Context:
Recently, India loaded the core of its long- delayed prototype fast breeder reactor (PFBR) vessel.
Background: –
Large-scale use of nuclear power is accompanied by a difficult problem: waste management.
About Nuclear Waste: –
- In a fission reactor, neutrons bombard the nuclei of atoms of certain elements. When one such nucleus absorbs a neutron, it destabilises and breaks up, yielding some energy and the nuclei of different elements.
- For example, when the uranium-235 (U-235) nucleus absorbs a neutron, it can fission to barium-144, krypton-89, and three neutrons. If the ‘debris’ (barium-144 and krypton-89) constitute elements that can’t undergo fission, they become nuclear waste.
- Fuel that is loaded into a nuclear reactor will become irradiated and will eventually have to be unloaded. At this stage it is called spent fuel.
- The spent fuel contains all the radioactive fission products that are produced when each nucleus breaks apart to produce energy, as well as those radioactive elements, produced when uranium is converted into heavier elements following the absorption of neutrons and subsequent radioactive decays.
- Handling the spent fuel is the main challenge: it is hot and radioactive, and needs to be kept underwater. Once it has cooled, it can be transferred to dry casks for longerterm storage.
- All countries with longstanding nuclear power programmes have accumulated a considerable inventory of spent fuel. For example, the U.S. had 69,682 tonnes (as of 2015), Canada 54,000 tonnes (2016), and Russia 21,362 tonnes (2014).
- Depending on radioactivity levels, the storage period can run up to a few millennia, meaning they have to be isolated from human contact for periods of time that are
longer than anatomically modern Homo sapiens have been around on the planet.
How is nuclear waste dealt with?
- Once spent fuel has been cooled in the spent-fuel pool for at least a year, it can be moved to dry-cask storage, and is placed inside large steel cylinders and surrounded by an inert gas. The cylinders are sealed shut and placed inside larger steel or concrete chambers.
- Reprocessing — the name for technologies that separate fissile from non-fissile material in spent fuel — is another way to deal with the spent fuel. Here, the material is chemically treated to separate fissile material left behind from the non-fissile material. Because spent fuel is so hazardous, reprocessing facilities need specialised protections and personnel of their own. Such facilities present the advantage of higher fuel efficiency but are also expensive.
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