When SWU met LEU: The Iran nuclear talks jargon A-to-Z

Drowning in a radioactive sea of nuclear jargon, mixing up Bushehr and breakout, plutonium and Parchin, centrifuges and code 3.1?
As Iran and six world powers negotiated Tuesday in Switzerland seeking to end the crisis over Tehran's nuclear programme, here is an A-to-Z glossary of the key technical terms:
A is for Arak
Until 2014, Iran was building a heavy water reactor at Arak. In theory, once operational, it could give Iran plutonium, the alternative to uranium for a nuclear weapon.
B is for Breakout
The time Iran would need, in theory, to make a bomb's worth of nuclear material. The powers want this "breakout time" extended to at least a year to give them time to react.
C is for Centrifuge
Machines that "enrich" uranium gas by spinning it at supersonic speeds, increasing the proportion of a fissile isotope, known as U-235, used for different purposes (see enrichment below).
D is for Downblending
Under a November 2013 interim deal (see JPOA below), Iran "downblended" its stock of uranium enriched to medium purities, diluting and converting it to another form.
E is for Enrichment
Natural uranium contains 0.7 percent of the isotope U-235. Enriched to 3.5-5.0 percent, it can be used for nuclear power reactors, 20 percent for nuclear medicines and 90 percent for a bomb. The process gets progressively easier.
F is for Fuel
Iran says its programme is to make fuel for 20 future reactors. Russia is contracted to fuel Iran's only existing plant, Bushehr, until 2021.
G is for Gachin
A uranium mine. The powers want to keep a closer eye on mines to ensure uranium is not being taken to secret enrichment sites.
H is for HEU
Around 1,000 kilogrammes of low-enriched uranium (LEU) are needed to make enough highly-enriched uranium (HEU) for one bomb, if further processed. Iran currently has some 8,000 kg of LEU.
I is for IAEA
The UN atomic watchdog, the International Atomic Energy Agency, keeps close tabs on Iran's nuclear activities and would have a beefed-up role under any deal.
J is for JPOA
The Joint Plan of Action, the November 2013 "interim deal" under which Iran froze certain nuclear activities in exchange for minor sanctions relief.
K is for Khan
Nuclear scientist Abdul Qadeer Khan, "father" of Pakistan's nuclear bomb, believed to have shared expertise with Iran.
L is for Light-Water
If Arak is changed to a light-water reactor, it will significantly reduce the amount of plutonium than could be extracted from the spent fuel.
M is for Missiles
Western powers want Iran's ballistic missiles programme to be covered under any deal, but Tehran does not.
N is for Natanz
Iran's main enrichment facility, with some 17,000 IR-1 centrifuges installed, including 1,000 faster IR-2M machines, but with a capacity of some 50,000.
O is for Oman
Oman was where Iran and the US held secret talks which dated back to 2012 and led to the current diplomatic effort.
P is for P5+1
The group of six powers negotiating with Iran: the US, Russia, China, Britain, France and Germany. All except Germany have nuclear weapons.
Q is for Qom
Iran's second main enrichment facility Fordo, near the holy city of Qom, is built into a mountain, making it virtually impregnable to military strikes.
R is for R&D
The powers want strict limits, or a complete stop, of Iran's research and development of newer, faster centrifuges.
S is for SWU
Separative Work Units -- a measure of the efficiency of centrifuges.
T is for TRR
The Tehran Research Reactor, originally supplied by the US, used to make nuclear medicines.
U is for UF6
Uranium hexafloride, the gaseous form of uranium for enrichment.
V is for Virtual Nuclear Weapon State
A country whose expertise and facilities put them on the threshold of being able to make nuclear weapons.
W is for Weaponisation
The work needed to be done to put uranium or plutonium in a bomb.
A stalled IAEA probe covers allegations Iran did research in this area -- the infamous "possible military dimensions" (PMD) file -- including at Parchin.
X is for Xenon
Can be used for testing centrifuges
Y is for Yellowcake
Processed uranium ore, then converted into uranium tetrafluoride and uranium hexafloride (see above). Not for eating, and not really yellow.
Z is for Zirconium
Metal used for cladding fuel rods in a reactor.
And ... 3.1
Modified Code 3.1, part of Tehran's contract with the IAEA, revoked by Iran. This, like the so-called Additional Protocol which Iran stopped implementing, allows for closer oversight.