![EUROfusion schematic diagram of fusion power plant](https://upload.wikimedia.org/wikipedia/commons/e/e9/EUROfusion_schematic_diagram_of_fusion_power_plant.jpg)
DEMO refers to a proposed class of
nuclear fusion
Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manifest ...
experimental reactors that are intended to demonstrate the
net production of electric power from nuclear fusion. Most of the
ITER
ITER (initially the International Thermonuclear Experimental Reactor, ''iter'' meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at creating energy by replicating, on Earth ...
partners have plans for their own DEMO-class reactors. With the possible exception of the EU and Japan, there are no plans for international collaboration as there was with ITER.
Plans for DEMO-class reactors are intended to build upon the
ITER
ITER (initially the International Thermonuclear Experimental Reactor, ''iter'' meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at creating energy by replicating, on Earth ...
experimental nuclear fusion reactor.
The most well-known and documented DEMO-class reactor design is that of the European Union (EU). The following parameters have been used as a baseline for design studies: the EU DEMO should produce at least 2000 megawatts (2
gigawatt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Wat ...
s) of
fusion power
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion, nuclear fusion reactions. In a fusion process, two lighter atomic nucleus, atomic nuclei combine to form a heavier nucleus, whi ...
on a continuous basis, and it should produce 25 times as much power as required for scientific breakeven, which does not include the power required to operate the reactor. The EU DEMO design of 2 to 4 gigawatts of thermal output will be on the scale of a modern
electric power
Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions o ...
station.
However, the nominal value of the steam turbine is 790 megawatts, which, after overcoming a 5% loss because of the coupling from the turbine to the synchronous generator, results in a nominal value for electrical power output of approximately 750 megawatts.
:5
To achieve its goals, if utilizing a conventional tokamak design, a DEMO reactor must have
linear
Linearity is the property of a mathematical relationship (''function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear r ...
dimensions about
15% larger than ITER, and a
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
density about 30% greater than ITER. According to timeline from
EUROfusion
EUROfusion is a consortium of national fusion research institutes located in the European Union, the UK, Switzerland and Ukraine. It was established in 2014 to succeed the European Fusion Development Agreement ( EFDA) as the umbrella organisation o ...
, operation is planned to begin in 2051.
It is estimated that subsequent commercial fusion reactors could be built for about a quarter of the cost of DEMO.
However, the ITER experience suggests that development of a multi-billion US dollar tokamak-based technology innovation cycle able to develop
fusion power
Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion, nuclear fusion reactions. In a fusion process, two lighter atomic nucleus, atomic nuclei combine to form a heavier nucleus, whi ...
stations that can compete with non-fusion energy technologies is likely to encounter the "valley of death" problem in
venture capital
Venture capital (often abbreviated as VC) is a form of private equity financing that is provided by venture capital firms or funds to startups, early-stage, and emerging companies that have been deemed to have high growth potential or which ha ...
, i.e., insufficient investment to go beyond prototypes, as DEMO tokamaks will need to develop new supply chains and are labor intensive.
DEMO's place in the development of fusion power
The 2019 US
National Academies of Sciences, Engineering, and Medicine 'Final Report of the Committee on a Strategic Plan for U. S. Burning Plasma Research' noted, "a large DEMO device no longer appears to be the best long-term goal for the U.S. program. Instead, science and technology innovations and the growing interest and potential for private-sector ventures to advance fusion energy concepts and technologies suggest that smaller, more compact facilities would better attract industrial participation and shorten the time and lower the cost of the development path to commercial fusion energy". Approximately two dozen private-sector companies are now aiming to develop their own fusion reactors within the DEMO roadmap timetable. The US appears to be working towards one or more national DEMO-class fusion power plants on a cost-sharing basis.
The 3 October 2019 UK Atomic Energy announcement of its
Spherical Tokamak for Energy Production
Spherical Tokamak for Energy Production (STEP) is a spherical tokamak fusion plant concept proposed by the United Kingdom Atomic Energy Authority and funded by UK government. The project is a proposed DEMO-class successor device to the ITER tokam ...
(STEP) grid-connected reactor for 2040 suggests a combined DEMO/PROTO phase machine apparently to be designed to
leapfrog
Leapfrog is a children's game in which players vault over each other's stooped backs.
History
Games of this sort have been called by this name since at least the late sixteenth century.CFETR
The China Fusion Engineering Test Reactor (中国聚变工程实验堆, CFETR) is a proposed tokamak fusion reactor, which uses a magnetic field in order to confine plasma and generate energy.
