Nuclear Technology

Dual-Use Nature

• Nuclear technology has both civilian and military applications, making it controversial and sensitive.
• Civilian use: Electricity generation, medicine, research, agriculture.
• Military use: Nuclear weapons, submarines, and strategic deterrence.

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Reason Behind Energy Creation

• The atomic nucleus consists of protons and neutrons.
• During nuclear reactions, a small amount of mass is lost (mass defect), which is converted into enormous energy according to Einstein’s Theory of Relativity:

E=mc2E = mc^2E=mc2

where:

• E = Energy
• m = Mass lost (mass defect)
• c = Speed of light

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Fission Reaction

• In fission, the nucleus of a large atom (mass = M) splits into two smaller nuclei (m₁ + m₂).
• A mass deficit occurs: M>m1+m2M > m₁ + m₂M>m1​+m2​
• The difference (Δm = M – (m₁ + m₂)) is released as energy.
• Example: Splitting of Uranium-235 or Plutonium-239.

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Fusion Reaction

• In fusion, two lighter nuclei combine to form a heavier nucleus.
• Here, m1+m2>Mm₁ + m₂ > Mm1​+m2​>M
• The missing mass (Δm = (m₁ + m₂) – M) is again released as energy.
• Example: Fusion of Deuterium (²H) and Tritium (³H) to form Helium.

Nuclear Fission and Fusion

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Nuclear Fission

Definition:
The energetic splitting of a large, unstable nucleus into two relatively smaller nuclei, accompanied by the release of neutrons and a large amount of energy.

Reaction Example: 92235U+01n    →    54141Xe+3692Kr+3 01n+Energy{}^{235}_{92}\text{U} + {}^{1}_{0}\text{n} \;\; \rightarrow \;\; {}^{141}_{54}\text{Xe} + {}^{92}_{36}\text{Kr} + 3\,{}^{1}_{0}\text{n} + \text{Energy}92235​U+01​n→54141​Xe+3692​Kr+301​n+Energy

Key Points:

• Initiated when Uranium-235 absorbs a slow neutron.
• Releases ~200 MeV per fission reaction.
• Produces chain reactions (basis of nuclear reactors and atomic bombs).
• First harnessed during the Manhattan Project (WWII).

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Nuclear Fusion

Definition:
The process of joining two light nuclei to form a larger, stable nucleus, releasing enormous energy.

Reaction Example (Deuterium–Tritium Fusion): 12H+13H    →    24He+01n+Energy{}^{2}_{1}\text{H} + {}^{3}_{1}\text{H} \;\; \rightarrow \;\; {}^{4}_{2}\text{He} + {}^{1}_{0}\text{n} + \text{Energy}12​H+13​H→24​He+01​n+Energy

Why Fusion is Considered Superior to Fission:

1. Higher Energy Yield: Fusion releases much more energy per reaction than fission.
2. Abundant Fuel: Uses isotopes of hydrogen (Deuterium and Tritium), which can be derived from water and lithium, unlike Uranium/Thorium which are finite.
3. Cleaner By-products: Produces helium (an inert gas) and tritium (manageable), unlike fission which generates long-lived radioactive waste.
4. Safety: Fusion requires extreme conditions; if disturbed, the reaction stops immediately. No risk of uncontrolled chain reactions.
5. Non-Proliferative: Does not rely on fissile materials usable for nuclear weapons.

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Challenges in Achieving Nuclear Fusion

1. Requires extremely high temperatures (~150 million °C, similar to the Sun’s core).
2. Must maintain high plasma density to increase collision probability.
3. Plasma confinement is very difficult because it tends to expand. Solutions:
   • Magnetic confinement (Tokamaks, Stellarators).
   • Inertial confinement (high-power lasers).

