Chemistry:Minor actinide

Short description: Category of elements in spent nuclear fuel

Transmutation flow between ²³⁸Pu and ²⁴⁴Cm in LWR.
Fission percentage is 100 minus shown percentages.
Total rate of transmutation varies greatly by nuclide.
²⁴⁵Cm–²⁴⁸Cm are long-lived with negligible decay.

Minor actinides in the periodic table Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson

Major actinides in the periodic table Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson

A minor actinide is an actinide, other than uranium or plutonium, found in spent nuclear fuel. The minor actinides include neptunium (element 93), americium (element 95), curium (element 96), berkelium (element 97), californium (element 98), einsteinium (element 99), and fermium (element 100). The most important isotopes of these elements in spent nuclear fuel are neptunium-237, americium-241, americium-243, curium-242 through -248, and californium-249 through -252.

Plutonium and the minor actinides will be responsible for the bulk of the radiotoxicity and heat generation of spent nuclear fuel in the long term (300 to 20,000 years in the future).

The plutonium from a power reactor tends to have a greater amount of plutonium-241 than the plutonium generated by the lower burnup operations designed to create weapons-grade plutonium. Because the reactor-grade plutonium contains so much ²⁴¹Pu, the presence of ²⁴¹Am makes the plutonium less suitable for making a nuclear 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 an alpha particle source and as a low photon-energy gamma radiation source. For example, it is commonly used in smoke detectors. Americium can be formed by neutron capture of ²³⁹Pu and ²⁴⁰Pu, forming ²⁴¹Pu which then beta decays to ²⁴¹Am. 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 of fission. Hence, if MOX is used in a thermal reactor such as a boiling water reactor (BWR) or pressurized water reactor (PWR) then more americium can be expected to be found in the spent fuel than in that from a fast neutron reactor.

Some of the minor actinides have been found in fallout from bomb tests. See Actinides in the environment for details.

Transuranics in LWR spent fuel (burnup 55 GWd_th/T) and mean neutron consumption via fission

Negative numbers mean net neutron producer

Isotope	Fraction	DLWR	Dfast	Dsuperthermal
237Np	0.0539	1.12	−0.59	−0.46
238Pu	0.0364	0.17	−1.36	−0.13
239Pu	0.451	−0.67	−1.46	−1.07
240Pu	0.206	0.44	−0.96	0.14
241Pu	0.121	−0.56	−1.24	−0.86
242Pu	0.0813	1.76	−0.44	1.12
241Am	0.0242	1.12	−0.62	−0.54
242mAm	0.000088	0.15	−1.36	−1.53
243Am	0.0179	0.82	−0.60	0.21
243Cm	0.00011	−1.90	−2.13	−1.63
244Cm	0.00765	−0.15	−1.39	−0.48
245Cm	0.000638	−1.48	−2.51	−1.37
Weighted sum		−0.03	−1.16	−0.51