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Mahesh

12/03/24 21:59 PM IST

Nuclear waste

In News
  • Recently, India loaded the core of its long-delayed prototype fast breeder reactor (PFBR) vessel, bringing it to the cusp of stage II — powered by uranium and plutonium.
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 of Nuclear waste
  • It is hot and radioactive, and needs to be kept underwater for up to a few decades.
  • Once it has cooled, it can be transferred to dry casks for longer-term 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.
  • Nuclear power plants also have liquid waste treatment facilities.
  • Liquid high-level waste contains “almost all of the fission products produced in the fuel”. It is vitrified to form a storable glass.
Control measures
  • 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.
  • Importantly, reprocessing also yields weapons-usable (different from weapons-grade) plutonium.
  • The IAEA has specified eight kilograms of plutonium in which plutonium-239 accounts for more than 95% to be the threshold for “safeguards significance”. It tightly regulates the setting up and operation of these facilities as a result.
How India handle nuclear waste?
  • According to a 2015 report of the International Panel on Fissile Materials (IPFM), India has reprocessing plants in Trombay, Tarapur, and Kalpakkam.
  • The Trombay facility reprocesses 50 tonnes of heavy metal per year (tHM/y) as spent fuel from two research reactors to produce plutonium for stage II reactors as well as nuclear weapons.
  • Of the two in Tarapur, one used to reprocess 100 tHM/y of fuel from some pressurised heavy water reactors (stage I) and the other, commissioned in 2011, has a capacity of 100 tHM/y. The third facility in Kalpakkam processes 100 tHM/y.
  • The IPFM report also said the PFBR’s delays suggested the Tarapur and Kalpakkam facilities “must have operated quite poorly, with a combined average capacity factor of around 15%”.
  • If and when the PFBR starts functioning and spent fuel from it is discharged, that will bring its own complications because it will have a different distribution of fission products and transuranic elements.
Source- The Hindu

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