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Fission vs Fusion: A Comparison

Aspect	Fission	Fusion
Definition	Splitting of a heavy nucleus into smaller nuclei	Combining of light nuclei into a heavier nucleus
Example Reaction	92235U+n→Xe+Kr+3n+Energy{}^{235}_{92}\text{U} + n \rightarrow Xe + Kr + 3n + \text{Energy}92235​U+n→Xe+Kr+3n+Energy	12H+13H→24He+n+Energy{}^{2}_{1}\text{H} + {}^{3}_{1}\text{H} \rightarrow {}^{4}_{2}\text{He} + n + \text{Energy}12​H+13​H→24​He+n+Energy
Fuel Used	Uranium-235, Plutonium-239, Thorium (U-233 in future)	Hydrogen isotopes (Deuterium, Tritium)
Energy Output	High (200 MeV per reaction)	Very high (≈ 17.6 MeV per D–T reaction; greater potential)
By-products	Long-lived radioactive waste	Helium (inert), minimal radioactive waste
Safety	Risk of uncontrolled chain reactions (Chernobyl, Fukushima)	Self-limiting; reaction stops if conditions not met
Proliferation	Can be weaponized into bombs	No direct weaponization risk
Technology	Mature; commercial use in nuclear reactors	Still experimental (ITER, EAST, NIF, etc.)

Nuclear Reactor

Definition

A nuclear reactor is a device that sustains and controls a chain reaction of nuclear fission. It is primarily used to generate electricity but also finds applications in:

• Propelling submarines and aircraft carriers,
• Producing medical and industrial isotopes,
• Conducting advanced nuclear research.

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Key Components

1. Core
   • The heart of the reactor, where fuel rods (zirconium-clad uranium or thorium) are placed.
   • Fission reactions in the core release heat.
   • Instrumentation and control systems are also embedded here.
2. Control Rods
   • Absorb excess neutrons to regulate the pace of the chain reaction.
   • Partially withdrawn → increases reaction rate; fully inserted → shuts down the reactor.
   • Materials: Boron, Silver, Cadmium, Indium.
3. Moderator
   • Slows down fast neutrons so that fission can occur efficiently.
   • Materials: Heavy water, graphite, beryllium.
   • Note: Fast Breeder Reactors do not need moderators.
4. Coolant
   • Circulates through the core to carry away heat and transfer it to turbines for power generation.
   • Common coolants: light water, heavy water, liquid sodium, helium.
5. Containment Unit
   • A thick concrete-and-steel shield surrounding the reactor.
   • Ensures radiation does not leak and accidents remain confined.

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Nuclear Fuels

• Uranium-235: Naturally fissile but only 0.7% of natural uranium. Needs enrichment.
• Uranium-238: Fertile; converts to fissile Plutonium-239 in breeder reactors.
• Thorium-232: Fertile; converts to fissile Uranium-233. Abundant in India.

Enrichment Levels:

• 3–5% U-235 → Power reactors (Light Water Reactors).
• ~20% U-235 → Research/breeder reactors.
• >90% U-235 → Nuclear weapons.

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Types of Reactors

1. Thermal Reactors

Use moderators to slow neutrons.

• Light Water Reactor (LWR):
  • Fuel: Enriched uranium.
  • Moderator & coolant: Light water.
• Pressurized Water Reactor (PWR):
  • Uses pressurized water as coolant.
  • Safer than BWR, as steam is generated in a separate loop.
• Pressurized Heavy Water Reactor (PHWR):
  • Uses natural uranium without enrichment.
  • Moderator & coolant: Heavy water.
  • Backbone of India’s nuclear power programme (220 MW, 540 MW, 700 MW units).
  Working Principle of PHWR:
  1. Fission heats heavy water in the primary loop.
  2. Heat is transferred to the secondary loop via a heat exchanger.
  3. Secondary loop water turns into steam → drives turbine → generates electricity.
  4. Closed loop ensures safety and efficiency.
• Boiling Water Reactor (BWR):
  • Simpler, cheaper design.
  • Water boils directly in the reactor vessel to produce steam.
  • Riskier as radioactive steam comes in direct contact with turbines.

Comparison: PHWR vs BWR

PHWR	BWR
Complex design	Simple design
Higher cost	Relatively economical
Higher electricity output	Lower output
Safer and more secure	Less safe

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2. Breeder Reactors

• Fast Breeder Reactor (FBR):
  • Generates more fissile material than it consumes.
  • No moderator used; relies on fast neutrons.
  • Coolant: Liquid sodium (does not slow neutrons).
  • Example: Prototype FBR at Kalpakkam (500 MW).
• Advanced Heavy Water Reactor (AHWR):
  • Coolant: Light water, Moderator: Heavy water.
  • Designed to exploit thorium fuel cycle (India’s Stage III).

