
http://www.sizes.com/units/separative_work_unit.htm
correctly it seems you start with natural uranium and you purify out a seventh of it to 85% HEU - that is, you start with 0.7% U235 and the depleted Uranium left over is 0.6% - to get 20 kg of HEU you need to apply about 3300 SWUs of effort to 20000 kgs of natural Uranium. But if you want to extract five-sevenths of the U235 in your supply of natural Uranium, so the depleted Uranium is only 0.2% U235, you'd need to apply 5100 SWUs to only 4000 kg of natural Uranium. So for a country in a hurry to get their first few nuclear cores, assuming they have a fairly large supply iof yellowcake, they can cook up the HEU for the first few bombs somewhat cheaper and quicker than the HEU for later ones when they're squeezing a larger percentage of U235 out of their supply of natural Uranium.
Yours WDK - WKiernan at ij.net