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:
“Beware the/easy griefs, that fool and fuel nothing./It is too easy to cry “AFRIKA!”/and shock thy street,/and purse thy mouth,/and go home to thy “Gunsmoke,” to/thy “Gilligan’s Island” and the NFL.”
—Gwendolyn Brooks (b. 1917)
“Give a scientist a problem and he will probably provide a solution; historians and sociologists, by contrast, can offer only opinions. Ask a dozen chemists the composition of an organic compound such as methane, and within a short time all twelve will have come up with the same solution of CH4. Ask, however, a dozen economists or sociologists to provide policies to reduce unemployment or the level of crime and twelve widely differing opinions are likely to be offered.”
—Derek Gjertsen, British scientist, author. Science and Philosophy: Past and Present, ch. 3, Penguin (1989)
“I’m in clover now, nor know
Who made honey long ago.”
—Edmund Blunden (1896–1974)
“It’s given new meaning to me of the scientific term black hole.”
—Don Logan, U.S. businessman, president and chief executive of Time Inc. His response when asked how much his company had spent in the last year to develop Pathfinder, Time Inc.’S site on the World Wide Web. Quoted in New York Times, p. D7 (November 13, 1995)