Model Answer
0 min readIntroduction
Nuclear energy, while a low-carbon source of electricity, generates radioactive waste as a byproduct. Among these, high-level nuclear waste (HLW) poses the most significant long-term environmental and health risks due to its intense radioactivity and long half-lives. This waste primarily consists of spent nuclear fuel and reprocessing waste. Safe and permanent disposal of HLW is a global challenge, with geological repositories being the internationally favoured solution. This answer will detail the nature of HLW, its management strategies, the principles of geological disposal, and the current status in India.
What is High-Level Nuclear Waste?
High-Level Nuclear Waste (HLW) is radioactive waste that generates significant heat and contains high concentrations of fission products and minor actinides. It’s categorized based on its radioactivity and thermal output. Key characteristics include:
- Composition: Primarily spent nuclear fuel (SNF) from reactors, and waste from reprocessing SNF. SNF contains uranium, plutonium, and highly radioactive fission products.
- Radioactivity: Extremely high levels of radioactivity, requiring robust shielding.
- Half-life: Contains isotopes with half-lives ranging from hundreds to thousands of years, necessitating long-term isolation.
- Thermal Output: Generates substantial heat due to radioactive decay, requiring cooling during initial storage.
Management of High-Level Nuclear Waste
Managing HLW involves several stages, aiming to reduce its volume, heat, and radioactivity before final disposal:
- Interim Storage: Initially, SNF is stored in water-filled cooling pools at reactor sites for 5-10 years to allow for decay of short-lived isotopes and heat reduction.
- Dry Cask Storage: After cooling, SNF is transferred to dry storage casks – robust containers made of steel and concrete – for decades.
- Reprocessing (Optional): Some countries (e.g., France, Russia) reprocess SNF to extract usable plutonium and uranium, reducing the volume of HLW but creating additional waste streams.
- Vitrification: A process where HLW is mixed with molten glass and poured into stainless steel canisters. This creates a stable, solid waste form resistant to leaching.
Geological Disposal: The Preferred Solution
Geological disposal involves isolating HLW deep underground in stable geological formations. The concept relies on a multi-barrier system:
- Waste Form: Vitrified waste or SNF itself.
- Canister: Corrosion-resistant canisters (e.g., stainless steel, copper) encasing the waste.
- Buffer/Backfill: Materials (e.g., bentonite clay) surrounding the canisters to absorb water, retard radionuclide migration, and provide physical protection.
- Geological Formation: A stable geological environment with low permeability, minimal groundwater flow, and predictable long-term behaviour.
Site Selection Criteria
Choosing a suitable geological repository site is crucial. Key criteria include:
- Geological Stability: Absence of active faults, seismic activity, and volcanic activity.
- Hydrogeology: Low groundwater flow rate and minimal interaction with aquifers.
- Rock Properties: Low permeability, high sorption capacity (ability to bind radionuclides), and mechanical strength.
- Depth: Sufficient depth (typically 500-1000 meters) to provide isolation and shielding.
Examples of Geological Repositories
- Onkalo (Finland): Under construction in Olkiluoto, utilizing crystalline bedrock.
- Forsmark (Sweden): Planned repository in crystalline bedrock.
- Yucca Mountain (USA): Proposed repository in volcanic tuff (currently stalled due to political and social opposition).
Indian Scenario
India’s nuclear power program generates HLW primarily from its Pressurized Heavy Water Reactors (PHWRs). Currently, HLW is stored at reactor sites in interim storage facilities (cooling pools and dry storage). India does not currently reprocess all its spent fuel.
- HLW Management Facility (HWMF): A dedicated HWMF is under construction at Tarapur, Maharashtra, for interim storage and eventual processing of HLW.
- Geological Repository Project: The Department of Atomic Energy (DAE) is actively investigating potential sites for a geological repository. The focus is on identifying suitable geological formations, primarily crystalline rocks and granites.
- BARC’s Role: Bhabha Atomic Research Centre (BARC) is involved in research and development related to waste management, including vitrification and repository design.
The establishment of a geological repository in India faces challenges including site selection, public acceptance, and regulatory frameworks.
Conclusion
The safe and permanent disposal of high-level nuclear waste is a complex undertaking requiring robust engineering, geological understanding, and public trust. Geological repositories, employing a multi-barrier system, represent the internationally accepted solution. India is making progress towards establishing its own HLW management and disposal infrastructure, but faces challenges in site selection and public perception. Continued research, transparent communication, and a robust regulatory framework are essential for ensuring the long-term safety of nuclear waste disposal.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.