Uranium-238
Decay mode Decay energy (MeV) | | |
| alpha decay | 4.267 | |
|---|---|---|
| Isotopes of uranium Complete table of nuclides | ||
Uranium-238 (238U or U-238) is the most common
Around 99.284% of natural uranium's mass is uranium-238, which has a half-life of 1.41×1017 seconds (4.468×109 years, or 4.468 billion years).[1] Due to its natural abundance and half-life relative to other
Nuclear energy applications
In a fission
Pu that it cannot be used in current reactors operating with a thermal neutron spectrum. The latter usually involves used "recycled" MOX fuel which entered the reactor containing significant amounts of plutonium[citation needed
Breeder reactors
238U can produce energy via
238U can be used as a source material for creating plutonium-239, which can in turn be used as nuclear fuel. Breeder reactors carry out such a process of transmutation to convert the fertile isotope 238U into fissile 239Pu. It has been estimated that there is anywhere from 10,000 to five billion years worth of 238U for use in these power plants.[7] Breeder technology has been used in several experimental nuclear reactors.[8]
By December 2005, the only breeder reactor producing power was the 600-megawatt BN-600 reactor at the Beloyarsk Nuclear Power Station in Russia. Russia later built another unit, BN-800, at the Beloyarsk Nuclear Power Station which became fully operational in November 2016. Also, Japan's Monju breeder reactor, which has been inoperative for most of the time since it was originally built in 1986, was ordered for decommissioning in 2016, after safety and design hazards were uncovered, with a completion date set for 2047. Both China and India have announced plans to build nuclear breeder reactors.[citation needed]
The breeder reactor as its name implies creates even larger quantities of 239Pu or 233U than the fission nuclear reactor.[citation needed]
The
CANDU reactors
Natural uranium, with 0.7% 235
U
, is usable as nuclear fuel in reactors designed specifically to make use of naturally occurring uranium, such as CANDU reactors. By making use of non-enriched uranium, such reactor designs give a nation access to nuclear power for the purpose of electricity production without necessitating the development of fuel enrichment capabilities, which are often seen as a prelude to weapons production[citation needed].
Radiation shielding
238U is also used as a
Downblending
The opposite of enriching is
238U from depleted uranium and natural uranium is also used with recycled 239Pu from nuclear weapons stockpiles for making
Nuclear weapons
 | This section needs additional citations for verification. (December 2022) |
Most modern
The larger portion of the total explosive yield in this design comes from the final fission stage fueled by 238U, producing enormous amounts of radioactive
Radium series (or uranium series)
The
![{\displaystyle {\begin{array}{l}{}\\{\ce {^{238}_{92}U->[\alpha ][4.468\times 10^{9}\ {\ce {y}}]{^{234}_{90}Th}->[\beta ^{-}][24.1\ {\ce {d}}]{^{234\!m}_{91}Pa}}}{\begin{Bmatrix}{\ce {->[0.16\%][1.17\ {\ce {min}}]{^{234}_{91}Pa}->[\beta ^{-}][6.7\ {\ce {h}}]}}\\{\ce {->[99.84\%\ \beta ^{-}][1.17\ {\ce {min}}]}}\end{Bmatrix}}{\ce {^{234}_{92}U->[\alpha ][2.445\times 10^{5}\ {\ce {y}}]{^{230}_{90}Th}->[\alpha ][7.5\times 10^{4}\ {\ce {y}}]{^{226}_{88}Ra}->[\alpha ][1600\ {\ce {y}}]{^{222}_{86}Rn}}}\\{\ce {^{222}_{86}Rn->[\alpha ][3.8235\ {\ce {d}}]{^{218}_{84}Po}->[\alpha ][3.05\ {\ce {min}}]{^{214}_{82}Pb}->[\beta ^{-}][26.8\ {\ce {min}}]{^{214}_{83}Bi}->[\beta ^{-}][19.9\ {\ce {min}}]{^{214}_{84}Po}->[\alpha ][164.3\ \mu {\ce {s}}]{^{210}_{82}Pb}->[\beta ^{-}][22.26\ {\ce {y}}]{^{210}_{83}Bi}->[\beta ^{-}][5.012\ {\ce {d}}]{^{210}_{84}Po}->[\alpha ][138.38\ {\ce {d}}]{^{206}_{82}Pb}}}\end{array}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/857268db1d49629548dd8bac3ed5d0721553c6d8)
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The
Thorium-234 has a mean lifetime of 3×106 seconds, so there is equilibrium if one mole of 238U contains 9×1012 atoms of thorium-234, which is 1.5×10−11 mole (the ratio of the two half-lives). Similarly, in an equilibrium in a closed system the amount of each decay product, except the end product lead, is proportional to its half-life.