Presently, tokamak devices are leading candidates fo ...
machine, a grid-connected gigawatt-generating reactor, overlaps the DEMO timetable. Japan also has plans for a DEMO reactor, the JA-DEMO, via its upgraded
JT-60
JT-60 (short for Japan Torus-60) is a large research tokamak, the flagship of Japan's magnetic fusion program, previously run by the Japan Atomic Energy Research Institute (JAERI) and currently run by the Japan Atomic Energy Agency's (JAEA) Naka ...
, as does South Korea (K-DEMO).
In November 2020, an independent expert panel reviewed
EUROfusion
EUROfusion is a consortium of national fusion research institutes located in the European Union, the UK, Switzerland and Ukraine. It was established in 2014 to succeed the European Fusion Development Agreement ( EFDA) as the umbrella organisation o ...
's design and R&D work on the EU's DEMO, and EUROfusion confirmed it was proceeding with the next step of its Roadmap to Fusion Energy, namely the conceptual design of a DEMO in partnership with the European fusion community and industry, suggesting an EU-backed DEMO-phase machine that could formally bear the DEMO name.
In June 2021, General Fusion announced it would accept the UK government's offer to host the world's first substantial
public-private partnership fusion demonstration plant, at
Culham Centre for Fusion Energy
The Culham Centre for Fusion Energy (CCFE) is the UK's national laboratory for fusion research. It is located at the Culham Science Centre, near Culham, Oxfordshire, and is the site of the Joint European Torus (JET), Mega Ampere Spherical Tokam ...
. The plant will be constructed from 2022 to 2025 and is intended to lead the way for commercial pilot plants in the late 2020s. The plant will be 70% of full scale and is expected to attain a stable plasma of 150 million degrees.
History of the concept
The DEMO reactor concept goes back to the 1970s. A graph by W.M. Stacey shows that by 1979, there were completed DEMO designs by
General Atomics
General Atomics is an American energy and defense corporation headquartered in San Diego, California, specializing in research and technology development. This includes physics research in support of nuclear fission and nuclear fusion energy. The ...
and
Oak Ridge National Laboratory
Oak Ridge National Laboratory (ORNL) is a U.S. multiprogram science and technology national laboratory sponsored by the U.S. Department of Energy (DOE) and administered, managed, and operated by UT–Battelle as a federally funded research and ...
.
At a June 1986 meeting organized by the IAEA, participants agreed on the following, concise definition for a DEMO reactor: "The DEMO is a complete electric power station demonstrating that all technologies required for a prototype commercial reactor work reliably enough to develop sufficient confidence for such commercial reactors to be competitive with other energy sources. The DEMO does not need to be economic itself nor does it have to be full scale reactor size."
The following year, an IAEA document shows design parameters for a DEMO reactor in the US by Argonne National Laboratory, a DEMO reactor in Italy called FINTOR, (Frascati, Ispra, Napoli Tokamak Reactor), a DEMO reactor at Culham (UK), and a European DEMO reactor called NET (Next European Torus). The major parameters of NET were 628 MW net electrical power and 2200 MW gross thermal power output, nearly the same as the current EU DEMO design.
Timeline
The EU DEMO timeline has slipped several times, following slippage in the ITER timetable. The following timetable was presented at the IAEA Fusion Energy Conference in 2004 by
Christopher Llewellyn Smith
Sir Christopher Hubert Llewellyn Smith (born 19 November 1942) is an Emeritus Professor of Physics at the University of Oxford.
Education
Llewellyn Smith was educated at the University of Oxford (BA) and completed his Doctor of Philosophy degr ...
:
*Conceptual design was completed in 2017
*Engineering design is to be complete by 2024 (after input from ITER D-T tests, and data from
IFMIF
The International Fusion Materials Irradiation Facility, also known as IFMIF, is a projected material testing facility in which candidate materials for the use in an energy producing fusion reactor can be fully qualified. IFMIF will be an acceler ...
- both delayed )
*The first construction phase is to last from 2024 to 2033
*The first phase of operation is to last from 2033 to 2038
*The station is then to be expanded and updated (e.g. with phase 2 blanket design)
*The second phase of operation is to start in 2040
In 2012,
European Fusion Development Agreement
EFDA (1999 — 2013) has been followed by EUROfusion, which is a consortium of national fusion research institutes located in the European Union and Switzerland.
The European Union has a strongly coordinated nuclear fusion research programme. At ...
(EFDA) presented a roadmap to fusion power with a plan showing the dependencies of DEMO activities on ITER and IFMIF.
[Fusion Electricity - A roadmap to the realisation of fusion energy]
EFDA 2012 - 8 missions, ITER, DEMO, project plan with dependencies, ...
