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Aminor actinide is anactinide, other thanuranium orplutonium, found inspent nuclear fuel. The minor actinides includeneptunium (element 93),americium (element 95),curium (element 96),berkelium (element 97),californium (element 98),einsteinium (element 99), andfermium (element 100).[2] The most important isotopes of these elements inspent nuclear fuel areneptunium-237,americium-241,americium-243,curium-242 through -248, andcalifornium-249 through -252.
Plutonium and the minoractinides will be responsible for the bulk of theradiotoxicity and heat generation ofspent nuclear fuel in the long term (300 to 20,000 years in thefuture).[3]
The plutonium from a power reactor tends to have a greater amount ofplutonium-241 than the plutonium generated by the lowerburnup operations designed to createweapons-grade plutonium. Because thereactor-grade plutonium contains so much241Pu, the presence of241Am makes the plutonium less suitable for making anuclear weapon. The ingrowth of americium in plutonium is one of the methods for identifying the origin of an unknown sample of plutonium and the time since it was last separated chemically from the americium.
Americium is commonly used in industry as both analpha particle source and as a lowphoton-energygamma radiation source. For example, it is commonly used insmoke detectors. Americium can be formed by neutron capture of239Pu and240Pu, forming241Pu which then beta decays to241Am.[4] In general, as the energy of the neutrons increases, the ratio of the fission cross section to the neutron capture cross section changes in favour offission. Hence, ifMOX is used in athermal reactor such as aboiling water reactor (BWR) orpressurized water reactor (PWR) then more americium can be expected to be found in the spent fuel than in that from afast neutron reactor.[5]
Some of the minor actinides have been found infallout from bomb tests. SeeActinides in the environment for details.
| Isotope | Fraction | DLWR | Dfast | Dsuperthermal |
|---|---|---|---|---|
| 237 Np | 0.0539 | 1.12 | −0.59 | −0.46 |
| 238 Pu | 0.0364 | 0.17 | −1.36 | −0.13 |
| 239 Pu | 0.451 | −0.67 | −1.46 | −1.07 |
| 240 Pu | 0.206 | 0.44 | −0.96 | 0.14 |
| 241 Pu | 0.121 | −0.56 | −1.24 | −0.86 |
| 242 Pu | 0.0813 | 1.76 | −0.44 | 1.12 |
| 241 Am | 0.0242 | 1.12 | −0.62 | −0.54 |
| 242m Am | 0.000088 | 0.15 | −1.36 | −1.53 |
| 243 Am | 0.0179 | 0.82 | −0.60 | 0.21 |
| 243 Cm | 0.00011 | −1.90 | −2.13 | −1.63 |
| 244 Cm | 0.00765 | −0.15 | −1.39 | −0.48 |
| 245 Cm | 0.000638 | −1.48 | −2.51 | −1.37 |
| Weighted sum | −0.03 | −1.16 | −0.51 | |
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