This page emphasizes the enormous physical size required for fusion power plants and the intricate complexity of the multiple associated facilities necessary for their operation. 

The discussion starts with how ITER is being constructed, at the present time, and moves on to how this must be scaled up tremendously for the next stage demonstrator reactors and how scaling beyond that for a commercial power plant seems unlikely.

ITER dimensions

The ITER Tokamak Complex, will be a 400,000 t 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.

Overall view of ITER site mid-2022

First vacuum vessel sector and toroidal field coils in Tokamak pit

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.

As well as the tokamak, the reactor operations required enormous, complex, plant systems for cooling, tritium treatment and radioactive waste processing.

ITER, Tokamak Complex with ancillary plant systems

ITER, Tritium processing facilityITER, Hot cell facility

ITER logistics

The enormous size of these components requires special logistics arrangement. The poloidal coils are, in fact, too large to transport and so 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 in and the barge transports them through a canal and the Etang de Berre 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 can be found on the official ITER website; The ITER Itinerary

It seems likely that the scale of these components is close to the maximum which can be transport by this way or any other possible logistics.

Scale of commercial power reactors

After ITER, the progression towards commercial power reactors, is expected to pass via DEMO prototype reactors. Current plans for the EU-DEMO have similar elements as ITER, scaled-up in linear dimensions by a factor 1.5 and volume, so weight, by a factor 3.4. Further, the electrical power output of EU-DEMO is specified as 0.5 GW, while a commercial fusion reactor may 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. Hence, a simple scale-up of reactor size to achieve over 1 GW with the same technology is clearly impossible. The options for a commercial reactor must be either less power output or a significantly different design.

The DEMO tokamak building is an enormous reinforced concrete structure with dimensions of L=141m x W=98m, H=90m, which as well as housing the tokamak, contains multiple plant systems as indicated in the image below. The tokamak complex connects to the even larger Active Maintenance Facility described later.

DEMO Tokamak Building

Radioactive waste handling facilities

All fusion power plants will require enormous facilities to handle radioactive waste. For ITER the components inside the vacuum vessel will be replaced once during the tokamak lifetime. For DEMO and commercial reactors, the components would have to be replaced every few years.

DEMO Active Maintenance Facility 750, 000m3.

The volume of this DEMO waste reprocessing and storage facility for one prototype fusion reactor 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.

Commercial fusion site with multiple sites and dedicated reactors?

The conclusion above is that with an ITER-like design, the largest commercial reactor parts could not be transported. So, a solution could be to to have on-site dedicated manufacture factories. Anyway, to ever replace a fission reactor economy there would have to be multiple small output fusion reactors to make up for the replaced fission output. Hence, special factories making parts locally for 10-20 fusion reactors might be the best economic solution. In addition looking at the enormous planned active maintenance facility for one DEMO plant, it could well be economically optimal to make one enormous reprocessing and storage facility.

If the technology actually ever works, this seems like the only possible solution for commercialization.