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  • 22 August, 2021

  • 25 Min Read

Nuclear Fusion Energy

What is Nuclear Fusion?

  • Fusion is the energy source of the Sun and stars. In the tremendous heat and gravity at the core of these stellar bodies, hydrogen nuclei collide, fuse into heavier helium atoms and release tremendous amounts of energy in the process.
  • Nuclear fusion is defined as the combining of several small nuclei into one large nucleus with the subsequent release of huge amounts of energy. Nuclear fusion powers our sun and harnessing this fusion energy could provide an unlimited amount of renewable energy.
  • Twentieth-century fusion science identified the most efficient fusion reaction in the laboratory setting to be the reaction between two hydrogen isotopes, deuterium (D) and tritium (T).
  • The DT fusion reaction produces the highest energy gain at the "lowest" temperatures.
  • Three conditions must be fulfilled to achieve fusion in a laboratory:
    1. Very high temperature (on the order of 150,000,000° Celsius);
    2. Sufficient plasma particle density (to increase the likelihood that collisions do occur); and
    3. Sufficient confinement time (to hold the plasma, which has a propensity to expand, within a defined volume).
  • At extreme temperatures, electrons are separated from nuclei and a gas becomes a plasma—often referred to as the fourth state of matter. Fusion plasmas provide the environment in which light elements can fuse and yield energy.
  • In a tokamak device, powerful magnetic fields are used to confine and control the plasma.

So how exactly does nuclear fusion work?

  • Simply put, nuclear fusion is the process by which two light atomic nuclei combine to form a single heavier one while releasing massive amounts of energy.
  • Fusion reactions take place in a state of matter called plasmaa hot, charged gas made of positive ions and free-moving electrons that has unique properties distinct from solids, liquids and gases.
  • To fuse on our sun, nuclei need to collide with each other at very high temperatures, exceeding ten million degrees Celsius, to enable them to overcome their mutual electrical repulsion.
  • Once the nuclei overcome this repulsion and come within a very close range of each other, the attractive nuclear force between them will outweigh the electrical repulsion and allow them to fuse.
  • For this to happen, the nuclei must be confined within a small space to increase the chances of collision.
  • In the sun, the extreme pressure produced by its immense gravity create the conditions for fusion to happen.
  • The amount of energy produced from fusion is very large — four times as much as nuclear fission reactions — and fusion reactions can be the basis of future fusion power reactors.
  • Plans call for first-generation fusion reactors to use a mixture of deuterium and tritium — heavy types of hydrogen.
  • In theory, with just a few grams of these reactants, it is possible to produce a terajoule of energy, which is approximately the energy one person in a developed country needs over sixty years.
  • While the sun’s massive gravitational force naturally induces fusion, without that force a higher temperature is needed for the reaction to take place.
  • On earth, we need temperatures exceeding 100 million degrees Celsius and intense pressure to make deuterium and tritium fuse, and sufficient confinement to hold the plasma and maintain the fusion reaction long enough for a net power gain, i.e. the ratio of the fusion power produced to the power used to heat the plasma.
  • Nuclear fusion and plasma physics research are carried out in more than 50 countries, and fusion reactions have been successfully achieved in many experiments, albeit without demonstrating a net fusion power gain.

Historical Background for collaborations

  • Ever since nuclear fusion was understood in the 1930s, scientists have been on a quest to recreate and harness it. Initially, these attempts were kept secret. However, it soon became clear that this complex and costly research could only be achieved through collaboration.
  • At the second United Nations International Conference on the Peaceful Uses of Atomic Energy, held in 1958 in Geneva, Switzerland, scientists unveiled nuclear fusion research to the world.

Role of International Atomic Energy Agency (IAEA)

  • The IAEA has been at the core of international fusion research. The IAEA launched the Nuclear Fusion journal in 1960 to exchange information about advances in nuclear fusion, and it is now considered the leading periodical in the field.
  • The first international IAEA Fusion Energy Conference was held in 1961 and, since 1974, the IAEA convenes a conference every two years to foster discussion on developments and achievements in the field.

