Plutonium natural abundance

Low-Level Waste. Low-level wastes are further divided into categories of special nuclear material, source material, and byproduct material, depending on the isotopes contained. Special nuclear material refers to uranium 233, plutonium 239, and uranium containing more than the natural abundance of uranium 235. Source material refers to materials containing 0.05 percent or more of thorium or uranium in any physical or chemical form except that covered under special nuclear material. By-product materials consist of all other radioactive materials including fission and activation products. 

For elements with low natural abundance, it can sometimes be found that the isotope ratio measurement limits the LOD. But even for naturally low abundant elements such as uranium, plutonium, and the PGEs, the corresponding isotope intensities are often subject to interferences by small contributions from polyatomic ions [25, 26]. Such interferences simulate an additional blank value, which is still covered by the blank measurement, at least if the corresponding procedure with the blank solution gives rise to the same polyatomic ions as the real sample. 

A limitation of fission reactors is the fact that only 0.71% of natural uranium is fissionable uranium-235. This situation could be improved by the development of breeder reactors, which convert uranium-238 (natural abundance 99.28%) to fissionable plutonium-239. 

Nuclear reactors can be designed on the basis of their fuel cycle such that they breed more fissile nuclides than what they use. Breeder reactors can utilize uranium, thorium, and plutonium resources more efficiently. There are two types of breeder reactors (1) fast neutron spectmm breeder and (2) thermal neutron spectmm breeder reactors, which are designed based on (99.2% natural abundance) and Th (100% natural abundance), respectively. Fertile nuclides and Th capture neutrons and trans-form, respectively, to fissile nuclides Pu and U. Through this process, which is known as breeding, the reactor produces more fissile nuclides than what it consumes. Fast-breeder reactors (FBRs) can also be used in order to transmute the long-lived... 

Plutonium occurs in natural ores in such small amounts that separation is impractical. The atomic ratio of plutonium to uranium in uranium ores is less than 1 10 however, traces of primordial plutonium-244 have been isolated from the mineral bastnasite (16). One sample contained 1 x 10 g/g ore, corresponding to a plutonium-244 [14119-34-7] Pu, terrestrial abundance of 7 x 10 to 2.8 x 10 g/g of mineral and to <10g of primordial Pu on earth. The content of plutonium-239 [15117 8-3], Pu, in uranium minerals is given in Table 2. 

The most common use of uranium is to convert the rare isotope U-235, which is naturally fissionable, into plutonium through neutron capture. Plutonium, through controlled fission, is used in nuclear reactors to produce energy, heat, and electricity. Breeder reactors convert the more abundant, but nonfissionable, uranium-238 into the more useful and fissionable plutonium-239, which can be used for the generation of electricity in nuclear power plants or to make nuclear weapons. 

The energy output of a nuclear reactor is characterized by the bum-up which is usually given in megawatt-days (MW d) per ton of fuel. By use of natural uranium a burn-up of about 10 MW d per ton is achieved. This corresponds to the fission of about 13 kg of fissile nuclides per ton of fuel, the greatest part being Pu produced by reaction (11.4) The fission of leads to a decrease of its concentration below the natural isotopic abundance of 0.72%. From the economic point of view, only the recovery of plutonium is of interest. 

All isotopes of technetium are unstable toward ft decay or electron capture and traces exist in Nature only as fragments from the spontaneous fission of uranium. The element was named technetium by the discoverers of the first radioisotope—Perrier and Segre. Three isotopes have half-lives greater than 105 years, but the only one that has been obtained on a macro scale is "Tc (fi, 2.12xl05 years). Technetium is recovered from waste fission-product solutions after removal of plutonium and uranium. It is an interesting irony that the supply of technetium, which does not exist in Nature, might easily be made to exceed that of Re, which does, because of the increasing number of reactors and the very low ( 10-9%) abundance of Re in the earth s crust. 

The most important isotope of plutonium is Pu = 24,200 years). It has a short half-life so only ultra traces of plutonium occur naturally in uranium ores, and most plutonium is artificial, being an abundant byproduct of uranium fission in nuclear power reactors. The nuclear reactions involved include the radiative capture of a thermal neutron by uranium, U( , y) U the uranium-239 produced is a beta-emitter that yields the radionuclide Np, also a beta-emitter that yields Pu. To date, 15 isotopes of plutonium are known, taking into account nuclear isomers. The plutonium isotope Pu is an alpha-emitter with a half-life of 87 years. Therefore, it is well suited for electrical power generation for devices that must function without direct maintenance for time scales approximating a human lifetime. It is therefore used in radioisotope thermoelectric generators such as those powering the Galileo and Cassini space probes. 

Uraniuin-235 is capable of sustaining a chain reaction, but it makes up only 0.7% of all naturally occurring uranium. Therefore, it is not a very satisfactory source of nuclear fuel (Fig. 20.16). An alternative is the plutonium isotope, Pu, produced from the most abundant uranium isotope (Equations 20.4 to 20.6). Pu has a long half-life (24,360 years) and is fissionable. It has been used in the production of atomic bombs and is also used in some nuclear power plants to generate electrical energy. It is made in a breeder reactor, the name given to a device whose purpose is to produce fissionable fuel from nonfissionable isotopes. 

True a, d, f, g, j, k. False b, c, e, h, i, m. The answer to 1 is left to you. 61. Natural fissionable isotopes are rare. Plutonium-234 is produced fiom the most abundant uranium isotope, uranium-238. 62. Presumably, it takes an infinite time for all of a sample of radioactive matter to decay. 

The Th U cycle is attractive because it is based on the conversion of the relatively abundant element thorium into an isotope of uranium which has nuclear characteristics superior to those of in a thermal reactor. Since, unlike uranium, thorium in the natural state does not incorporate a thermally fissile isotope, the Th -U cycle has lagged behind that of XJ238 p 239 which was based on the automatic inclusion of the contained in natural uranium. In addition, the radiological problems involved in the handling of highly irradiated thorium are somewhat more severe than those encountered in the plutonium cycle. 

Uranium-238 is the most abundant isotope of uranium, constituting approximately 99.2830 percent of natural uranium. It is not fissionable, but it is a fertile material, forming the fissile isotope plutonium-239 as a result of neutron bombardment. 

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