The recent technological advancement in the energy front could translate into abundant low carbon energy supply; however, there are multiple problems associated with it that need to be addressed first.
This article is part of the series Comprehensive Energy Monitor: India and the World
Recent news reports suggest that fusion energy is close to a technological breakthrough. The National Ignition Facility in the US is reportedly on the verge of achieving a longstanding goal in nuclear fusion research which is to generate more energy than what is consumed. A pioneering reactor in Britain is gearing up to start pivotal tests of a fuel mix that will eventually power ITER, (International thermonuclear experimental reactor or “the way” in Latin), the world’s biggest nuclear-fusion experiment. ITER is a well-funded collaboration of 35 national governments (including India) designed to demonstrate the scientific and technological feasibility of fusion energy. Fusion has long remained the domain of government research and international collaborations, but now private investors are getting serious about nuclear fusion. 24 private-sector fusion companies in North America and Europe attracted US $300 million in investment in 2020, about 20 percent of their historical total, according to Bloomberg. Though most of the private initiatives are not close to commercial operations, some of them believe that they will break key technological barriers in fusion reactions in the next five to ten years.
In nuclear fusion, two light atomic nuclei (hydrogen or the hydrogen isotopes deuterium
Deuterium occurs naturally in seawater (30 grams per cubic metre), which makes it abundant relative to other energy resources. Tritium occurs naturally only in trace quantities (produced by cosmic rays) and is radioactive, with a half-life of around 12 years. Usable quantities can be made in a conventional nuclear reactor, or in a fusion system from lithium. Lithium is found in large quantities (30 parts per million) in the Earth’s crust and in weaker concentrations in the sea.
In a fusion reactor, neutrons generated from the D-T fusion reaction are absorbed in a blanket containing lithium which surrounds the core. The lithium is then transformed into tritium (which is used to fuel the reactor) and helium. The blanket is thick enough (about 1 metre) to slow down the high-energy neutrons. The kinetic energy of the neutrons is absorbed by the blanket, causing it to heat up. The heat energy is collected by the coolant (water, helium, or other chemical combinations) flowing through the blanket and, in a fusion power plant, this energy will be used to generate electricity by conventional methods.
For fusion reactions to take place, the repelling Coulomb forces of the nuclear constituents must be overcome, which occur at temperatures of 150 million°C (m°C). At such temperatures, the fuel is in a plasma state (superheated matter with electrons ripped away from the atoms forming an ionised gas, also known as the fourth state of matter) and needs magnetic confinement. In this stage, parameters of temperature, density, and time can be traded off against each other to achieve confinement and their optimal mix is known as the Lawson criterion. At present, two main experimental approaches to containment are being studied by government-sponsored and private nuclear fusion initiatives: Magnetic confinement fusion (MCF) and inertial confinement fusion (ICF). The first method uses strong magnetic fields to contain the hot plasma. The second involves compressing a small pellet containing fusion fuel to extremely high densities using strong lasers or particle beams.
Tokamaks, which were devised in the 1951 by Soviet physicists Andrei Sakharov and Igor Tamm are currently the dominant MCF technology used to achieve the Lawson criterion and several of the private fusion-power initiatives are using variations on the tokamak concept. A conventional tokamak is doughnut shaped with superconducting electromagnets wound around it. This contains the fuel, which is a plasma that is composed of deuterium and tritium. The magnets serve both to heat the plasma and to confine it, thus, maintaining its density and keeping it away from the torus wall, for if it touches the wall, it instantly cools down.
Tokamaks are very large devices but one of the private initiatives use a smaller one with very powerful magnets to squeeze the magnets tightly. These magnets become superconducting at relatively high temperatures, so can be cooled using liquid nitrogen, which is cheap, rather than liquid helium, which is expensive. Another fusion enterprise uses a more spherical tokamak in which the plasma remains more stable, and thus be easier to handle. The reactor has reached a plasma temperature of 15m°C which is two-thirds of the way to the 150m°C a tokamak needs to achieve the Lawson criterion. One firm is using normal hydrogen instead of deuterium and tritium and boron. Instead of a helium nucleus and a neutron, this reaction produces three helium nuclei, but this fusion reaction requires temperatures of billions of degrees. This is an order of magnitude hotter than anything achieved so far in a fusion experiment.