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3. Emerging Designs

• Small Modular Reactors (SMRs):
  • Capacity: up to 300 MW.
  • Factory-assembled modules → lower cost, scalable, suitable for remote locations.
• Microreactors:
  • Capacity: up to 10 MW.
  • Portable, ideal for emergency use or powering isolated sites.

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Summary

India’s 3-Stage Nuclear Program

• Conceived by Homi J. Bhabha to optimally use India’s limited uranium (≈2% of global reserves) and vast thorium (≈25% of global reserves).
• India follows a closed fuel cycle (spent fuel is reprocessed) to maximise energy potential.

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Stage I: Pressurised Heavy Water Reactors (PHWRs)

• Fuel: Natural uranium (99.3% U-238, 0.7% U-235).
• U-235 undergoes fission → releases energy.
• U-238 absorbs neutrons → converts to Plutonium-239 (Pu-239) for Stage II.
• Closed-cycle reprocessing adopted: Pu-239 is separated from spent fuel.
  • Open cycle: entire waste disposed → energy underutilisation.
  • Closed cycle: Pu-239 & U-238 separated, recycled; only high-level waste vitrified and stored.

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Stage II: Fast Breeder Reactors (FBRs)

• Fuel: Pu-239 + U-238.
• Reactor produces more Pu-239 than it consumes.
• Once adequate plutonium is available, thorium (Th-232) replaces U-238.
• Th-232 → converted to U-233 (fissile).

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Stage III: Advanced Heavy Water Reactors (AHWRs)

• Fuel: U-233 bred from thorium.
• Th-232 continually converted to more U-233, creating a self-sustaining thorium cycle.
• Objective: Long-term, sustainable, thorium-based energy independence.

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India’s Nuclear Reactors (Operational & Planned)

Location	Reactor Type	Units	Under Construction
Tarapur, Maharashtra	2 PHWR, 2 BWR, 2 PWR	6	–
Kudankulam, Tamil Nadu	2 VVER (Russian)	2	+2
Kaiga, Karnataka	PHWR	4	–
Rawat Bhata, Rajasthan	PHWR	2	–
Kalpakkam, Tamil Nadu	PHWR + Prototype FBR	2 (+1)	1 PFBR (500 MW)
Narora, Uttar Pradesh	PHWR	2	–
Gorakhpur, Haryana	PHWR	2	–
Chutka, Madhya Pradesh	PHWR	2	–
Mahi Banswara, Rajasthan	PHWR	4	–
New PHWR Sites	–	–	10 sanctioned

Site selection criteria:

1. Proximity to power-demand centres (e.g., Narora near NCR).
2. Avoidance of border/vulnerable areas.
3. Safety from seismic/flood risks.

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Nuclear Fusion

Tokamak (Magnetic Confinement Device)

• Fusion fuel: Deuterium + Tritium (D-T).
• Plasma heated → ions fuse → enormous energy.
• Heat absorbed by reactor walls → converted to steam → turbines → electricity.

Why D-T reaction?

• Gives highest energy output at relatively lower temperature compared to other fuels.

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Plasma Physics

• Plasma = ionised gas + free electrons.
• 99% of visible universe is plasma.
• Strongly responds to electromagnetic fields.

Energy input required:

• Thermal heating,
• Electrical currents,
• Laser or UV light.

Fusion in Tokamak:

1. Hydrogen gas → heated to millions °C → forms plasma.
2. Plasma confined by magnetic coils (10–100× Earth’s field).
3. If plasma touches chamber walls → heat lost → reaction extinguished.

Lawson Criterion (Triple Product): Plasma Density × Confinement Time × Temperature  ≥  Threshold\text{Plasma Density × Confinement Time × Temperature} \; \geq \; ThresholdPlasma Density × Confinement Time × Temperature≥Threshold

Threshold depends on type of fusion fuel.

Tritium Breeding:

• Produced from lithium: ^6Li + ^2_4He \; \rightarrow \; ^3T + ^1H

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ITER (International Thermonuclear Experimental Reactor)

• World’s largest fusion experiment, located at Cadarache, France.
• Launched: 1985, India joined in 2005.
• Members: USA, Russia, EU, China, Japan, S. Korea, India (35 nations total).
• First device aiming to produce net energy from fusion.

