Context

In a breach of the 2015 nuclear deal, Iran claims that it has resumed 20 percent uranium enrichment at Fordow site where activity was banned for 15 years.

About

• What is Uranium enrichment?
• Uranium found in nature consists largely of two isotopes, U-235 and U-238. 
• Enriched uranium is produced by feeding uranium hexafluoride gas into centrifuges to separate out the most suitable isotope for nuclear fission, called U-235.
• Low-enriched uranium, which typically has a 3-5% concentration of U-235, can be used to produce fuel for commercial nuclear power plants.
• Highly enriched uranium has a concentration of 20% or more and is used in research reactors. Weapons-grade uranium is 90% enriched or more.
  

The deal Under the 2015 nuclear deal, Iran is allowed to enrich uranium only up to a 3.67% concentration to stockpile no more than 300kg (660lbs) of the material to operate no more than 5,060 of its oldest and least efficient centrifuges to cease enrichment at the underground Fordo facility Another part of the deal instructs Iran not to accumulate more than 130 tonnes of heavy water, which contains more hydrogen than ordinary water, and to redesign its heavy-water nuclear reactor at Arak. Spent fuel from a heavy-water reactor contains plutonium, which can be used in a nuclear bomb.

The concern

• The move is seen as a significant step toward achieving weapons grade levels of uranium. 
• The higher levels raise fears that Iran will work toward building a nuclear weapon, which requires 90% enrichment.
• Iran’s move is its latest away from the nuclear deal as it seeks to pressure the other signatories, particularly those in Europe, to deliver on promises of sanctions relief. 
• The United States pulled out of the deal in 2018 and instituted economic sanctions, especially targeting Iran’s key oil sector.