www.foronuclear.org MONOGRAPH Nuclear Fusion: An Energy Source for the Future Unlike fission power, which involves The fuel for fusion reactors consists of splitting very heavy atoms to relea- two isotopes of hydrogen gas: deute- se energy, i.e. the reaction that takes rium and tritium. Thus, a fusion power place in all nuclear power stations cu- plant will utilize a fuel that is available rrently in operation around the world, in nearly unlimited amounts on Earth fusion releases energy as a result of and will not give off greenhouse ga- two light atoms binding together. ses or give rise to long-lived radioac- tive waste. Fusion could provide a large-scale, sustainable and continuous energy supply The current goal of nuclear fusion second 600 million tonnes of hydro- research reactors such as that of the gen fuse and form helium. ITER project — which we will discuss However, here on Earth fusion will ne- below — is to use nuclear fusion as it cessarily take place at a much modest takes place in the Sun or the stars as scale, so the temperatures that need a power source here on Earth. Inside to be achieved inside fusion reactors the Sun, hydrogen atoms collide and must be much higher — in the or- combine with each other at incredi- der of 100M degrees Celsius — so as bly high temperatures — close to 15M to be able to have a technically viable degrees Celsius — and are subjected power source. to huge gravitational pressures: every MONOGRAPH Nuclear fusion 1 MONOGRAPH Technological requirements Harnessing fusion power requires lled in order to fuse them into hea- developing technological systems vier ones. that meet two basic requirements: • Confining matter to keep it in an • Heating hydrogen to temperatu- ionized gas or plasma state by en- Heating matter to millions of degrees Celsius and res of millions of degrees Celsius to closing it inside the reactor cavity confining it are two of the technological requirements produce an overheated gas or plas- long enough for it to react. for achieving nuclear fusion ma in which electrons leave their orbitals and nuclei can be contro- Main lines of development There are two main lines of develop- dense that particles hardly have a ment of fusion technology: chance to escape without reacting with each other. After being sud- • Magnetic confinement fusion. denly hit by powerful laser-created The electrically charged particles light beams, a small sphere of a in the plasma are trapped inside a solid deuterium-and-lithium com- space delimited by a magnetic field pound implodes due to the effect and forced to move along helical pa- of the shock wave. Thus, it becomes ths determined by the latter’s lines hundreds of times denser than in of force. The most developed device its normal solid state and explodes at the moment is toroidal-shaped as a result of the fusion reaction. and known as tokamak — the tech- nology used in the ITER project. • Inertial confinement fusion. It consists in creating a medium so Source: ITER MONOGRAPH Nuclear fusion 2 MONOGRAPH Technical considerations The different possible reactors for in nature. Even for this reaction, the carrying out nuclear fusion requi- required temperatures are incredi- re reaching different temperature bly high as they exceed 100M de- and density values to achieve op- grees Celsius. timal efficiency. Current studies Fusion with deuterium and tritium focus mostly on the reaction of consists in the merging of their nu- two isotopes of hydrogen — deu- clei — according to a process similar terium and tritium — because it is to the one that happens inside the one of the easiest to create and its Sun — to produce an alpha particle components the easiest to obtain: with a nucleus of helium (He4) con- Deuterium directly from water, and sisting of two neutrons and two pro- tritium inside the reactor itself by tons, as shown in the picture below: neutron bombardment of a layer of lithium, which is also very abundant If we apply Einstein’s equation (E clei must move at sufficiently high = m·c2) to the mass difference, we speeds, something which requires a can see that there is a large amount very high temperature. of energy potentially available per At very high temperatures, matter is reaction (17.6 MeV) — even after in a state known as plasma in which subtracting the necessary energy electrons cease to be bound to their for nuclear fusion to be self-sustai- atomic nuclei. Furthermore, in or- ning. The net difference is still big der for a sufficiently large number and is one of the main appeals of of fusion reactions to occur, there fusion. must be a lot, i.e. a high density, of The two light nuclei that under- atomic nuclei, which must remain go fusion are positively charged in this situation long enough for and hence repel each other. In or- the reactions among them to occur. der to overcome this repulsion for- Under these conditions, the plasma ce so that