International Thermonuclear Experimental Reactor (ITER)

  • After two decades of negotiations on the design and location of the world’s largest international fusion facility, ITER was established in 2007 in France, with the aim of demonstrating the scientific and technological feasibility of fusion energy production.
  • In southern France, 35 nations* are collaborating to build the world's largest tokamak, a magnetic fusion device that has been designed to prove the feasibility of fusion as a large-scale and carbon-free source of energy based on the same principle that powers our Sun and stars.
  • ITER will be the first fusion device to produce net energy. ITER will be the first fusion device to maintain fusion for long periods of time.
  • And ITER will be the first fusion device to test the integrated technologies, materials, and physics regimes necessary for the commercial production of fusion-based electricity.
  • Thousands of engineers and scientists have contributed to the design of ITER since the idea for an international joint experiment in fusion was first launched in 1985.
  • The ITER Members—China, the European Union, India, Japan, Korea, Russia and the United States—are now engaged in a 35-year collaboration to build and operate the ITER experimental device, and together bring fusion to the point where a demonstration fusion reactor can be designed.

  • What will ITER do?
    1. Produce 500 MW of fusion power
    2. Demonstrate the integrated operation of technologies for a fusion power plant
    3. Achieve a deuterium-tritium plasma in which the reaction is sustained through internal heating
    4. Test tritium breeding
    5. Demonstrate the safety characteristics of a fusion device.
  • ITER's First Plasma is scheduled for December 2025. That will be the first time the machine is powered on, and the first act of ITER's multi-decade operational program.

What is a Tokamak?

  • Power plants today rely either on fossil fuels, nuclear fission, or renewable sources like wind or water.
  • Whatever the energy source, the plants generate electricity by converting mechanical power, such as the rotation of a turbine, into electrical power.
  • In a coal-fired steam station, the combustion of coal turns water into steam and the steam in turn drives turbine generators to produce electricity.
  • The tokamak is an experimental machine designed to harness the energy of fusion.
  • Inside a tokamak, the energy produced through the fusion of atoms is absorbed as heat in the walls of the vessel.
  • Just like a conventional power plant, a fusion power plant will use this heat to produce steam and then electricity by way of turbines and generators.
  • The heart of a tokamak is its doughnut-shaped vacuum chamber.
  • Inside, under the influence of extreme heat and pressure, gaseous hydrogen fuel becomes a plasma—the very environment in which hydrogen atoms can be brought to fuse and yield energy.
  • The charged particles of the plasma can be shaped and controlled by the massive magnetic coils placed around the vessel; physicists use this important property to confine the hot plasma away from the vessel walls.
  • The term "tokamak" comes to us from a Russian acronym that stands for "toroidal chamber with magnetic coils."
  • First developed by Soviet research in the late 1960s, the tokamak has been adopted around the world as the most promising configuration of magnetic fusion device.
  • ITER will be the world's largest tokamak—twice the size of the largest machine currently in operation, with ten times the plasma chamber volume.

What are the effects of fusion on the environment?

  • Fusion is among the most environmentally friendly sources of energy.
  • There are no CO2 or other harmful atmospheric emissions from the fusion process, which means that fusion does not contribute to greenhouse gas emissions or global warming.
  • Its two sources of fuel, hydrogen and lithium, are widely available in many parts of the Earth.
  • Nuclear fusion is a clean and green route to producing energy, as it does not involve any remnant radioactive waste products. Fusion reactions power hydrogen bombs. However, so far, fusion devices that show a net energy gain have not been demonstrated in labs.

What’s the difference between nuclear fission and nuclear fusion?

  • Both are nuclear processes, in that they involve nuclear forces to change the nucleus of atoms.
  • Chemical processes on the other hand involve mainly electromagnetic force to change only the electronic structure of atoms.
  • Fission splits a heavy element (with a high atomic mass number) into fragments; while fusion joins two light elements (with a low atomic mass number), forming a heavier element.
  • In both cases, energy is freed because the mass of the remaining nucleus is smaller than the mass of the reacting nuclei.
  • The reason why opposite processes release energy can be understood by examining the binding energy per nucleon curve. Both fusion and fission reactions shift the size of the reactant nuclei towards higher bounded nuclei.

Does Fusion produce radioactive nuclear waste the same way fission does?

