If no further cost increases happen and everything works according to the plan, in a few years ITER will be able to produce 500 MW of heat (not electricity). This heat will just be released to the atmosphere without producing any useful electricity (ITER will not even have an electrical generator). This heat dump into the atmosphere is planned to take place during 2035 if no additional delays occur.
The input for producing this output is calculated to be 50 MW of heat. However, since the input heat will be produced with electricity, at a 40% efficiency for the generator it actually requires a thermal input of 50 / 0.40 = 125 MW of heat. So the net heat production of ITER should be 500 MW - 125 MW = 375 MW. If this heat were used to power an electrical generator (at say, 40% efficiency) its output would be 150 MW.
The cost of ITER, so far, is projected to be 20 billion euros, so per GWe of capacity it corresponds to 20 / 0.125 = 160 billion euros. And again, this cost does not include boilers, generator, transformers, etc.
160 billion euros per GWe is 20 times or more the current capital investment in a fission reactor. In order for fusion to compete in the marketplace at least 95% of the cost of the reactor will have to be cut for it to be attractive to electric utilities. Yes, there will be a learning curve but the magnitude of the cost reduction required seems challenging, to say the least. At the same time, fission is a moving target.
Also, a fusion reactor might not be as long lived as an equivalent fission one. "A technical concern is that the 14 MeV neutrons produced by the fusion reactions will damage the materials from which the reactor is built."
Plus, since it is inherently more complex, its capacity factor would almost certainly be lower than that of a fission reactor (in the US the whole nuclear fleet operates at around 90% annual capacity factor).
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