This page emphasizes the enormous physical size required for a fusion power plant and the intricate complexity of the multiple associated facilities necessary for their operation. First, there is an illustration of the enormous scale and required logistics of the ITER tokamak, which is currently under construction. Next, follows a discussion of how the component dimensions must be scaled up for the subsequent stage of a demonstration power plant, DEMO. Going beyond this scale, further, to make a Gigawatt commercial fusion reactor, which would be financially competitive with existing fission reactors, does not seem possible with the same technology.
The ITER Tokamak Complex, will be a 400,000 tonnes edifice with dimensions: 80 m tall, 120 m long and 80 m wide. As well as the tokamak, the complex will house more than 30 different plant systems that are necessary for the machine's operation. The figures below illustrate the scale of ITER.
Size of ITER Complex
Overall view of ITER site mid-2022
The ITER tokamak, of 12 m diameter, is built inside a cylindrical cryostat of 30 m height and 30 m diameter. The largest component parts before assembly are the circular poloidal coils with a 20 m diameter; the "D" shape toroidal coils measure 17 x 9 m and the vacuum vessel sectors 13 x 7 m.
First vacuum vessel sector and toroidal field coil inside the cryostat in the Tokamak pit
As well as the tokamak, the reactor operations require enormous, complex, plant systems for cooling, tritium treatment and radioactive waste processing, as indicated in the images below.
ITER, Tokamak Complex with ancillary plant systems
|ITER, Tritium processing facility||ITER, Hot cell facility|
The huge size of the ITER tokamak components requires special logistics arrangement. The poloidal coils are, in fact, too large to transport and so are constructed on-site adjacent to the tokamak building. The vacuum vessel sectors and the toroidal coils are constructed outside France and transported by sea to Marseille. Here they are transferred from ship to barge, and the barge transports them through a canal and the Etang de Berre to a port where the components are transferred to road transport for the remain trip to the ITER site. The enormous planning and special equipment necessary for the logistics need to build ITER are described on the official ITER website at The ITER Itinerary. It is likely that the scale of these components is close to the maximum which can be transported by any possible logistics.
Component for ITER tokamak being transported to site
After ITER, the progression towards commercial power reactors, is expected to pass via DEMO prototype power plants. Current plans for the EU-DEMO have a similar design as ITER with components scaled-up in linear dimensions by a factor 1.5, corresponding to volume by a factor 3.4. The electrical power output of EU-DEMO is specified as 0.5 GW, while a commercial fusion reactor would have to compete with fission reactors of 1.8 GW. While transporting DEMO parts might just be feasible with present day vehicles and roads, going bigger will not be. The cartoon below shows the relative sizes of ITER, DEMO and a projected 1 GW reactor.
Illustration of relative size of ITER, DEMO and a 1 GW Commercial Fusion Reactor.
A mainstream fusion reactor over 1 GW is clearly impossible and even 1 GW would mean the components could not be transported long distances.
Beyond the DEMO tokamak, the buildings would be enormous. The figure below shows the design for a reinforced concrete structure with dimensions of 141 m x 98 m and height 90 m, which as well as housing the tokamak, contains multiple plant systems.
DEMO Tokamak Building
The tokamak building will connect to the even larger Active Maintenance Facility, which is required to enable radioactive component replacement and waste storage. For DEMO and commercial reactors, some components would have to be replaced every few years as is described in the page, Maintenance, Breakdowns and Availability.
DEMO Active Maintenance Facility 750, 000m3.
The volume of this DEMO waste reprocessing and storage facility is 750,000m3, which can be compared to the total volume of high-level waste from all the past fission reactors in the world of 30,000 m3.
Above it has been stated that the largest commercial reactor parts could not be transported. This may be considered a show-stopper for mainstream fusion.
A possible solution might be to have on-site dedicated manufacture factories. This would facilitate several fusion reactors to be located on one site, as is the case for fission reactors. The dedicated factory would clearly increase the cost of the fusion reactors, even above the large factor of >10 for fusion compared to fission, that is estimated in the page, Cost of nuclear fusion power.
This impossible size and cost conclusion must be a strong motivation for the recent interest in Alternative Approaches to mainstream fusion.