Frank Shu speaks on the Astrophysics of Thorium Molten-salt Breeder Reactors

Many experts believe that a solution for climate change, especially in nations that are still trying to develop their economies, is not possible without nuclear power. However, among the general public there is discomfort about the four S’s:
• Sustainability (including the problem of the disposal of nuclear waste)
• Security (against the increase of nuclear weapons in the world)
• Superiority (cost for electricity generation relative to coal or natural gas)
• Safety (eliminate the danger of large-scale release of radioactivity)
Under the leadership of its top nuclear scientists, India has a far-sighted program to address these concerns by switching from the current fuel cycle of light-water reactors burning uranium-235 to an alternative fuel cycle that would burn uranium-233 bred from thorium-232 (the only form of thorium found in the world, and for which India has rich deposits). From the perspective of theoretical astrophysics, Prof. Shu argued that the best reactor to achieve the four-S goal uses, not solid fuel elements, but liquid fuel elements in the form of molten salts. Knowledge of how specific isotopes are produced in the big bang, in advanced stages of stellar evolution, and in cosmic rays, help in the choice of the composition of the salts and the materials used in the construction of molten-salt breeder reactors (MSBRs). The exchange of the kinetic energies of neutrons and atomic nuclei in a spherical reactor is akin to similar interactions among low-mass and high-mass stars in a globular cluster, the basic equations for which were formulated by S. Chandrasekhar in the 1940s. Tailoring the nuclear reactions to favour the formation of certain isotopes versus competitors has an analogy with the s- and r-processes of neutron-capture transformations in pre-supernova stars. Achieving economic superiority relative to other sources of energies relies on a basic understanding of energy hierarchies in the natural world. Managing the decay heat in fuel salt dumped into metal tanks in severe emergencies benefits from knowing how white dwarf stars cool by stages to a final inert state as a solid. If the world adopts sustainable, secure, superior, and safe thorium-MSBRs as the primary clean replacement for coal and natural gas, halting climate change could be a solved problem by the end of the twenty-first century without destroying the aspirations of future generations for a better life.