FACTBOX: Iran's nuclear activities

(Reuters) - Iran has told big powers it will enter no more "condescending" talks meant to scrap its nuclear program but wants to negotiate a broader peace and security deal, according to an Iranian letter leaked on Tuesday.

Here are some details about Iran's nuclear program:

* BACKGROUND

-- Iran says it wants to build nuclear power plants so it can maximize exports from oil and gas reserves, the world's second largest. The West suspects Tehran is seeking the capacity to make nuclear bombs since it is enriching uranium but without power plants to use such fuel.

-- Russia is working to complete Iran's first, and so far only, nuclear power plant, begun before the 1979 Islamic revolution, at Bushehr on its southwestern Gulf coast. It is designed to run only on Russian-produced fuel, according to a senior Western official in the Middle East.

-- In 2002, an exiled Iranian opposition group revealed the existence of the underground Natanz facility in central Iran to enrich uranium, a process that can yield fuel for power stations or, if highly refined, material for nuclear warheads.

* BUSHEHR:

-- Construction of two pressurized water nuclear reactors began in 1974 with German and French help. The two complexes were partially built before the 1979 revolution, when Western partners withdrew and the project was frozen.

-- A Russian contract to resume construction was signed in 1995. Iran says Bushehr will be part of a power plant network planned to produce 20,000 megawatts by 2020. It says it intends to launch test runs at Bushehr later this year.

* ISFAHAN:

-- Iran's uranium ore processing plant at Isfahan, some 400 km (250 miles) south of Tehran, converts the mineral into hexafluoride gas, the form that is fed into centrifuge machines for enrichment into nuclear fuel.

-- A nuclear technology and research centre in Isfahan is Iran's largest, employing up to 3,000 scientists.

-- The processing site is under regular inspection by the U.N. nuclear watchdog, the International Atomic Energy Agency.

* NATANZ:

-- In the desert 230 km (140 miles) south of Tehran, a vast subterranean hall contains some 3,600 centrifuges enriching uranium, more than 10 times the number spinning two years ago. Output remains well below industrial capacity -- making fuel in usable quantities -- but is gradually rising.

-- Nearby is the above-ground pilot wing of Natanz where Iran is testing advanced models of centrifuges able to refine uranium 2-3 times faster than its current 1970s-era model. Iran aims eventually to operate more than 50,000 centrifuges in the underground plant to achieve industrial-scale enrichment.