I can't find anything written about what efficiency means, but...

I can't find anything written about what efficiency means, but I'd assumed that it worked like this (because this is how factors normally would work):

(Normal uranium is about 0.7% enriched and to use it in a normal reactor you need to be about 3%-5% enriched, which is a target of about 800% enrichment).


A factor of 1 means that your process does nothing to the uranium (its still at 100% of its original enrichment).  A factor of 1.01 (gaseous diffusion) means that to get to 800% you will need to run your process about 200 times (due to compound interest its not 700 times).  I think that's what they call a cascade where the one plant does the gaseous diffusion stuff multiple times in a row.  If you have a factor of 1.25 (centrifuge) then that's 25 times better than a 1.01 enrichment.  With a 1.25 plant you need to run the process about 8 times to get to 800%.  However even if we have a factor of 2 then we run the process 3 times (and obviously a factor of 8 or higher would mean we only run the process once).

It gets a little more complex because when you have run a few rounds of enrichment and are half way to your goal you have ended up with your enriched uranium, and some low % tails.  You can start to ignore the tails and focus on only enriching the higher % uranium, which decreases your cost.  Of course if uranium is expensive or your enrichment process has a high factor and is cheap then you can continue to use your tails for longer.  Tails often have 0.2% rather than 0.7% in natural uranium, so that's light work for a process with efficiency of 3 or 4, but a lot of work for centrifuges.

Google won't give me anything better as supporting evidence though - the best I could find was https://en.wikipedia.org/wiki/Enriched_uranium, which says that "centrifuges are a factor of 20" [times more efficient than gaseous diffusion plants].  Which is consistent with the difference between 1.01 and 1.25 (remember compound interest).

Does anyone know for sure how this works?