  • Nuclear fission power plants have the disadvantage of generating unstable nuclei; some of these are radioactive for millions of years.
  • Fusion on the other hand does not create any long-lived radioactive nuclear waste.
  • A fusion reactor produces helium, which is an inert gas.
  • It also produces and consumes tritium within the plant in a closed circuit. Tritium is radioactive (a beta emitter) but its half life is short. It is only used in low amounts so, unlike long-lived radioactive nuclei, it cannot produce any serious danger.
  • The activation of the reactor’s structural material by intense neutron fluxes is another issue.
  • This strongly depends on what solution for blanket and other structures has been adopted, and its reduction is an important challenge for future fusion experiments.

Can fusion cause a nuclear accident?

  • No, because fusion energy production is not based on a chain reaction, as is fission.
  • Plasma must be kept at very high temperatures with the support of external heating systems and confined by an external magnetic field.
  • Every shift or change of the working configuration in the reactor causes the cooling of plasma or the loss of its containment; in such a case, the reactor would automatically come to a halt within a few seconds, since the process of energy production is arrested, with no effects taking place on the outside.
  • For this reason fusion reactors are considered to be inherently safe.

Can fusion reactors be used to produce weapons?

  • No. Although hydrogen bombs do use fusion reactions, they require an additional fission bomb to detonate.
  • Working conditions of a magnetically-confined fusion reactor require a limited amount of fuel in the reactor.
  • This fuel is continuously injected and consumed; therefore there is never a sufficient amount of fuel to produce the instantaneous power required for a weapon.

Why in news? U.S. lab makes headway in nuclear fusion energy

  • An experiment at the U.S. National Ignition Facility (NIF), within the Lawrence Livermore National Laboratory, Livermore, California, comes close to demonstrating this. In this lab, using laser beams, tiny pellets of deuterium and tritium (heavier isotopes of hydrogen) have been fused to form helium and release energy that very nearly matches the amount of energy input using the lasers.
  • The NIF has been trying to achieve this for nearly a decade. Now, the experiment has produced a yield that almost equals the laser energy input. To be functional, a reactor has to produce an output that is at least tens of times the input energy.
  • A tiny pellet of the fuel (deuterium and tritium) is placed in a cylidrical thumbnail-sized vessel, known as a hohlraum that has holes on both faces. A total of 192 laser beams are directed through the holes to strike the walls of the hohlraum. This causes the hohlraum to emit x-rays which, in turn, impinge on the pellet and compress it. The heated core of the pellet reaches 100 million degrees temperature which starts the fusion reactions. Further, the pellet has to “ignite” and only then can it reach the stage of becoming a microbomb – a deuterium-tritium fusion reactor – and release energy that can be tapped.

Laser facility

  • The laser facility itself occupies a large area, equal to nearly three cricket fields, and the lasers can deliver up to 500 terawatts of power using its 192 individual laser beams. This is focused into the openings in the hohlraum which contains the pellet measuring some 2-3 mm.
  • “The amount of laser energy used in these experiments is quite modest, 1.9 megajoule (MJ). This is approximately equal to the energy it takes to heat a large pot (8 litres) of water by 100 degrees Celsius. The amount of fusion energy produced in these experiments was approximately 1.3 MJ which is now for the first time comparable to amount of laser energy input.
  • This is the first time, in a controlled laboratory setting, that an inertial fusion system (another name for a laser driven fusion system) has produced nearly as much energy was supplied to initiate the reaction.
  • If we do the energy accounting we estimate that the fusion energy production is approximately 5 times the amount of energy coupled from the laser to target.

Tremendous progress

  • To make a fusion reactor, hundreds of pellet implosions have to happen per second and means have to be found to extract the neutron energy as heat and produce electricity. This [experiment] is far from that stage, but the researchers have made tremendous progress in the last decade.
  • Several steps remain before a viable nuclear fusion reactor can be realised. Ignition, or energy break-even must be achieved.
  • Many laser pulses must be made to act per second to increase the net yield to a sufficiently high value. Then the technology to convert the neutron energy into electricity has to be developed.
  • The fusion energy produced is released in an incredibly short amount of time, approximately, 90 picoseconds producing close to 15 petawatts of power. This is approximately equivalent to some recent estimates of the total world power consumption, however the experiment only produces this power for an incredibly short period of time, whereas power is consumed continuously across the world.”

