Iran's putative nukes as much as the those in the hands of the USA's own fundamentalist madmen, either.

...falls in line with my information. Scott Ritter seems to think most of the hysteria is just that and far from the truth.

...(Separative Work Unit). An online calculator can be found here:
link.

The important thing to remember is that with each "pass through the cascade" as you express it above, the number of SWUs required for the desired level of enrichment decreases [decrease in the amount of material that runs through the cascade each cycle as the tails for the previous round are taken off].

Number of SWUs required to enrich 1 tonne of natural hex (0.71% U235) to 3.3787663% [6 "passes through the cascade" assuming enrichment factor of 1.3 and starting enrichment of 0.71%]: 371.02, producing 0.133 tonnes of enriched hex [assumes tails of 0.3, which is the calculator's default] - I manually entered the figures for the repeat stages in the calculator and the total for the 6 runs and the one step reported total match

Number of SWUs required to enrich 1 t natural hex to 90% [18+ "passes through the cascade"]: 596.74, producing 0.05 tonnes of enriched hex assuming same tails of 0.3 - did not manually enter the figures for the repeat runs; too much to do today - if the reader wishes to do it, I leave it to them

“The absence of any US-Iran bilateral channel...may have the perverse effect of reinforcing Iranian interest in progressing in the nuclear realm so that the US will be forced to take it seriously and engage it directly." ~ Richard Haass

;)

...is that the folks that Russ has cited have it right. SWU [or Sleep Inducing Technical Term in Russ' piece above ;)] is the unit used to measure centrifuge output.

“The absence of any US-Iran bilateral channel...may have the perverse effect of reinforcing Iranian interest in progressing in the nuclear realm so that the US will be forced to take it seriously and engage it directly." ~ Richard Haass

No, Separative Work Unit is not - repeat not - the measure of centrifuge output. It's the COST of actually conducting the concentration. That's a big difference. Here's the definition from the EIA:

"Separative work unit (SWU): The standard measure of enrichment services. The effort expended in separating a mass F of feed of assay xf into a mass P of product assay xp and waste of mass W and assay xw is expressed in terms of the number of separative work units needed, given by the expression SWU = WV(xw) + PV(xp) - FV(xf), where V(x) is the "value function," defined as V(x) = (1 - 2x) 1n((1 - x)/x)."

Note that expression "... effort expended..." That's the cost of doing the work, not the level of difficulty. I would concede that it does imply that the time required to perform the concentration to HEU levels will be shorter than that required to achieve LEU levels.

...I meant the "work" of spinning the thing not anything to do with the characteristics of the enrichment product. I don't think that "cost" is a great term for describing it either, unfortunately, given that one can trade off various forms of cost in the process (raw material inputs vs. SWUs).

I guess that's why they used such a sleep inducing technical term as SWU, to steal a phrase.

“The absence of any US-Iran bilateral channel...may have the perverse effect of reinforcing Iranian interest in progressing in the nuclear realm so that the US will be forced to take it seriously and engage it directly." ~ Richard Haass

"Work" and "cost" mean the same thing in this context. The concept of a Separative Work Unit was clearly created to offer a normalized unit which can be used to assess the "work" of processing unenriched uranium to a certain level of concentration. It appears to be used by the nuclear power industry to assess what the costs will be to process uranium for fuel. If you know how much "work" needs to be done, by evaluating the price for work ($ per Kw-hr for power, $ per labor-hour, $ per rental-hour for the equipment), one can develop an understanding of the cost to reach certain purities.

What the concept does show is that the time required to achieve a certain level declines, so long as one is looking at processing only a fixed quantity of material. This is done because the quantity of material to be processed to a final state declines, as you've pointed out earlier. That enables the processor to reassign the equipment to expedite the process rate. Just looking at the examples we've been discussing, it would mean that after the producing the LEU with, lets say 6000 centrifuges, the cascade needs fewer centrifuges to process the remaining material. That offers the possibility of splitting the total 6000 centrifuges into different process lines, thereby accelerating the final production process to achieve HEU.

...great generic term here because the decision making surrounding the whole process is about balancing different forms of cost (hex consumption vs. SWU consumption). Seems to me to be the same sort of imprecision as when using the term "output" to describe the number of SWUs that a given cascade or centrifuge can produce over a given period. Though "output" is used in this context (particularly in the grey literature), as you've properly noted it isn't a great idea.

“The absence of any US-Iran bilateral channel...may have the perverse effect of reinforcing Iranian interest in progressing in the nuclear realm so that the US will be forced to take it seriously and engage it directly." ~ Richard Haass