Objectives:

1. Achieve Q ≥ 10 (output ≥ 10× input).
2. Demonstrate integrated systems (plasma control, cryogenics, remote maintenance).
3. Sustain D-T plasma through internal heating.
4. Prove tritium breeding feasibility.
5. Demonstrate safety of fusion devices.

Cost Sharing (2006 Agreement):

• EU: 45.6%; Others: 9.1% each.

India’s Contribution:

• Cryogenic system,
• In-wall shielding,
• Cooling-water system,
• Ion cyclotron heating system,
• Diagnostic neutral-beam system,
• Power supplies.

Cryostat:

• Built by L&T.
• World’s largest stainless-steel vacuum-pressure chamber.
• Maintains ultra-cool environment for superconducting magnets.

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Safety in Nuclear Reactors

Medicine and Radioisotope Applications

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1. Diagnostic Applications

• Technetium-99 (Tc-99): Used in Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT).
  • Provides detailed imaging of both bone and soft tissues, superior to X-rays.
• Iodine-131 (as sodium iodide): Widely used in thyroid diagnosis and therapy.
• Radioisotopes in organ studies: Tracing blood flow to specific organs for functional analysis.
• F-18 Fluoro Deoxy Glucose (FDG): Detects tissues with high glucose uptake (e.g., cancer cells, brain activity).

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2. Therapeutic Applications

• External beam radiation therapy:
  • Cobalt-60 gamma radiation for cancer treatment.
• Brachytherapy (short-range radiotherapy):
  • Iridium-192, Caesium-137, Iodine-125, Palladium-102 used for localised tumour treatment.
• Bone pain palliation:
  • Phosphorus-32, Samarium-153 used for bone metastasis.
• Sterilisation using radiation (Co-60 gamma rays):
  • Safer and cheaper than steam heating.
  • Suitable for heat-sensitive medical instruments and biological preparations.
  • Extends shelf life of medical products.

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3. Food Irradiation

• Process: Food is exposed to gamma rays, high-energy electrons, or X-rays.
• Mechanism: Radiation damages DNA of microorganisms → prevents reproduction.
• Benefits:
  1. Extends shelf life without affecting nutritional value.
  2. Cost-effective compared to chemicals.
  3. Leaves no chemical residue; suitable for trade.
  4. Can be irradiated after packaging.
  5. Reduces food spoilage & risk of foodborne diseases.
  6. Less need for preservatives/additives.
  7. Replaces harmful fumigants.
  8. Safe: does not make food radioactive.
  9. Used for astronaut food preservation.

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4. Radioisotopes in Agriculture and Industry

• Crop improvement: Irradiation of seeds (Co-60) → mutagenic breeding → new crop varieties.
• Fertiliser studies:
  • N-15, P-32 isotopes used to trace uptake, fixation, and losses.
  • Helps optimise fertiliser usage.
• Environmental tracers: Used in pollutant tracking.
• Industrial tracers:
  • Monitor flow rates & mixing.
  • Locate leaks in pipelines.
  • Measure engine wear & tear using isotopes in lubricants.
  • Improve equipment performance.

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5. Space and Desalination

• Radioisotope power sources (RTGs): Used in satellites, deep-space missions, pacemakers.
  • Example: Curium-238 and Plutonium-238 RTGs powered Voyager 1 (1977– ), Cassini, Curiosity Rover.
• Nuclear energy in desalination: Provides reliable heat and energy for large-scale water desalination projects.

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6. Other Applications

• Radiocarbon dating (C-14): Estimation of age of fossils, rocks, archaeological artefacts.
• Americium-241: Used in household smoke detectors.
• Sterile Insect Technique: Insect eggs irradiated → sterilises males → no progeny with wild females → population control.

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Relevance of Nuclear Energy

1. Energy efficiency: Fusion releases millions of times more energy per unit mass than coal.
2. Energy security: India’s growing energy demand + dependence on fossil imports → vulnerability.
3. Environmental savings: Reduces health, climate, and pollution-related costs.
4. Limitations of renewables:
   • Land-intensive (solar/wind farms).
   • Intermittent power (day-night, seasonal).
   • Reliance on imported technology & materials.
   • Storage challenges.
5. Reliability: Nuclear power plants have high load factor (80–90%).
6. Fuel efficiency: Very small amount of fuel needed → low transport and storage costs.

