The Ocean As A Fuel Reservoir

The world ocean is an enormous, self-renewing store of hydrogen, and the deuterium within it is the practical source of primary fusion fuel.

A planet-scale store

The ocean holds a vast mass of water, and every water molecule contains hydrogen with its fixed fraction of deuterium. Treating the ocean as a fuel reservoir, the total deuterium inventory is staggering — large enough that human energy use would draw on it at an imperceptible rate for millions of years.

Renewed by the water cycle

Water is not consumed by extracting deuterium; the depleted water returns to the environment and rejoins the hydrological cycle. The reservoir is effectively self-renewing on human timescales, and the deuterium ratio it maintains is stable. Freshwater carries the same isotope, but the ocean is the largest and most convenient source.

• The ocean's deuterium inventory is planetary in scale
• Extraction removes a negligible fraction
• Water returns to the environment after separation
• The isotope ratio is naturally maintained

From reservoir to fuel

The path from ocean to fuel is chemical separation, not extraction of a deposit, which is why the reservoir framing is apt: fusion draws fuel from a distributed store rather than mining a concentrated one. See deuterium from seawater and the water cycle and fuel.

A store that renews itself

Treating the ocean as a fuel reservoir is apt precisely because using it does not diminish it in any perceptible way. The water returns, the hydrological cycle continues, and the deuterium ratio is maintained by nature. This is unlike a mineral deposit, which is depleted as it is worked; the ocean reservoir is effectively self-renewing on every timescale relevant to human energy use.