As Iran and six world powers negotiate in Switzerland on ending 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 ******. B is for Breakout The time Iran would need, in theory, to make a worth of nuclear material. D is for Downblendin Under a **vember 2013 interim deal (see JPOA below), Iran "downblended" its stock of converted uranium enriched to medium purities to low.