Technology challenges for fusion power
To successfully construct and operate ITER and future advanced fusion reactors, a whole range of new technologies is being developed. Each technology represents a significant scientific or technical challenge. All these challenges must be overcome to produce an efficient and sustainable energy system.
The European Technology research programme aims at meeting the technology needs of the next generation of experimental tokamaks like ITER, and the needs of future conceptual fusion power plants such as DEMO.
Major technology projects include the development of key components such as superconducting magnetic field coils, vacuum vessel, breeder blanket and shielding, heating systems, fuel cycle, and diagnostics.
Information on heating systems, diagnostics and plasma wall interactions are covered in the Plasma engineering page.
in TOSKA at KIT © FZK
The manufacturing and testing of large-scale superconducting magnetic field coils is one of the major technology challenges for a fusion reactor.
Very strong magnetic fields are needed to confine the plasma. If conventional magnetic field coils were used, significant energy would be wasted in the form of heat generated by the high electric currents due to the resistance of the field coils.
Super conducting magnetic field coils have very low (in fact near zero) resistance when operating and do not heat up. These magnetic field coils operate at liquid helium temperature (4 K or -269 ºC), which means that the whole of magnetic system for the reactor must be cooled to just above absolute zero and operate in a vacuum. However, the super-efficiency of the superconducting magnetic field coils greatly reduces the energy required to produce the magnetic field.
The superconducting magnetic field coils also present a fabrication challenge as current superconducting alloy materials (such as the niobium/tin alloy Nb3Sn) are brittle. A single toroidal magnetic field coil may weigh a few hundred tonnes and involve several kilometres of ceramic alloy strands.
However, once the magnetic field coils are energised they can operate continually with very high efficiency, making them perfect for a steady-state fusion reactor. The magnetic field coil is one of the most expensive components of a fusion reactor and one of the most critical technologies on the path to fusion power.
The plasma containment vessel for ITER and future fusion power plants will be very large and complex components. The fabrication of these devices will raise a number of technology issues such as dimensional accuracy and welding distortion.
The future construction of advanced fusion devices requires the development of a whole range of sophisticated processes and manufacturing techniques. These include advanced welding processes, such as automated welding and inspection techniques, that can improve quality and reduce manufacturing time and cost. Several novel welding techniques have been specifically developed for the fusion programme but have very wide-ranging application in other areas.
Improvements in the manufacture of superconducting materials, including new materials able to operate at higher temperatures, will increase operating efficiencies and reliability while decreasing costs.
for ITER from TEKES © EC-RTD-EURATOM
The internal structure of a fusion reactor will become radioactive during operations due to neutron radiation and the presence of tritium. Remote-handling systems are therefore vital to be able to safely replace components such as the divertor and the breeder blanket modules inside the reactor.
A range of remote handling technologies and systems have been developed for JET using computer-controlled and operator-controlled systems. Similar systems are being developed for ITER that are capable of delicately manoeuvring components weighing up to 50 tonnes.
The design process for remote handling systems starts with a virtual prototyping in which a computer models in great detail the movements and mechanical behaviour of the robot. This helps ensure that the actual equipment will perform correctly from the very first time.
Remote handling systems for ITER have already been demonstrated on full-scale mock-ups. In particular the feasibility of remote maintenance of the divertor, including the removal and replacement of components, has been achieved.
Cryogenics and Vacuum systems
In a fusion power plant cryogenic (very low temperature) systems are used to remove impurities from the plasma, cool the superconducting magnetic field coils, separate the waste gases into their individual components for recycling or disposal, provide cooling for the radio frequency heating systems and control the pressure in the neutral beam systems.
Large-scale vacuum systems are needed to ensure ultra-high vacuum in the large reactor vessels that will be used in commercial fusion power stations, and to also maintain the vacuum necessary in the cryogenic system (cryostat) surrounding the superconducting magnetic field coils.
Such systems can also be applied to many other high-technology areas.
Breeding and Shielding blanket technology
A reliable and efficient breeder-blanket technology is vital for heat transfer and fuel generation in future fusion power plants. The high-energy neutrons released from fusion reactions do not interact with the plasma. The surrounding blanket has two main roles:
- to slow the neutrons and recover their energy for generating electricity,
- to capture the neutron and use it to transform lithium into the fusion fuel tritium.
The blanket represents a critical technology to enable fusion power. It is the medium that transforms the huge energy released by fusion into a form that can be used. It also helps generate fusion fuel in situ and shield other system components, such as the magnetic field coils, from damage caused by neutron radiation.
The blanket will need to withstand high temperatures, provide efficient heat exchange, and produce at least one tritium atom for every fusion reaction happening in the plasma.
A number of different breeder blanket concepts and configurations have been proposed. Current research is concentrating on the use of liquid-cooled lithium-lead and helium-cooled solid ceramic breeder pebbles.