the strong nuclear force is said to be “confined.” — which is always a short-range attraction force — can act, the nu- MONOGRAPH Nuclear fusion 3 MONOGRAPH Advantages & challenges Nuclear fusion might become a Nuclear fusion, however, also poses large-scale energy resource in the some challenges: second half of this century and has big advantages compared to other • It is still a long way away from power sources: commercial availability. The biggest project — the ITER experimental fu- • Safety. Since the fusion reaction is sion reactor — aims to prove that a not a chain reaction, control thereof large-scale, self-sustaining fusion cannot be lost. The reaction can be reaction is possible. Once success is stopped at any time by simply cut- achieved, an electricity producing ting off the fuel supply. demonstration reactor will have to be built, which pushes the project’s • Abundant cheap fuel. It is unifor- horizon to the end of this century. mly geographically distributed, and This timespan may be shortened if there is enough of it in the water of the SPARC (Scalable Processor AR- all the oceans and lakes for millions Chitecture) project — discussed be- of years based on current energy low — is successful. consumption levels. • High costs. The high costs of fu- Source: ITER • Clean energy. The resulting gases sion technology put it out of reach from the reaction do not contribu- of private initiatives. At this time, te to the greenhouse effect. The ra- development is taking place at the dioactivity of the reactor’s structure scale of agreements among the go- — caused by the neutrons released vernments of several nations. This during the fusion reactions — can difficulty could be reduced if the The first demonstration reactor for producing electricity be minimized by carefully choosing projected advancements in high by fusion could be a reality by the end of this century low activation materials. Therefore, temperature superconductors fina- the elements of the reactor do not lly take place. need to be stored for more than 50 years. MONOGRAPH Nuclear fusion 4 MONOGRAPH THE ITER PROJECT The purpose of the ITER (Interna- The ITER will be the first fusion tional Thermonuclear Experimen- facility capable of producing net tal Reactor) is to determine the te- energy and maintaining the fusion chnological and financial viability process over long periods of time of magnetic confinement nuclear as well as of testing all necessary fusion as a large-scale, CO2-free technology and materials, thus re- power source — albeit without ge- presenting a preliminary stage to nerating electrical power yet. the construction of a commercial demonstration facility. The purpose of the ITER is to determine the technological and financial viability of magnetic confinement nuclear fusion as a large-scale, CO2-free power source Sources: ITER and Foro Nuclear MONOGRAPH Nuclear fusion 5 MONOGRAPH The ITER is currently being built in place, and the first plasma will be 35 countries participate in the ITER Fusion Project Cadarache, Southern France, and achieved, in 2025, once construction under construction in France, including Spain through is a collaboration among 35 coun- is completed in 2024. This will be the European Union tries integrated in 7 main blocs: Chi- the phase prior to operation, whose na, the EU (through Euratom), India, planned duration is 20 years. Japan, South Korea, Russia, and the U.S. The first reactor tests will take When the agreement for its deve- lopment was signed in 2006, the countries taking part in the project undertook to share all building, operating and dismantling costs as well as the experimental results and any resulting intellectual property. The total cost of construction cu- rrently stands at around €23,500M. The European Union is responsible for 45.6% of the funding (more than €10,700M), a commitment it meets via funds managed by Fusion for Energy (F4E), a EU body headquar- tered in Barcelona. France, as the host country, provides approximate- ly 20% of this sum. 90 percent of all contributions are in kind. The pro- ject’s other six members contribute equally to the rest of the budget. Source: ITER Source: ITER MONOGRAPH Nuclear fusion 6 MONOGRAPH The principal piece of equipment is the plasma thus generated. The plas- a tokamak-shaped reactor, inside of ma’s electrically charged particles will which the fusion energy will be ab- conform to the shape of the powerful sorbed through the vessel’s walls as magnetic field created by the coils si- heat. This heat will then be used to tuated around the vessel — which are generate steam and, with the latter, kept at cryogenic temperatures near electricity in turbo-alternators. absolute zero (-273 °C) — and remain confined in it without touching the The heart of the tokamak is its toroidal walls of the latter, which cannot wi- vacuum chamber in which deuterium thstand their high temperature.