☢️Nuclear Fusion Technology Unit 1 – Introduction to Nuclear Fusion

What's Nuclear Fusion?

• Fundamental process that powers the stars and the sun
• Occurs when light atomic nuclei combine to form heavier nuclei, releasing large amounts of energy in the process
• Requires extremely high temperatures and pressures to overcome the electrostatic repulsion between positively charged nuclei
• Most common fusion reaction involves the isotopes of hydrogen: deuterium and tritium
  • Deuterium contains one proton and one neutron
  • Tritium contains one proton and two neutrons
• Fusion of deuterium and tritium produces helium-4, a neutron, and releases 17.6 MeV of energy
• Considered a potentially clean and virtually limitless source of energy for the future
• Differs from nuclear fission, which involves splitting heavy atomic nuclei to release energy

The Science Behind Fusion

• Fusion reactions occur in a state of matter called plasma, where electrons are separated from atomic nuclei
• Plasma is created by heating the fusion fuel to extremely high temperatures, typically over 100 million degrees Celsius
• At these temperatures, atoms collide with sufficient energy to overcome the Coulomb barrier and fuse together
• Fusion reactions are governed by the strong nuclear force, which is the force that binds protons and neutrons together in the atomic nucleus
• The energy released in fusion reactions is a result of the conversion of mass to energy, as described by Einstein's famous equation: $E=mc^2$
• Fusion reactions are highly sensitive to temperature, density, and confinement time of the plasma
  • These three factors are related by the Lawson criterion, which defines the conditions necessary for a self-sustaining fusion reaction
• Two main approaches to achieving fusion: magnetic confinement and inertial confinement
  • Magnetic confinement uses powerful magnetic fields to confine the plasma and keep it away from the reactor walls
  • Inertial confinement uses high-powered lasers or particle beams to compress and heat the fuel to fusion conditions

Fusion vs. Fission: What's the Difference?

• Fusion and fission are two different nuclear processes that release energy
• Fission involves splitting heavy atomic nuclei (uranium or plutonium) into lighter elements, releasing energy and neutrons
• Fusion combines light atomic nuclei (hydrogen isotopes) to form heavier elements, releasing large amounts of energy
• Fission is the process used in current nuclear power plants, while fusion is still in the experimental and developmental stages
• Fusion has several potential advantages over fission:
  • Fusion fuel (deuterium and tritium) is abundant and widely distributed, while fission fuel (uranium) is limited and geographically concentrated
  • Fusion reactions produce no long-lived radioactive waste, while fission generates high-level radioactive waste that requires long-term storage
  • Fusion reactors have inherent safety features and are not prone to meltdowns or nuclear chain reactions, unlike fission reactors
• However, achieving sustained and economically viable fusion reactions has proven to be a significant scientific and engineering challenge

Key Players in Fusion Research

• International Thermonuclear Experimental Reactor (ITER): a multinational collaborative project to build the world's largest tokamak fusion reactor in France
  • Aims to demonstrate the scientific and technological feasibility of fusion power
  • Involves 35 countries, including the European Union, United States, China, India, Japan, Russia, and South Korea
• National Ignition Facility (NIF): a large laser-based inertial confinement fusion research facility at Lawrence Livermore National Laboratory in the United States
  • Focuses on achieving fusion ignition and gain using high-powered lasers
• Wendelstein 7-X: an advanced stellarator fusion device in Germany, designed to test the suitability of the stellarator concept for fusion power plants
• Joint European Torus (JET): the largest operational tokamak in the world, located in the United Kingdom
  • Holds the record for the highest energy output from a fusion reactor (59 megajoules)
• Several private companies, such as Commonwealth Fusion Systems, General Fusion, and TAE Technologies, are also working on developing fusion technology

