First let’s look at the order of magnitude kind of cost we can expect. Nuclear fission technology is about 80 years old and by all standards a fairly mature technology, even considering the latest reactor designs like advanced boiling water reactors (ABWR). The largest nuclear power plant in the world is Japan’s Kashiwazaki–Kariwa NPP which as seven reactors for a total generating capacity of 8 GW (8,000 MW). From ground breaking to first power generation took more than four years. The last reactor did not come online until 12 years after the first one requiring huge capital outlays before revenue could be collected by selling the generated power. The average cost per kW of electricity generated is about $5,000 or a total of $40 billion to build the entire complex.
- Trident nuclear missile submarine – $3 billion
- Nimitz class nuclear powered aircraft carrier – $6.2 billion
- Lifetime cost of Space Shuttle program – $200 billion ($1.5 billion / flight)
The International Thermonuclear Experimental Reactor (ITER), the only commercial fusion reactor program currently funded has an estimated price of $18 billion. (The US National Ignition Facility, the only fusion project in the US, is changing priorities after failing to meet the goal of "ignition" when the latest round of funding ended this last September.) It’s designed net power generation is 450 MW. This is only 5% of the power generated by Kashiwazaki–Kariwa NPP for almost half the cost. So even assuming ITER is a complete success, which is doubtful considering the immature state of the technology, it will not be economically viable. But it is a demonstration of the technology, so economics are not the primary objective.
However, the outlook for fusion gets worse. The economies of scale required for a large fusion reactor demand generation on the order of 5 – 10 GW. This falls out of a complex analysis of cost for power generation that ranges from $2000 / kW for state-of-the art pulverized coal plants to $10,000 / kW for the latest ABWR nuclear fission power plants. In order to be economically viable, a fusion power plant has to deliver power within this price band. For maximum economies of scale, at $10,000 / kW for a total of 10 GW power generation, this equates to a total lifetime cost (capital, operating, fuel and financing) of less than $100 billion. For a 20 year lifetime, this would approximate to $80 billion to build and $1 billion annual costs. And this would make the electricity one of the most expensive sources. To come down to the $2000 / kW of coal fired plants, the build cost would have to come down to about $16 billion. That’s already less than the projected ITER cost for only 450 MW of generation.
There are few aspects of the technology required to fuse hydrogen atoms that indicate orders of magnitude cost reduction over time. Compare the costs of the largest partical colliders as they have grown in size over the last 20 years. The closest parallel technology on the electric power generation front is the evolution of nuclear fission power plants. Even at the enormous economies of scale afforded by Kashiwazaki–Kariwa NPP its cost per kW is still in the middle of the cost band for electrical generation sources. Most of the worlds nuclear power plants fall in the upper reaches of this price band. So even under the very best of technological circumstances, fusion power will never be a viable source of electrical power generation purely for economic reasons.