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Challenges in Harnessing Nuclear Energy

1. High capital cost for setting up reactors.
2. Restricted access to nuclear technology and uranium.
3. Limited skilled manpower for plant design & operation.
4. Safety risks (meltdowns, radiation leaks).
5. Nuclear waste management (long half-life isotopes).

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Nuclear Accidents (To be detailed)

Department of Atomic Energy (DAE)

• Established: 1954, under the direct charge of the Prime Minister.
• Legal Basis: Operates under the Atomic Energy Act, 1948.
• Mandate: Implements India’s atomic energy policy and oversees research, development, and application of nuclear science and technology.

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Atomic Energy Commission (AEC)

• First set up: 1948.
• Reconstituted under DAE: 1958.
• Role: Apex body responsible for policy formulation, strategic decisions, and overall guidance of the DAE.

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DAE Organisational Structure

• Research Centres: 6
• Industrial Organisations: 3
• Public Sector Undertakings (PSUs): 5
• Grant-in-Aid Institutes: 11
• Boards: 2 → NBHM (National Board for Higher Mathematics) & BRNS (Board of Research in Nuclear Sciences)

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Research Centres

1. Bhabha Atomic Research Centre (BARC), Mumbai (1954)
   • Originally Atomic Energy Establishment, Trombay. Renamed in 1966 after Homi Bhabha.
   • India’s premier nuclear research hub (reactor design, isotope applications, waste management).
2. Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam (1971)
   • Specialises in sodium-cooled Fast Breeder Reactors.
   • KAMINI Reactor (1996): World’s only reactor operating on U-233 fuel.
3. Raja Ramanna Centre for Advanced Technology (RRCAT), Indore (1984)
   • Focus: lasers, particle accelerators, advanced technologies.
4. Variable Energy Cyclotron Centre (VECC), Kolkata (1977)
   • Specialises in nuclear physics research.
   • Collaborates with CERN (European Organisation for Nuclear Research).
5. Atomic Minerals Directorate for Exploration and Research (AMD), Hyderabad (1948)
   • Responsible for exploration of uranium, thorium, and rare earth deposits.
6. Global Centre for Nuclear Energy Partnership (GCNEP), Khandwa, Madhya Pradesh
   • Aims to promote global cooperation in nuclear energy and safety.

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Industrial Organisations

1. Nuclear Fuel Complex (NFC), Hyderabad
   • Supplies fuel assemblies to India’s nuclear power plants.
   • Houses zirconium plants and uranium dioxide production facilities.
2. Heavy Water Board (HWB), Mumbai
   • Produces heavy water, enriched boron, nuclear-grade sodium and solvents.
   • India is among the world’s largest heavy-water producers and exporters.
3. Board of Radiation and Isotope Technology (BRIT), Mumbai
   • Supplies radioisotopes and radiation technology for medical, agricultural, and industrial use.

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Public Sector Undertakings (PSUs)

1. Nuclear Power Corporation of India Limited (NPCIL), Mumbai (1987)
   • Designs, constructs, commissions, and operates nuclear power plants.
2. Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), Kalpakkam (2003)
   • Constructs the 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, based on IGCAR design.
3. Electronics Corporation of India Limited (ECIL), Hyderabad (1967)
   • Provides electronics for defence, nuclear, and space sectors.
4. Uranium Corporation of India Limited (UCIL), Jaduguda (1967)
   • Engaged in uranium mining and processing.
5. Indian Rare Earths Limited (IREL), Mumbai
   • Processes beach sand minerals for thorium and other rare earths.

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Nuclear Regulations

Atomic Energy Regulatory Board (AERB)

• Constituted: 1983 by President of India under Atomic Energy Act, 1962.
• Legal Powers: Drawn from Environment Protection Act, 1986 and Factories Act, 1948.
• Mission: Ensure nuclear and radiation safety → protect workers, public, and environment.
• Composition: Maximum of 6 members.
  • Includes 2 whole-time members (Chairperson + another).
  • Executive Director (ex-officio) as whole-time member.
  • Assisted by a non-member Secretary.
• Accountability: Reports to Atomic Energy Commission (AEC).