Why in News?

• Iran has announced that it has started up advanced uranium enrichment centrifuges in a breach of its undertakings under a troubled 2015 nuclear deal, days after the start of talks on rescuing the accord.

To know about the 2015 deal- JCPOA- https://officerspulse.com/iran-nuclear-deal-2/

Need for enrichment

• The nuclear fuel used in a nuclear reactor or for nuclear weapons needs to have a higher concentration of the U235 isotope than that which exists in natural uranium ore.  U235 when concentrated (or “enriched”) is fissionable.
• For nuclear weapons, enrichment is required from 80 to 90% or more which is known as Highly Enriched Uranium/weapons-grade uranium.
• For nuclear reactors, enrichment is required upto 3-5% which is known as Low Enriched Uranium/reactor-grade uranium.

How does a centrifuge work?

• Uranium is made up of two isotopes, the predominant uranium-238 (or U-238) and U-235, which is only 0.7% of natural uranium. It is the U-235 that can be directly split, or fissioned, to produce power in most of the world’s current commercial nuclear reactors. (Thus, materials like U-235 and plutonium are called “fissionable”.) The U-238 is not directly fissionable. To be useful, the concentration of U-235 must be increased as per needs.
• Several techniques have been used for enrichment but the preferred method is a gas centrifuge.
• The heart of a gas centrifuge is a tube, called the rotor that spins at high speed around its long axis. The performance of the centrifuge depends critically on the speed of the rotor. Today, rotors may spin in excess of 60,000 rpm with the outside surface of the rotor moving well in excess of the speed of sound.
• The spinning rotor creates powerful centrifugal forces that mimic a miniature gravitational field.
• In the spinning rotor, the slightly heavier UF6 that contains U-238 will be slightly more compressed along the rim relative to the lighter UF6 that contains U-235, which would have a relatively greater concentration near the axis. The separation between the two isotopes created by the centrifugal forces is quite small.
• No single centrifuge can achieve an adequate degree of enrichment and the amount of material that a single centrifuge can handle is small. To process sufficient material, centrifuges, sometimes hundreds, are operated in parallel.
• Each set of centrifuges enriches the uranium a bit more than the previous until the desired enrichment is achieved. Such a collection of centrifuges is called a cascade and any given set of centrifuges operating in parallel is called a stage.

Reference:

1. https://www.thehindu.com/news/international/iran-unveils-advanced-nuclear-centrifuges/article34291761.ece