A combination of MCF and ICF is magnetised target fusion (MTF), also referred to as magneto-inertial fusion (MIF), is a pulsed approach to fusion and a range of MTF systems are currently being experimented with. This technology uses a magnetic field to confine a plasma with compressional heating provided by laser, electromagnetic or mechanical liner implosion. As a result of this combined approach, shorter times are required than for magnetic confinement reducing the requirement to stabilise the plasma for long periods. Conversely, compression can be achieved over timescales longer than those typical for inertial confinement, making it possible to achieve compression through mechanical, magnetic, chemical, or relatively low-powered laser drivers. Due to the reduced demands on confinement time and compression velocities, MTF has been pursued as a lower-cost and simpler approach to investigating these challenges than conventional fusion projects.
Stellarators are based on the concept of MCF, but they use non-axisymmetric coils that achieve magnetic confinement in three dimensions. Fusion can also be combined with fission in what is referred to as hybrid nuclear fusion where the blanket surrounding the core is a subcritical fission reactor. The fusion reaction acts as a source of neutrons for the surrounding blanket, where these neutrons are captured, resulting in fission reactions taking place. These fission reactions would also produce more neutrons, thereby assisting further fission reactions in the blanket. The blanket containing fission fuel in a hybrid fusion system would not require the development of new materials capable of withstanding constant neutron bombardment, whereas such materials would be needed in the blanket of a ‘conventional’ fusion system. A further advantage of a hybrid system is that the fusion part would not need to produce as many neutrons as a (non-hybrid) fusion reactor would, to generate more power than is consumed. In this case a commercial-scale fusion reactor in a hybrid system does not need to be as large as a fusion-only reactor.
The aim of the controlled fusion research is to achieve ‘ignition’, which occurs when enough fusion reactions take place for the process to become self-sustaining, with fresh fuel then being added to continue it. Once ignition is achieved, there is net energy yield.
Initiated by claims for ‘cold fusion’, research at the nanotechnology level is studying low-energy nuclear reactions (LENR) which apparently use weak nuclear interactions (rather than strong force as in nuclear fission or fusion) to create low-energy neutrons, followed by neutron capture processes resulting in isotopic change or transmutation, without the emission of strong prompt radiation. LENR experiments involve hydrogen or deuterium permeation through a catalytic layer and reaction with a metal. Researchers report that energy is released, though on any reproducible basis, very little more than is input. Over 2015–2019, Google funded 30 researchers on three projects and found no evidence that LENR is possible, but they made some advances in measurement and materials science techniques. There was some indication that the two projects involving palladium merited further study.
The aim of the controlled fusion research is to achieve ‘ignition’, which occurs when enough fusion reactions take place for the process to become self-sustaining, with fresh fuel then being added to continue it. Once ignition is achieved, there is net energy yield. According to the Massachusetts Institute of Technology (MIT), the amount of power produced increases with the square of the pressure, so doubling the pressure leads to a fourfold increase in energy production. Recent work at Osaka University’s Institute of Laser Engineering in Japan suggests that ignition may be achieved at lower temperature with a second very intense laser pulse guided through a millimetre-high gold cone into the compressed fuel and timed to coincide with the peak compression. This technique, known as ‘fast ignition’, means that fuel compression is separated from hot spot generation with ignition, making the process more practical. A completely different concept, the ‘Z-pinch’ (or ‘zeta pinch’), uses a strong electrical current in a plasma to generate X-rays, which compress a tiny D-T fuel cylinder.
While many advanced countries have national fusion programmes apart from participating in ITER, China’s fusion initiative is the one that generated headlines most recently. The Experimental Advanced Superconducting Tokamak (EAST) at China Academy of Sciences’ Hefei Institutes of Physical Science (HFIPS) produced hydrogen plasma at 50 m°C and held it for 102 seconds in 2017. In November 2018, it achieved 100 m°C for 10 seconds, with input of 10 MW (megawatt) of electric power. In July 2020, EAST achieved a completely non-inductive, current-driven, steady-state plasma for over 100 seconds, claimed as a breakthrough with significant implications for the future China Fusion Engineering Test Reactor (CFETR). In May 2021, it set a new world record of achieving a plasma temperature of 120 m°C for 101 seconds. The experiment also realised a plasma temperature of 160 m°C, lasting 20 seconds.
