Is nuclear fusion a sustainable energy form?

An acceptable criterion for strong sustainability in the consumption of natural resources is an effective, or virtual, limitlessness of supply, which can be defined, albeit arbitrarily, as corresponding to a few million years. The fuels for nuclear fusion - lithium and deuterium - satisfy this condition because of the abundance of lithium in seawater and of deuterium in all forms of water. The possible use of lithium-ion batteries on a large scale, particularly in the automobile industry, could, however, use up all the known terrestrial reserves and resources of lithium in the next few decades. Little attention has been paid so far to the financial, energetic, and above all, environmental aspects of lithium extraction from seawater. The neutron multipliers foreseen for fusion power plants, in particular beryllium, represent a major supply problem and require that other, sustainable solutions be urgently sought.