Fuel Composition and Long Term Radioactivity
Long-lived radioactive waste from the back end of the fuel cycle is especially relevant when designing a complete waste management plan for SNF. When looking at long-term radioactive decay, the actinides in the SNF have a significant influence due to their characteristically long half-lives. Depending on what a nuclear reactor is fueled with, the actinide composition in the SNF will be different.
An example of this effect is the use of nuclear fuels with thorium. Th-232 is a fertile material that can undergo a neutron capture reaction and two beta minus decays, resulting in the production of fissile U-233. The SNF of a cycle with thorium will contain U-233, an isotope with a half-life of 160,000 years. Its radioactive decay will strongly influence the long-term activity curve of the SNF around 1,000,000 years. A comparison of the activity associated to U-233 for three different SNF types can be seen in the figure on the top right.
The burnt fuels are Thorium with Reactor-Grade Plutonium (RGPu), Thorium with Weapons-Grade Plutonium (WGPu) and Mixed Oxide fuel (MOX). For RGPu and WGPu, the initial amount of U-233 and its decay around 10E5 years can be seen. This has an effect in the total activity curve of the three fuel types. The absence of U-233 and its daughter products in the MOX fuel results in a lower activity in region 3 of the figure on the bottom right, whereas for RGPu and WGPu the curve is maintained higher due to the presence of U-233 that has not fully decayed.
The use of different fuels in nuclear reactors results in different SNF composition, with varying activity curves.
Read more about this topic: Spent Nuclear Fuel
Famous quotes containing the words fuel, composition, long and/or term:
“It is now many years that men have resorted to the forest for fuel and the materials of the arts: the New Englander and the New Hollander, the Parisian and the Celt, the farmer and Robin Hood, Goody Blake and Harry Gill; in most parts of the world, the prince and the peasant, the scholar and the savage, equally require still a few sticks from the forest to warm them and cook their food. Neither could I do without them.”
—Henry David Thoreau (1817–1862)
“When I think of God, when I think of him as existent, and when I believe him to be existent, my idea of him neither increases nor diminishes. But as it is certain there is a great difference betwixt the simple conception of the existence of an object, and the belief of it, and as this difference lies not in the parts or composition of the idea which we conceive; it follows, that it must lie in the manner in which we conceive it.”
—David Hume (1711–1776)
“The statements of science are hearsay, reports from a world outside the world we know. What the poet tells us has long been known to us all, and forgotten. His knowledge is of our world, the world we are both doomed and privileged to live in, and it is a knowledge of ourselves, of the human condition, the human predicament.”
—John Hall Wheelock (1886–1978)
“Dead drunk
is the term I think of,
insensible,
neither cool nor warm,
without a head or a foot.
To be drunk is to be intimate with a fool.”
—Anne Sexton (1928–1974)