While 238U is minimally radioactive, its decay products, thorium-234 and protactinium-234, are beta particle emitters with half-lives of about 20 days and one minute respectively. Protactinium-234 decays to uranium-234, which has a half-life of hundreds of millennia, and this isotope does not reach an equilibrium concentration for a very long time. When the two first isotopes in the decay chain reach their relatively small equilibrium concentrations, a sample of initially pure 238U will emit three times the radiation due to 238U itself, and most of this radiation is beta particles.
As already touched upon above, when starting with pure 238U, within a human timescale the equilibrium applies for the first three steps in the decay chain only. Thus, for one mole of 238U, 3×106 times per second one alpha and two beta particles and a gamma ray are produced, together 6.7 MeV, a rate of 3 µW.[10][11]
238U atom is itself a gamma emitter at 49.55 keV with probability 0.084%, but that is a very weak gamma line, so activity is measured through its daughter nuclides in its decay series.[12][13]
Radioactive dating
238U abundance and its decay to daughter isotopes comprises multiple uranium dating techniques and is one of the most common radioactive isotopes used in radiometric dating. The most common dating method is uranium-lead dating, which is used to date rocks older than 1 million years old and has provided ages for the oldest rocks on Earth at 4.4 billion years old.[14]
The relation between 238U and 234U gives an indication of the age of sediments and seawater that are between 100,000 years and 1,200,000 years in age.[15]
The 238U daughter product, 206Pb, is an integral part of
The
Health concerns
Uranium emits alpha particles through the process of alpha decay. External exposure has limited effect. Significant internal exposure to tiny particles of uranium or its decay products, such as thorium-230, radium-226 and radon-222, can cause severe health effects, such as cancer of the bone or liver.
Uranium is also a toxic chemical, meaning that ingestion of uranium can cause kidney damage from its chemical properties much sooner than its radioactive properties would cause cancers of the bone or liver.[18][19]
See also
References
- ^ Mcclain, D. E.; Miller, A. C.; Kalinich, J. F. (December 20, 2007). "Status of Health Concerns about Military Use of Depleted Uranium and Surrogate Metals in Armor-Penetrating Munitions" (PDF). NATO. Archived from the original (PDF) on April 19, 2011. Retrieved November 14, 2010.
- .
- S2CID 4367737.
- ^ Nuclear France: Materials and sites. "Uranium from reprocessing". Archived from the original on October 19, 2007. Retrieved March 27, 2013.
- ^ "Plutonium - World Nuclear Association".
- ^ "Physics of Uranium and Nuclear Energy". World Nuclear Association. Retrieved November 17, 2017.
- ^ Facts from Cohen Archived 2007-04-10 at the Wayback Machine. Formal.stanford.edu (2007-01-26). Retrieved on 2010-10-24.
- ^ Advanced Nuclear Power Reactors | Generation III+ Nuclear Reactors Archived June 15, 2010, at the Wayback Machine. World-nuclear.org. Retrieved on 2010-10-24.
- LCCN 2016935977.
- OSTI 1525592.
- ^ "5.3: Types of Radiation". Chemistry LibreTexts. July 26, 2017. Retrieved May 16, 2023.
- ISSN 0969-8043.
- ^ Clark, DeLynn (December 1996). "U235: A Gamma Ray Analysis Code for Uranium Isotopic Determination" (PDF). Retrieved May 21, 2023.
- ISSN 0003-004X.
- .
- .
- ^ "Voyager - Making of the Golden Record". voyager.jpl.nasa.gov. Retrieved March 28, 2020.
- ^ Radioisotope Brief CDC (accessed November 8, 2021)
- ^ Uranium Mining in Virginia: Scientific, Technical, Environmental, Human Health and Safety, and Regulatory Aspects of Uranium Mining and Processing in Virginia, Ch. 5. Potential Human Health Effects of Uranium Mining, Processing, and Reclamation. National Academies Press (US); December 19, 2011.
External links