According to a recent study on the economics of fusion energy, the required subsidy of about 141 US $/MWh (megawatt hour) is comparable to the subsidies paid to offshore wind which totalled 136 US $/MWh in the Europe Union in 2012 in the price level of 2015 and is much lower than the subsidies provided in the same year for photovoltaic plants in the amount of 249 US $/MWh in 2015 price level. These subsidies to renewable resources do not include the costs of maintaining large standby power plants running on coal, gas, or pumping hydroelectric power stations, which in the case of fusion plants will not be necessary. According to the study, the levelised cost of energy (LCOE) of fusion sources is higher than the average LCOE of nuclear and fossil power plants but lower than the average LCOE of the photovoltaic power plants. Accounting for the external costs (climate change, human health costs, nuclear safety, energy security, etc.), the total cost of energy (TCOE) that includes LCOE and external costs of fusion power plants is second lowest after nuclear fission.
To date, none of the projects have produced a fusion reaction that creates significantly more energy than it consumes. But if it is achieved, it will mean abundant low carbon energy supply for the world. Each D-T fusion event releases 17.6 MeV (million electron Volt) which on a mass basis, is over four times as much energy as uranium fission. The energy density of fusion reactions in gas is less than for fission reactions in solid fuel, and the heat yield per reaction is 70 times less. Thus, thermonuclear fusion will always have a much lower power density than nuclear fission, which means that any fusion reactor needs to be larger, and therefore, costlier than a fission reactor of the same power output. In addition, nuclear fission reactors use solid fuel, which is denser than a thermonuclear plasma, so the energy released is more concentrated. Also, the neutron energy from fusion is higher than from fission, 14.1 MeV instead of about 2 MeV, which presents significant challenges regarding structural materials.
1 gram of fusion fuel corresponds to that of 12 tonnes of coal. This means that India would need only about 70 tonnes of fusion fuel annually to replace coal in power generation completely. Roughly 55,000 barrels of oil is required to heat 10,000 modern western homes for one year. With fusion energy, it would take one litre of deuterium and tritium, extracted from water to power those 10,000 homes. And whereas those 55,000 barrels of oil would release 23,500 tons of carbon dioxide (CO2), fusion produces no emissions and will have a lifecycle carbon intensity lower than solar or wind (as measured in CO2 from all construction, manufacturing, and operations per kWh
With fusion, there would be no danger of a runaway reaction as this is intrinsically impossible and any malfunction would result in a rapid shutdown of the plant. Although fusion does not generate long-lived radioactive products and the unburned gases can be treated on site, there would a short- to medium-term radioactive waste problem due to activation of the structural materials. Some component materials will become radioactive during the lifetime of a reactor, due to bombardment with high-energy neutrons, and will eventually become radioactive waste. The volume of such waste is comparable to corresponding volumes from fission reactors. However, the long-term radiotoxicity of the fusion wastes would be considerably lower than that from actinides in used fission fuel, and the activation product wastes would be handled in much the same way as those from fission reactors with some years of operation.
While fusion power clearly has much to offer when the technology is eventually developed, the problems associated with it also need to be addressed if it is to become a widely used future energy source.
There are also other concerns, principally regarding the possible release of tritium into the environment. It is radioactive and very difficult to contain since it can penetrate concrete, rubber, and some grades of steel. As an isotope of hydrogen, it is easily incorporated into water, making the water itself weakly radioactive. With a half-life of over 12 years, the presence of tritium remains a threat to health for about 125 years after it is created, as a gas or in water, if at high levels. It can be inhaled, absorbed through the skin or ingested. Inhaled tritium spreads throughout the soft tissues and tritiated water mixes quickly with all the water in the body. Although there is only a small inventory of tritium in a fusion reactor, a few grams, each could conceivably release significant quantities of tritium during operation through routine leaks, assuming the best containment systems. An accident could release even more. This is one reason why long-term hopes are for the deuterium-deuterium fusion process, dispensing with tritium. While fusion power clearly has much to offer when the technology is eventually developed, the problems associated with it also need to be addressed if it is to become a widely used future energy source.
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