By Francois Murphy
VIENNA, Feb 26 (Reuters) - The United States hopes talks with Iran in Geneva will produce an agreement to prevent Tehran acquiring nuclear weapons, and President Donald Trump has amassed forces in the Middle East to increase pressure on the Islamic Republic to reach a deal.
WHAT IS AT STAKE?
Iran has over decades developed an advanced and large-scale uranium enrichment programme. While enriched uranium can be used as fuel in power plants at various purity levels, at high levels it can be used to
make nuclear weapons.
Until Israel and the U.S. attacked its nuclear facilities last June, Iran was enriching uranium to up to 60% purity, a short step from the roughly 90% that is weapons grade.
It had enough material enriched to that level, if enriched further, for 10 nuclear weapons, according to an International Atomic Energy Agency yardstick, and more at lower levels.
The IAEA, the U.N. nuclear watchdog, has not, however, been able to verify how much of that uranium stock remains. Iran has yet to declare what happened to it or allow the agency to inspect its bombed nuclear facilities.
Iran's enrichment plants were destroyed or badly damaged in the attacks though their exact status, like that of the uranium stock, has yet to be verified.
WHAT DO BOTH SIDES WANT?
After the June bombings, the two sides expressed incompatible demands: the U.S. said it wanted Iran to give up enrichment, and Iran said it would never do that.
As a party to the nuclear Non-Proliferation Treaty, Iran has the right to enrich uranium as long as it does not use it to produce nuclear weapons, which it says it would never do.
While an agreement might include an initial phase in which Iran suspends enrichment, there are limited options in terms of what any deal might let it do with its enrichment programme:
* Enrich elsewhere
In previous rounds of talks the idea was floated of a regional enrichment consortium, which would involve setting up a joint venture outside Iran with one or more other countries from the Middle East. Tehran has always rejected that as an alternative to enriching on its soil.
* Enrich for other purposes
Centrifuges, the machines that enrich uranium, can be used for other purposes, such as the production of so-called stable isotopes, which have a range of applications in medicine and scientific research.
The landmark 2015 deal between Iran and major powers, which Trump pulled the U.S. out of in 2018, allowed centrifuges at Iran's underground Fordow site to be used only for the production of stable isotopes.
One retaliatory step by Iran after Trump's withdrawal was to start enriching uranium at Fordow, which the U.S. bombed in June.
* Enrich to a low level
It becomes exponentially easier to enrich to weapons-grade the more highly enriched uranium you start with is. In terms of effort, once you have enriched to 5% purity you are more than halfway to weapons grade.
Keeping Iran at arm's length from being able to race towards nuclear weapons will involve limiting the purity it can enrich to and how much enriched uranium it can amass.
The 2015 deal let Iran enrich to 3.67% purity. Diplomats have said only half-jokingly that Trump's rejection of that deal is so great that 3.67% is the one enrichment level he will not accept now.
WHAT ELSE NEEDS TO BE ADDRESSED?
Any deal would also have to require thorough accounting for Iran's stock of enriched uranium. Any doubts about that could trigger a new conflict.
As in 2015, a deal would most likely require the dilution or removal of enriched uranium, and limit the number of centrifuges and where they can be used.
Since Iran knows how to enrich with advanced centrifuges, and has an unknown number of those centrifuges stored at unknown locations, the risk of it enriching in secret could hang over any future deal. That makes verification, most likely by the IAEA, a central issue.
(Editing by Timothy Heritage)
