The energy cost to extract deuterium from seawater is about 1/238000th (0.00004%) the energy released from fusing that deuterium.
Nuclear fusion breeds its own tritium from lithium.
Running a 1 GW thermal fusion reactor for a year would consume $483,000 of deuterium and $1300 of lithium. At 40% conversion efficiency and 5 cents per kwh, the fusion reactor would produce $175 million of electricity in that same year.
For comparison, fuel is about 5% of the cost of electricity from fission, and about 50% the cost from coal.
Nuclear fusion breeds its own tritium from lithium.
Running a 1 GW thermal fusion reactor for a year would consume $483,000 of deuterium and $1300 of lithium. At 40% conversion efficiency and 5 cents per kwh, the fusion reactor would produce $175 million of electricity in that same year.
For comparison, fuel is about 5% of the cost of electricity from fission, and about 50% the cost from coal.