I read about this before, thus I never quite understood why they should export their own uranium to Russia for enrichment. And of course, why shoulden't they use their own uranium?

Indeedy, it would change the equation a bit.

Below, estimates of fuel tonnage and yearly reactor loads (25t/yr) depending on mining resources (20,000t / 30,000t) and tail assay (0.35% / 0.25%).

Mined U3O8 (t)	3,000	20,000	30,000
Mined U Metal (t)	2,544	16,960	25,439
Tail 0.35% - Fuel 3.6% (t)	290	1,930	2,896
Tail 0.25% - Fuel 3.6% (t)	360	2,379	3,569
Tail 0.35% - Yr load (25t/load)	12	77	116
Tail 0.25% - Yr load (25t/load)	14	95	143

A typical 1,000 MWe PWR reactor runs for about 50 years and requires ~100t of fuel on the first year (initial load) then 25t each year for refuelling. That amounts to 1325t over the life of the reactor. So depending on the assumptions (resources/tail assy), Iran can supply the life time load of 1 to not fully 3 reactors.

An other, more reasonable way to look at it is, assuming Iran builds 6 reactors, Iran can supply the initial load of those reactors then keep them running them anywhere between 10 and 21 years. After that, they need to find new resources with lower grade ore (which I assume to be feasible). But then, you come back to the issue of the crappy separative capacity of their centrifuges and the (ir)rationality of their current investment in obsolete technology. They would need to install 200,000 to 300,000 of their P1-like centrifuges to support the yearly reload of 6 reactors. Divide that number by 2 assuming a more advance P2-like design with a rotor made of maraging steel.

For reference and comparison of separative capacity of various centrifuge designs:

Machine	Capacity (kgSWU/yr)	Notes
Pakistan/Iran P1	~ 2 to 3	Decommissioned by Pakistan?
Pakistan/Iran P2	~ 5 to 6	Iran has blueprints, but real machines?
Urenco TC12	40	In operation since early 90s - Decommissioning
Urenco TC21	> 200	In production ramp-up
USEC AC	> 300	Pilot plant 2006

Pakistani designs are a throwback from the 60s, hopelessly obsolete.

Yes, it was central to his argument that controlling the full nuclear cycle would be economic insanity.

_{*Lunatic*, n.
One whose delusions are out of fashion.}