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Spent nuclear fuel stays a radiation hazard for extended periods of time with half-lifes as high as 24,000 years. For example 10 years after removal from a reactor, the surface dose rate for a typical spent fuel assembly still exceeds 10,000 rem/hour—far greater than the fatal whole-body dose for humans of about 500 rem received all at once.
Caesium-134 is found in spent nuclear fuel but is not produced by nuclear weapon explosions, as it is only formed by neutron capture on stable Cs-133, which is only produced by beta decay of Xe-133 with a half-life of 3 days. Cs-134 has a half-life of 2 years and may be a major source of gamma radiation in the first 20 years after discharge.
The high short-term radioactivity of spent nuclear fuel is primarily from fission products with short half-life.The radioactivity in the fission product mixture is mostly due to short-lived isotopes such as 131 I and 140 Ba, after about four months 141 Ce, 95 Zr/ 95 Nb and 89 Sr constitute the largest contributors, while after about two or three years the largest share is taken by 144 Ce/ 144 ...
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 ...
In nuclear reactors both caesium-137 and strontium-90 are found in locations away from the fuel because they're formed by the beta decay of noble gases (xenon-137, with a 3.8-minute half-life, and krypton-90, with a 32-second half-life) which enable them to be deposited away from the fuel, e.g. on control rods.
It has a half-life of 87.7 years, reasonable energy density, and exceptionally low gamma and neutron radiation levels. Some Russian terrestrial RTGs have used 90 Sr; this isotope has a shorter half-life and a much lower energy density, but is cheaper. Early RTGs, first built in 1958 by the U.S. Atomic Energy Commission, have used 210 Po
Radioactive isotope table "lists ALL radioactive nuclei with a half-life greater than 1000 years", incorporated in the list above. The NUBASE2020 evaluation of nuclear physics properties F.G. Kondev et al. 2021 Chinese Phys. C 45 030001. The PDF of this article lists the half-lives of all known radioactives nuclides.
129 I is one of the seven long-lived fission products that are produced in significant amounts. Its yield is 0.706% per fission of 235 U. [7] Larger proportions of other iodine isotopes such as 131 I are produced, but because these all have short half-lives, iodine in cooled spent nuclear fuel consists of about 5/6 129 I and 1/6 the only stable iodine isotope, 127 I.