Nuclear Waste - graph of fission products.

Capt'n Midnight

In Nuclear Fission the atom splits into two parts (sometimes more). The total mass of these are the original atom plus the colliding neutron. There are over 60 different fission products. But in general for U235one part will be about 96 amu the other 139 amu. Most of these are toxic heavy metals. Many are radioactive and further decay to yet more isotopes. Some have short lives so this happens in the reactor then some waste products have high absorption cross sections for neutrons and so you get yet more isotopes.

It's this witches brew that makes nuclear waste such a problem. You aren't dealing with a few elements that you can isolate chemically, you are dealing with dozens, many of which are so similar chemically that it is difficult to separate them by half life or toxicity.


%;s of fission yield products for thermal neutrons


each dot may represent different isotopes with the same weight, most dots represent a slightly different waste disposal problem

Curves for Uranium 233 and Plutonium 239 are similar but shifted up / down slightly.


For Fusion http://en.wikipedia.org/wiki/Fusion_power

There is also no risk of a runaway reaction in a fusion reactor, since the plasma is normally burnt at optimal conditions, and any significant change will render it unable to produce excess heat.
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the total amount of fusion fuel in the vessel is very small, typically a few grams. If the fuel supply is closed, the reaction stops within seconds.
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Most reactor designs rely on the use of liquid lithium as both a coolant and a method for converting stray neutrons from the reaction into tritium, which is fed back into the reactor as fuel. Lithium is highly flammable, and in the case of a fire it is possible that the lithium stored on-site could be burned up and escape. In this case the tritium contents of the lithium would be released into the atmosphere, posing a radiation risk. However, calculations suggest that the total amount of tritium and other radioactive gases in a typical power plant would be so small, about 1 kg, that they would have diluted to legally acceptable limits by the time they blew as far as the plant's perimeter fence.

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The half-life of the radioisotopes produced by fusion tend to be less than those from fission, so that the inventory decreases more rapidly. Furthermore, there are fewer unique species, and they tend to be non-volatile and biologically less active. Unlike fission reactors, whose waste remains dangerous for thousands of years, most of the radioactive material in a fusion reactor would be the reactor core itself, which would be dangerous for about 50 years, and low-level waste another 100. By 300 years the material would have the same radioactivity as coal ash.
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In general terms, fusion reactors would create far less radioactive material than a fission reactor, the material it would create is less damaging biologically, and the radioactivity "burns off" within a time period that is well within existing engineering capabilities.