Uranium nuclear properties

Its importance depends on the nuclear property of being readily fissionable with neutrons and its availability in quantity. The world s nuclear-power reactors are now producing about 20,000 kg of plutonium/yr. By 1982 it was estimated that about 300,000 kg had accumulated. The various nuclear applications of plutonium are well known. 238Pu has been used in the Apollo lunar missions to power seismic and other equipment on the lunar surface. As with neptunium and uranium, plutonium metal can be prepared by reduction of the trifluoride with alkaline-earth metals. 

AH of the 15 plutonium isotopes Hsted in Table 3 are synthetic and radioactive (see Radioisotopes). The lighter isotopes decay mainly by K-electron capture, thereby forming neptunium isotopes. With the exception of mass numbers 237 [15411-93-5] 241 [14119-32-5] and 243, the nine intermediate isotopes, ie, 236—244, are transformed into uranium isotopes by a-decay. The heaviest plutonium isotopes tend to undergo P-decay, thereby forming americium. Detailed reviews of the nuclear properties have been pubUshed (18). 

The recognition in 1940 that deuterium as heavy water [7789-20-0] has nuclear properties that make it a highly desirable moderator and coolant for nuclear reactors (qv) (8,9) fueled by uranium (qv) of natural isotopic composition stimulated the development of industrial processes for the manufacture of heavy water. Between 1940 and 1945 four heavy water production plants were operated by the United States Government, one in Canada at Trail,... 

The element was discovered in the pitchblende ores by the German chemist M.S. Klaproth in 1789. He named this new element uranium after the planet Uranus which had just been discovered eight years earlier in 1781. The metal was isolated first in 1841 by Pehgot by reducing the anhydrous chloride with potassium. Its radioactivity was discovered by Henry Becquerel in 1896. Then in the 1930 s and 40 s there were several revolutionary discoveries of nuclear properties of uranium. In 1934, Enrico Fermi and co-workers observed the beta radioactivity of uranium, following neutron bombardment and in 1939, Lise Meitner, Otto Hahn, and Fritz Strassmann discovered fission of uranium nucleus when bombarded with thermal neutrons to produce radioactive iso-... 

Hoekstra, H. R., ed., Uranium Dioxide, Properties and Nuclear Applications, Phase Relationships in Uranium-Oxygen and Binary Oxide Systems, Chap. 6, p. 251, U. S. Atomic Energy Commission, 1961. 

Not every actinide element has known or well-developed organometallic chemistry. By far the most research has been done on thorium and uranium compounds, a consequence of favorable isotope-specific nuclear properties and, at least until recently, the commercial availability of key starting materials such as Th metal, anhydrous ThCLi, U metal, and anhydrous UCL. Thorium chemistry is dominated by the -F4 oxidation state and has some similarities to the chemistry of the heavier group 4 metals. For uranium, one can access oxidation states from d-3 to 4-6 in organic media. Although there are some similarities to the chemistry of the heavier group 6 elements, for example, tungsten, there are also some remarkable differences made possible by the availability of the 5f valence orbitals. 

The majority of the longer-lived transuranic nuclides produced by neutron capture reactions decay primarily by a-emission. Most environmental samples contain radionuclides from the natural uranium and thorium series in concentrations often many times greater than transuranic concentrations. As a result, the chemical problems encountered in these measurements are derived from the requirement that separated trans-uranics should be free of a-emitting natural-series nuclides which would constitute a-spectrometric interferences. Table I lists those transuranic nuclides detected to date in marine environmental samples, together with some relevant nuclear properties. Their relative concentrations (on an activity basis) are indicated although the ratios may be altered by environmental fractionation processes which enrich and deplete the relative concentrations of the various transuranic elements. Alpha spectrometric measurements do not distinguish between 239p Pu, so these are... 

Nuclear properties of Pu become more favorable for breeding if fission is carried out with fast neutrons, with kinetic energies of the order of 2 X 10 eV. In such a fast reactor the TJ for plutonium is around 2.3, and breeding with U (or natural uranium) is possible. 

Table S.l lists the isotopes of uranium that are important in nuclear technology and their most important nuclear properties.