* Conceptual design to be complete in 2020
[
* Engineering design complete, and decision to build, in 2030
* Construction from 2031 to 2043
* Operation from 2044, Electricity generation demonstration 2048
This 2012 roadmap was intended to be updated in 2015 and 2019.][ The EFDA was superseded by ]EUROfusion
EUROfusion is a consortium of national fusion research institutes located in the European Union, the UK, Switzerland and Ukraine. It was established in 2014 to succeed the European Fusion Development Agreement ( EFDA) as the umbrella organisation o ...
in 2013. The roadmap was subsequently updated in 2018.
* Conceptual design to be complete before 2030
* Engineering design 2030-2040
* Construction from 2040
This would imply operations commencing sometime in the 2050s.
Technical considerations
When deuterium
Deuterium (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...
and tritium
Tritium ( or , ) or hydrogen-3 (symbol T or H) is a rare and radioactive isotope of hydrogen with half-life about 12 years. The nucleus of tritium (t, sometimes called a ''triton'') contains one proton and two neutrons, whereas the nucleus o ...
fuse, the two nuclei come together to form a resonant state which splits to form in turn a helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
nucleus (an alpha particle
Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produce ...
) and a high-energy neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
.
: + → + + 17.6 MeV
DEMO will be constructed once designs which solve the many problems of current fusion reactors are engineered. These problems include: containing the plasma fuel at high temperatures, maintaining a great enough density of reacting ions, and capturing high-energy neutrons from the reaction without melting the walls of the reactor.
*The activation energy for fusion is very large because the proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s in each nucleus strongly repel one another; they are both positively charged. In order to fuse, the nuclei must be within 1 femtometre
The magnitudes_.html" ;"title="Magnitude_(mathematics).html" ;"title="atom.html" ;"title="helium helium_atom_and_perspective_Magnitude_(mathematics)">magnitudes_">Magnitude_(mathematics).html"_;"title="atom.html"_;"title="helium_atom">helium_at ...
(1 × 10−15 metres) of each other, where quantum-tunnelling effects permit the parent nuclei to fuse together into the resonant state. The principle is to form a quasi-Maxwellian distribution for the deuterons and the tritons, at very high temperatures, where the nuclei in the tail of the Maxwellian undergo fusion, while the continuous elastic collisions among the other nuclei will not alter the state of the plasma.
*DEMO, a Tokamak
A tokamak (; russian: токамáк; otk, 𐱃𐰸𐰢𐰴, Toḳamaḳ) is a device which uses a powerful magnetic field to confine plasma in the shape of a torus. The tokamak is one of several types of magnetic confinement devices being d ...
reactor, requires both dense plasma and high temperatures for the fusion reaction to be sustained.
*High temperatures
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied o ...
give the nuclei enough energy to overcome their electrostatic repulsion
Electrostatics is a branch of physics that studies electric charges at rest ( static electricity).
Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for a ...
. This requires temperatures in the region of 100 MK, and is achieved using energy from various sources, including Ohmic heating
Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor produces heat.
Joule's first law (also just Joule's law), also known in countries of former US ...
(from electric currents induced in the plasma), microwaves
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency rang ...
, ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
beams, or neutral beam injection.
*Containment vessels melt at these temperatures, so the plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
is to be kept away from the walls using magnetic confinement
Magnetic confinement fusion is an approach to generate thermonuclear fusion power that uses magnetic fields to confine fusion fuel in the form of a plasma. Magnetic confinement is one of two major branches of fusion energy research, along with ...
.
Once fusion has begun, high-energy neutrons at about 160 GK will flood out of the plasma along with X-rays
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 Picometre, picometers to 10 Nanometre, nanometers, corresponding to frequency, ...
, neither being affected by the strong magnetic fields. Since neutrons receive the majority of the energy from the fusion, they will be the reactor's main source of thermal energy output. The ultra-hot helium product at roughly 40GK will remain behind (temporarily) to heat the plasma, and must make up for all the loss mechanisms (mostly bremsstrahlung
''Bremsstrahlung'' (), from "to brake" and "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typicall ...
X-rays from electron deceleration) which tend to cool the plasma rather quickly.
*The Tokamak containment vessel will have a lining composed of ceramic or composite tiles containing tubes in which warm liquid lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
metal will flow, cooling the lining.
*Lithium readily absorbs high-speed neutrons to form helium and tritium, becoming hot in the process.
*This increase in temperature is passed on to another (intermediate) coolant, possibly (pressurized) liquid water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
in a sealed, pressurized pipe.
*Heat from the intermediate coolant will be used to boil water in a heat exchanger
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
.
