Embedding Materials and Economy for a Deep Underground Reactor

I proposed embedding the high-conversion LWR, studied in the NERI program, about 500-1000 meters deep underground. At such depths, the earth's gravity force passively removes heat using the natural circulation of the reactor coolant; then, even a nuclear-power plant with very tight-lattice fuel assembly can be operated safely. Safety is ensured by embedding the reactor vessel and other components, such as coolant ducts, in casing containers and filling the space between the container and the vessel with embedding material. I describe suitable embedding materials that can be easily removed to allow access to the reactor and coolant components. Finally, I discuss the key economic aspects of building a reactor deep underground. (author)