“Artificial sun” nuclear fusion reactor

Context: China successfully powered up its “artificial sun” nuclear fusion reactor for the first time, state media reported, marking a great advance in the country’s nuclear power research capabilities.

  • The HL-2M Tokamak reactor is China’s largest and most advanced nuclear fusion experimental research device, and scientists hope that the device can potentially unlock a powerful clean energy source.
  • It uses a powerful magnetic field to fuse hot plasma and can reach temperatures of over 150 million degrees Celsius, – approximately ten times hotter than the core of the sun.
  • Located in Sichuan province and completed late last year, the reactor is often called an “artificial sun” on account of the enormous heat and power it produces.

Analysis

What is 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.
  • Fusion reaction is a nuclear process by which nuclei of two light elements fuse to produce a fast, heavier nucleus and an even faster nucleon, i.e. a neutron or a proton.
  • There is a small mass difference, say m, between the initial and the final reaction products which gets converted into energy through Einstein’s equation E=mc2, c being the speed of light.
  • This energy comes out in the form of kinetic energy of the product particles and can be converted into electricity by conventional technologies.
  • For such a reaction to occur, the reacting nuclei need to have enough kinetic energy to overcome the repulsive electrostatic barrier between any two of them.
  • For this to happen in laboratory experiments, the reacting particles need to be heated to very high temperatures, more than the temperature at the core of the sun.
  • At such high temperatures, matter remains in plasma state, a collection of charged particles.
  • 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.
  • A Deuterium and a Tritium nucleus fuse to produce a Helium nucleus and a neutron.
  • In a plasma undergoing fusion, the reactions can be self-sustained, as part of the kinetic energy of the resulting charged Helium can be used to maintain the very high temperatures required to sustain the fusion reactions.
  • Three conditions must be fulfilled to achieve fusion in a laboratory:
  • very high temperature (on the order of 150,000,000° Celsius);
  • sufficient plasma particle density (to increase the likelihood that collisions do occur); and
  • 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.

The following advantages make fusion worth pursuing:

  • Abundant energy: Fusing atoms together in a controlled way releases nearly four million times more energy than a chemical reaction such as the burning of coal, oil or gas and four times as much as nuclear fission reactions (at equal mass).
  • Sustainability: Fusion fuels are widely available and nearly inexhaustible.
  • Deuterium can be distilled from all forms of water, while tritium will be produced during the fusion reaction as fusion neutrons interact with lithium.
  • Terrestrial reserves of lithium would permit the operation of fusion power plants for more than 1,000 years, while sea-based reserves of lithium would fulfil needs for millions of years.
  • No CO?: Fusion doesn’t emit harmful toxins like carbon dioxide or other greenhouse gases into the atmosphere. Its major by-product is helium: an inert, non-toxic gas.
  • No long-lived radioactive waste: Nuclear fusion reactors produce no high activity, long-lived nuclear waste.
  • Limited risk of proliferation: Fusion doesn’t employ fissile materials like uranium and plutonium.
  1. Radioactive tritium is neither a fissile nor a fissionable material.
  2. There are no enriched materials in a fusion reactor like ITER that could be exploited to make nuclear weapons.
  3. No risk of meltdown: A Fukushima-type nuclear accident is not possible in a tokamak fusion device.
  • It is difficult enough to reach and maintain the precise conditions necessary for fusion—if any disturbance occurs, the plasma cools within seconds and the reaction stops.
  • The quantity of fuel present in the vessel at any one time is enough for a few seconds only and there is no risk of a chain reaction.
  • Cost: The average cost per kilowatt of electricity is also expected to be similar to that of a fission reactor,  slightly more expensive at the beginning, when the technology is new, and less expensive as economies of scale bring the costs down.

Fission vs Fusion

  • Both fission and fusion are nuclear processes by which atoms are altered to create energy.
  • Fission is the division of one atom into two, and fusion is the combination of two lighter atoms into a larger one.
  • They are opposing processes, and therefore very different.   
  • Nuclear fission releases heat energy by splitting atoms.  
  • Nuclear fusion refers to the “union of atomic nuclei to form heavier nuclei resulting in the release of enormous amounts of energy.”
  • Both fission and fusion are nuclear reactions that produce energy.
  • Some scientists believe there are opportunities with such a power source since fusion creates less radioactive material than fission and has a nearly unlimited fuel supply.
  • However, progress is slow due to challenges with understanding how to control the reaction in a contained space.
  • Fission is used in nuclear power reactors since it can be controlled, while fusion is not utilized to produce power since the reaction is not easily controlled.