*Steam from the heat exchanger will be used to drive turbines and generators, to create electric current
An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
.
*Waste heat energy in excess of the generated electrical energy is dumped into the environment.
*Helium byproduct is the "ash" of this fusion, and will not be allowed to accumulate too much in the plasma.
*Carefully measured amounts of deuterium and tritium are added back into the plasma and heated.
*The lithium is processed to remove the helium and tritium, with the balance recycled to collect more heat and neutrons. Only a tiny amount of lithium is consumed.
The DEMO project is planned to build upon and improve the concepts of ITER. Since it is only proposed at this time, many of the details, including heating methods and the method for the capture of high-energy neutrons, are still undetermined.
Conceptual design
All aspects of DEMO were discussed in detail in a 2009 document by the Euratom-UKAEA Fusion Association.[DEMO and the Route to Fusion Power, Derek Stork, Euratom-UKAEA Fusion Association, September 2009]
/ref>
Four conceptual designs PPCS A,B,C,D were studied. Challenges identified included:[
* structural materials resistant to the high neutron flux
* ]high-temperature superconductors
High-temperature superconductors (abbreviated high-c or HTS) are defined as materials that behave as superconductors at temperatures above , the boiling point of liquid nitrogen. The adjective "high temperature" is only in respect to previo ...
, to avoid the need for large amounts of helium for cooling, that would challenge world helium reserves
* need for high efficiency in the heating and current drive systems.
In the 2012 timeline, the conceptual design should be completed in 2020.
Radioactive waste
While fusion reactors like ITER and DEMO will produce neither transuranic
The transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92, which is the atomic number of uranium. All of these elements are unstable and decay radioactively into other elements. ...
nor fission product
Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release ...
wastes, which together make up the bulk of the nuclear waste
Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, rare-earth mining, and nuclear weapons r ...
s produced by fission reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from ...
s, some of the components of the ITER and DEMO reactors will become radioactive due to neutrons impinging upon them. It is hoped that plasma facing material
In nuclear fusion power research, the plasma-facing material (or materials) (PFM) is any material used to construct the plasma-facing components (PFC), those components exposed to the plasma within which nuclear fusion occurs, and particularly t ...
s will be developed so that wastes produced in this way will have much shorter half lives
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
than the waste from fission reactors, with wastes remaining harmful for less than one century. Development of these materials is the prime purpose of the International Fusion Materials Irradiation Facility
The International Fusion Materials Irradiation Facility, also known as IFMIF, is a projected material testing facility in which candidate materials for the use in an energy producing fusion reactor can be fully qualified. IFMIF will be an acceler ...
. The process of manufacturing tritium currently produces long-lived waste, but both ITER and DEMO will produce their own tritium, dispensing with the fission reactor currently used for this purpose.
PROTO
PROTO was a proposal for a beyond-DEMO experiment, part of the European Commission
The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body o ...
long-term strategy for research of fusion energy. PROTO would act as a prototype power station, taking in any remaining technology refinements, and demonstrating electricity generation on a commercial basis. It was only expected after DEMO, beyond 2050, and probably will not be the second part of a DEMO/PROTO experiment as it no longer appears in official documentation.The roadmap to magnetic confinement fusion, Damian Hampshire
2008 - Says ITER and IFMIF will be completed in 2016
See also
*China Fusion Engineering Test Reactor
The China Fusion Engineering Test Reactor (中国聚变工程实验堆, CFETR) is a proposed tokamak fusion reactor, which uses a magnetic field in order to confine plasma and generate energy.
Presently, tokamak devices are leading candidates fo ...
*COLEX process The COLEX process (or COLEX separation) is a chemical method of isotopic separation of lithium-6 and lithium-7, based on the use of mercury. COLEX stands for column exchange.
Since the beginning of the atomic era, a variety of lithium enrichments ...
*ITER
ITER (initially the International Thermonuclear Experimental Reactor, ''iter'' meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at creating energy by replicating, on Earth ...
*PROTO
Proto or PROTO may refer to:
Language
* Proto-, an English prefix meaning "first"
Media
* ''Proto'' (magazine), an American science magazine
* Radio Proto in Cyprus
Music
* ''Proto'' (Holly Herndon album), 2019
* ''Proto'' (Leo O'Kelly ...
*Spherical Tokamak for Energy Production
Spherical Tokamak for Energy Production (STEP) is a spherical tokamak fusion plant concept proposed by the United Kingdom Atomic Energy Authority and funded by UK government. The project is a proposed DEMO-class successor device to the ITER tokam ...
References
{{fusion experiments
Tokamaks
Proposed nuclear power stations
Proposed fusion reactors
ITER