Fusion Reactor Designs

• Tokamak: the most well-developed and widely studied fusion reactor design
  • Uses a toroidal (doughnut-shaped) magnetic field to confine the plasma
  • Plasma current is induced by transformer action and helps to stabilize the plasma
  • Examples include ITER, JET, and the Spherical Tokamak for Energy Production (STEP) proposed by the UK
• Stellarator: an alternative magnetic confinement design that uses complex twisted magnetic coils to confine the plasma
  • Does not require a plasma current, potentially making it more stable and easier to operate than tokamaks
  • Examples include Wendelstein 7-X and the Large Helical Device (LHD) in Japan
• Inertial Confinement Fusion (ICF): uses high-powered lasers or particle beams to compress and heat a small pellet of fusion fuel
  • Aims to achieve fusion ignition and gain in a single short pulse
  • Examples include the National Ignition Facility (NIF) and the Laser Megajoule (LMJ) in France
• Magnetized Target Fusion: a hybrid approach that combines elements of magnetic confinement and inertial confinement
  • Uses a magnetized plasma target that is compressed by an imploding liner or liquid metal
  • Being developed by companies such as General Fusion and Helion Energy

Challenges in Achieving Fusion

• Achieving and maintaining the extremely high temperatures (>100 million °C) required for fusion reactions
  • Plasma must be heated using methods such as ohmic heating, neutral beam injection, and radio-frequency waves
• Confining the hot plasma for a sufficient time to allow fusion reactions to occur
  • Plasma tends to be unstable and can escape confinement due to various instabilities and turbulence
• Ensuring the plasma is dense enough to achieve a high fusion reaction rate
  • Plasma density is limited by the strength of the magnetic fields that can be generated
• Developing materials that can withstand the intense heat and neutron bombardment in a fusion reactor
  • Plasma-facing components and structural materials must be resistant to erosion, radiation damage, and activation
• Efficiently breeding and extracting tritium fuel from the reactor
  • Tritium is rare and must be produced within the reactor by bombarding lithium with neutrons from the fusion reactions
• Designing efficient heat extraction and power generation systems to convert fusion energy into electricity
• Scaling up fusion reactors to commercially viable sizes while maintaining performance and efficiency

Potential Applications and Benefits

• Electricity generation: fusion power plants could provide a virtually limitless, clean, and safe source of electricity
  • Fusion fuel (deuterium) is abundant in seawater, and the Earth's supply could last for millions of years
  • Fusion reactions produce no greenhouse gases or long-lived radioactive waste
• Hydrogen production: fusion reactors could be used to generate high-temperature heat for thermochemical water splitting, producing hydrogen for use as a clean fuel
• Desalination: the heat from fusion reactors could be used to desalinate seawater, providing a source of fresh water for drinking and irrigation
• Space propulsion: fusion-powered spacecraft could enable faster and more efficient interplanetary travel
  • Fusion reactions produce high-speed particles that could be used for propulsion
  • Fusion fuel has a high energy density, allowing for longer missions with less fuel mass
• Medical isotope production: fusion reactors could be used to produce medical isotopes for diagnostic imaging and cancer treatment
  • Examples include technetium-99m for SPECT scans and actinium-225 for targeted alpha therapy
• Transmutation of nuclear waste: fusion neutrons could potentially be used to transmute long-lived radioactive waste from fission reactors into shorter-lived or stable isotopes

Future of Fusion Technology

• Continued research and development to overcome the scientific and engineering challenges in achieving fusion
  • Advances in plasma physics, materials science, and reactor design are needed
• Construction and operation of large-scale experimental fusion reactors, such as ITER, to demonstrate the feasibility of fusion power
  • ITER aims to produce 500 MW of fusion power for pulses of 400 seconds by the late 2030s
• Development of demonstration fusion power plants (DEMO) to showcase the commercial viability of fusion
  • DEMO reactors will aim to generate electricity and operate with a closed tritium fuel cycle
• Scaling up fusion reactor designs to commercial power plant sizes
  • Fusion power plants are expected to have a capacity of 1-2 GW, similar to large fission reactors
• Reducing the cost and improving the efficiency of fusion reactor components and systems
  • Advances in superconducting magnets, plasma heating systems, and tritium breeding technology are needed
• Increasing private sector investment and involvement in fusion research and development
  • Several startup companies are pursuing alternative fusion reactor designs and technologies
• Establishing a regulatory framework and licensing process for fusion power plants
  • Fusion reactors will require unique safety and performance standards compared to fission reactors
• Developing a supply chain and workforce for the fusion industry
  • Specialized skills in plasma physics, cryogenics, and nuclear engineering will be needed