The position outlined by Iranian nuclear agency head Ali Akbar Salehi appeared to be the most detailed yet of what Tehran wants at its closed-door negotiations with six world powers. It also highlighted the huge obstacles in the way of an agreement by a July 20 target date, since the world powers want Iran to reduce its enrichment program.
Iranian Foreign Ministry spokesman Marzieh Afkham said "substantial differences" remained.
Depending on its level, enriched uranium can be used for reactor fuel or the core of a nuclear weapon. Iran says it does not want such arms.
It went into nuclear talks last year with more than 9,000 centrifuges enriching uranium and about 10,000 on standby. The U.S. is ready to accept only a fraction of that number or even less, if Tehran insists on newer machines with a higher output. And it wants the enrichment program frozen at that low level for decades.
But Salehi told Iran's official IRNA news agency his country wants to expand the output of its enrichment program over the next eight years to a level that would need about 190,000 current centrifuges. Salehi said Iran wanted to use 8,000 advanced models to achieve that goal.
He also said Iran can envisage re-engineering its underground Fordo site as an enrichment research and development facility; as an isotope production unit, a suggestion he said was made by Russia, or as a physics and space radiation laboratory.
The first two options are linked to enrichment. That's something the U.S. has ruled out at Fordo, because it is dug into a mountain and impervious to air attacks in case it is used to make weapons.
Russia, China, Britain, France and Germany are also at the Vienna talks.