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.
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.
- Radioactive tritium is neither a fissile nor a fissionable material.
- There are no enriched materials in a fusion reactor like ITER that could be exploited to make nuclear weapons.
- 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.