• The radioactive products are concentrated in the used or “ spent ” fuel rods. • The fuel rods are referred to as high-level nuclear waste . • The half-lives of several of the products are very long, requiring special storage or disposal. • Spent fuel rods can be reprocessed into new fuel rods. • Reprocessing is not carried out in the United States due to regulatory concerns and nuclear nonproliferation treaties. • All high-level waste is currently stored on-site at the reactor. • On-site storage is not a long term solution.
54 Nuclear Waste • Yucca Mountain, in southwest Nevada, was proposed as the site for an extensive feasibility study for long term storage of high-level waste because it fulfills several general engineering considerations. • Yucca Mountain is extremely remote, the climate is dry, and the water level is about 1000 feet below the potential burial vault. • The storage facility must be remain intact for thousands of years. • The construction materials will need to withstand the effects of high levels of radiation.
55 Fusion • In the sun, four hydrogen nuclei combine to form a helium nucleus, releasing energy in the process. • The reaction of 4 protons is a stepwise process, too slow to be used in a nuclear reactor. • The two heavier isotopes of hydrogen, deuterium ( 2 H) and tritium ( 3 H) can be fused to produce helium • The reaction produces more energy per nucleus than fission. 4 1 1 H 2 4 He + 2 1 0 + 2 + energy 1 2 H + 1 3 H 2 4 He + 0 1 n
56 Fusion • Deuterium is naturally occurring; it makes up 0.015% of all hydrogen atoms. • The available supply of deuterium is practically unlimited. • Tritium can be produced from 6 Li. • Fusion does not produce high-level radioactive waste. • Energetic neutrons can induce nuclear reactions in reactor materials, producing some level of radioactivity. • Risk minimized by careful choices of engineering materials. 3 6 Li + 0 1 n 2 4 He + 1 3 H
57 Fusion • During fusion, the repulsion of positively charged nuclei must be overcome. • Fusion reactions initiated at temperatures on the order of 10 6 K. • High temperature required to force nuclei close enough to overcome coulombic repulsion. • The first application of fusion was the hydrogen bomb . • A fission bomb initiated the fusion reaction. • Controlled fusion must use a nondestructive means of initiation. • As an energy source, fusion must release more energy than it requires as input.
58 Fusion • The fusion reaction must be confined somehow. • Solid reactor materials would melt at the high initiation temperatures. • Two promising means for solving the confinement problem. • Magnetic confinement : The high-energy plasma produced at 10 6 K is controlled in a magnetic field. • Inertial confinement : A pellet of fuel is dropped into a reaction chamber and imploded by high-energy lasers. • So far, more energy is required to produce fusion than is released.
59 Interaction of Radiation and Matter • There are three factors governing the effects of radiation on matter.