Nuclear Waste

Why in the 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 — of its three-stage nuclear programme.
• By stage III, India hopes to be able to use its vast reserves of Thorium to produce nuclear power and gain some energy independence.

• But the large-scale use of nuclear power is accompanied by a difficult problem: waste management.

What is Nuclear Waste?

• Radioactive waste is a type of hazardous waste that contains radioactive material and its byproducts.
• Radioactive waste is a result of many activities, including:
  • Nuclear medicine
  • Nuclear research
  • Nuclear power generation
  • Spent fuel rods
  • Nuclear decommissioning and dismantling
  • Rare-earth mining
  • Nuclear weapons reprocessing

Generation of Radioactive byproducts

• They are generated as a result of nuclear fission.
  • 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.

Spent fuel rods

• Fuel loaded into a nuclear reactor will become irradiated and eventually have to be unloaded.
• At this stage, it is called spent fuel.
• Spent fuel rods after energy production contains radioactive isotopes.

Examples of Nuclear Waste

• Argon 41
• Radioiodine
• Cobalt-60
• Strontium-90
• Tritium 
• Caesium-137

Nuclear waste is highly radioactive and needs to be stored in facilities reinforced to prevent leakage into and/or contamination of the local environment.

What are the types of Nuclear Waste?

High-level waste (most dangerous)

• Spent fuel rods, liquids from reprocessing fuel.
• Needs isolated storage for thousands of years.
• It is primarily uranium fuel that has been used in a nuclear power reactor and is “spent,” or no longer efficient in producing electricity.
• This includes radioactive isotopes of lighter elements such as cesium-137 and strontium-90. These isotopes, called “fission products,”. 

Intermediate-level waste

• Filters, cladding from fuel rods, reactor components.
• Requires careful management.

Low-level waste (least dangerous)

• It includes items that have become contaminated with radioactive material.
• Examples: Protective clothing, tools with low radiation contamination, shoe covers, wiping rags, filters, etc.
• These are disposable in shallow burial sites.

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What happens to the Nuclear Waste?

• Spent fuel rods are still highly radioactive and hot due to residual decay heat.
• They are initially stored in water pools inside the reactor facility for several years to allow them to cool down.
• After cooling, they are transferred to dry cask storage on-site.
  • These casks are heavily shielded containers designed to safely store spent fuel rods for decades.

How can Nuclear Waste be disposed of?

Shallow Burial

• Low-level waste, with minimal radioactivity, is disposed of in specially designed shallow burial sites with liners to prevent contamination of soil and groundwater.
• These sites are constantly monitored.

On-Site Storage

• Intermediate-level waste is typically stored on-site at nuclear facilities in shielded containers.
• Concrete casks or vaults are common storage solutions.

Geological Disposal

• This is a potential long-term solution for high-level waste disposal.
• The waste is encapsulated in special containers and buried deep underground in stable geological formations like granite or clay.
• But,
  • Studies have pointed to the risk of radioactive material becoming exposed to humans if the containers are disturbed, such as by nearby digging activity.

Vitrification

• For high-level waste storage, vitrification is a process where the waste is converted into a glass-like substance for improved stability and containment.

Reprocessing

• It is the technology that separate fissile from non-fissile material in spent fuel.
  • It presents the advantage of higher fuel efficiency.
• Some countries reprocess spent nuclear fuel to extract reusable fissile material like plutonium. (Like India)
• But,
  • Because spent fuel is so hazardous, the reprocessing process is complex, and expensive, and creates additional waste streams needing disposal.

Transmutation

• This theoretical approach involves using advanced reactors to convert long-lived radioactive isotopes in waste into shorter-lived or stable isotopes, reducing their radioactivity.
  • Transmutation technology is still under development.

What are the challenges of Nuclear Waste Management?

• Safe Storage: Finding a secure location for long-term (thousands of years) isolation.
  • Spent fuel rods remain radioactive for thousands of years, posing a long-term waste management challenge.
• Transportation & Storage Technologies: Safe methods to move and store waste are crucial.
  • Safe and secure storage of these rods is crucial to prevent radiation leaks and environmental contamination.
• Accident Risks: Contamination of water resources from leaks or accidents during storage/transport.
• Unknown unknowns: Uncertainties about long-term behavior of waste storage sites and reprocessing effectiveness.
• Ethical Concerns: Equity in waste storage (environmental justice) and burden sharing between generations.
• Cost factor: Waste management adds significantly to the cost of nuclear power generation.

What is the India's Scenario?

• According to a 2015 report from 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.
  • It produces 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).
  • The other, commissioned in 2011, has a capacity of 100 tHM/y.
• The third facility in Kalpakkam processes 100 tHM/y.
• India has adopted the Closed Fuel Cycle option.

• It involves reprocessing and recycling of the spent fuel.
• Reprocessing plants extract plutonium for further use (stage II reactors and potentially weapons).
  • During reprocessing, only about 2-3% of the spent fuel becomes waste.
  • This waste is called high level waste (HLW).
  • It is converted into glass through vitrification.
  • The vitrified waste is stored in a Solid Storage Surveillance Facility for 30-40 years beforethe its disposal.
  • The need for a final disposal facility will arise only after three to four decades.
• On-site storage facilities for low and intermediate waste with environmental monitoring.

Also, delays in the Fast Breeder Reactor (PFBR) program raise concerns about reprocessing plant efficiency. Why?

• According to the IPFM report
  • 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 – it will bring its own complications.
    • Because it will have a different distribution of fission products and transuranic elements.

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