How was the new breakthrough achieved?

  • The team used new diagnostics, improved laser precision, and even made changes to the design. They applied laser energy on fuel pellets to heat and pressurise them at conditions similar to that at the centre of our Sun. This triggered the fusion reactions.
  • These reactions released positively charged particles called alpha particles, which in turn heated the surrounding plasma. (At high temperatures, electrons are ripped from atom’s nuclei and become a plasma or an ionised state of matter. Plasma is also known as the fourth state of matter)
  • The heated plasma also released alpha particles and a self-sustaining reaction called ignition took place. Ignition helps amplify the energy output from the nuclear fusion reaction and this could help provide clean energy for the future.
  • On August 8, the team noted an energy output of more than 1.3 megajoules. The findings are yet to be published in a peer-reviewed journal.

UK hatches plan to build world's first fusion power plant

  • In June, JET will begin fusing even quantities of tritium and deuterium, another isotope of hydrogen. It is this fuel mix that ITER will use in its attempt to create more power from a fusion reaction than is put in — something that has never before been demonstrated. The reactor should heat and confine a plasma of deuterium and tritium such that the fusion of the isotopes into helium produces enough heat to sustain further fusion reactions.

Institute of Plasma Research, India

  • The Institute for Plasma Research (IPR) was established in 1986 as an autonomous R&D institute under the Department of Science and Technology (DST) with a mandate to pursue research in plasma science and technology. The institute grew rapidly and came under the administrative umbrella of the Department of Atomic Energy (DAE) in 1995.
  • This institute is largely involved in theoretical and experimental studies in plasma science including basic plasma physics, magnetically confined hot plasmas and plasma technologies for industrial application.
  • The institute owns two operational tokamaks (a machine for controlling thermonuclear fusion) - ADITYA and Steady State Tokamak (SST)-1.
  • FCIPT, ITER-India and CPP-IPR, located in Gandhinagar and Guwahati are three divisions under IPR.

Aditya Tokamac in India

  • ADITYA is the first indigenously designed and built tokamak of the country. It was commissioned in 1989.
  • ADITYA, a medium size Tokamak, is being operated for over a decade. It has a major radius of 0.75m and minor radius of the plasma is 0.25 m.
  • A maximum of 1.2 T toroidal magnetic field is generated with the help of 20 toroidal field coils spaced symmetrically in the toroidal direction. The major subsystems and parameters of the machine have been described elsewhere.
  • ADITYA is regularly being operated with the transformer-converter power system. ~100 msec 80 - 100 kA plasma discharges at toroidal field of 8.0 kG are being regularly studied.
  • During this period experiments on edge plasma fluctuations, turbulence and other related works have been conducted. Standard diagnostics have been employed during these measurements.

Steady State Superconducting Tokamac

  • A steady state superconducting tokamak SST-1 is under design and fabrication at the Institute for Plasma Research.
  • The objectives of SST-1 include studying the physics of the plasma processes in tokamak under steady state conditions and learning technologies related to the steady state operation of the tokamak.
  • These studies are expected to contribute to the tokamak physics database for very long pulse operations.
  • The SST-1 tokamak is a large aspect ratio tokamak, configured to run double null diverted plasmas with significant elongation (k) and triangularity (d).
  • The specific objective of the SST-1 project is to produce 1000 s elongated double null divertor plasma.There are several conventional questions in tokamak physics, which will be addressed again in steady state scenario.
  • Some of these are related to the energy, particle and impurity confinement, the effect of impurities and edge localized modes (ELM) in steady on energy confinement, the stability limits and their dependence on current drive methods, the resistive tearing activities in presence of RF fields, disruptions and vertical displacement events (VDE), and thermal instability.

Way Forward

  • It is expected that fusion could meet humanity’s energy needs for millions of years. Fusion fuel is plentiful and easily accessible: deuterium can be extracted inexpensively from seawater, and tritium can be produced from naturally abundant lithium.
  • Future fusion reactors will not produce high activity, long lived nuclear waste, and a meltdown at a fusion reactor is practically impossible.
  • Importantly, nuclear fusion does not emit carbon dioxide or other greenhouse gases into the atmosphere, and so along with nuclear fission could play a future climate change mitigating role as a low carbon energy source.

Source: TH

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