Table 9.13 lists the isotopes of plutonium important in nuclear technology and some of their important nuclear properties. Plutonium isotopes are produced in reactors by the nuclide chains shown in Fig. 8.5. Typical quantities and isotopic compositions of plutonium in various reactor fuel cycles are listed in Tables 8.4, 8.5,8.6, and 8.7. In reactors fueled with uranium and plutonium, Pu is the principal isotopic constituent, but Pu contributes the greatest amount of alpha activity. With U-thorium fueling, Pu is the principal isotopic constituent. 

The first transuranium elements, neptunium and plutonium, were obtained in tracer amounts from bombardments of uranium by McMillan and Abelson and by Seaborg, McMillan, Kennedy, and Wahl, respectively, in 1940. Both elements are obtained in substantial quantities from the uranium fuel elements of nuclear reactors. Only plutonium is normally recovered and is used as a nuclear fuel since, like 235U, it undergoes fission its nuclear properties apparently preclude its use in hydrogen bombs. Certain isotopes of the heavier elements are made by successive neutron capture in 239Pu in high-flux nuclear reactors (> 1015 neutrons cm-2 sec- ). Others are made by the action of accelerated heavy ions of B, C, N, O or Ne on Pu, Am or Cm. 

Not every actinide element has known or well-developed organometallic chemistry. By far the most research has been done on thorium and uranium compounds, a consequence of favorable isotope-specific nuclear properties and, at least until recently, the commercial availability of key starting materials such as Th metal, anhydrous ThCH, U metal, and anhydrous Thorium chemistry is dominated... 

The sole reason for using thorium in nuclear reactors is the fact that thorium ( Th) is not fissile, but can be converted to uranium-233 (fissile) via neutron capture. Uranium-233 is an isotope of uranium that does not occur in nature. When a thermal neutron is absorbed by this isotope, the number of neutrons produced is sufficiently larger than two, which permits breeding in a thermal nuclear reactor. No other fuel can be used for thermal breeding applications. It has the superior nuclear properties of the thorium fuel cycle when applied in thermal reactors that motivated the development of thorium-based fuels. The development of the uranium fuel cycle preceded that of thorium because of the natural occurrence of a fissile isotope in natural uranium, uranium-235, which was capable of sustaining a nuclear chain reaction. Once the utilization of uranium dioxide nuclear fuels had been established, development of the compound thorium dioxide logically followed. 

Different isotopes of an element have different natural abundances. For example, 99.3% of naturally occurring uranium is uranium-238, 0.7% is uranium-235, and only a trace is uranium-234. Different isotopes of an element also have different stabilities. Indeed, the nuclear properties of any given isotope depend on the number of protons and neutrons in its nucleus. 

The breeding ratio values given in the fifth column of 50 Table I are based on the nuclear properties of plutonium and uranium and take into account neutrons lost by leakage from the reactor as well as those neutrons lost by capture in the coolant and in the metallic protective jacket enclosing the fission metal. It is assumed that the 65 coolant has an absorption cross section per cubic centimeter which is about that of natural uranium, and that the absorption cross section per cubic centimeter of the jacket metal is about that of natural uranium. 

Although aluminium and its alloys have attractive nuclear properties, they have limited strength, poor compatibility with uranium at high temperatures and low corrosion resistance in water or steam at temperatures above 523 K. Hence their use is restricted to core components in research reactors, where temperatures do not exceed 423 K. However, various parameters, such as water quality, structural design (crevices, galvanic contact with other materials), alloy composition and irradiation, have significant influence on the corrosion resistance of aluminium in research reactors. 

Isotopes. Forms of the same element having identical chemical properties but differing in their atomic masses (because they have different numbers of neutrons in their respective nuclei) and nuclear properties. For example, hydrogen has three isotopes hydrogen, with a mass of 1 deuterium, with a mass of 2 and tritium, with a mass of 3. The first two are stable (nonradioactive), but tritium is a radioactive isotope. Nuclides have the same number of protons in their nuclei and hence the same atomic number, but differ in the number of neutrons and therefore in mass. Both isotopes of uranium, with masses of 235 and 238 units respectively, are radioactive (emit alpha particles), but their half-lives are different, releasing their radioactivity at a different rate. Furthermore, uranium 235 is readily fissionable by neutrons of all energies, while uranium 238 is not. 

To a very good approximation, different isotopes of the same elanent have identical chemical properties however, they can differ in some physical properties, such as density, which depends on mass, and radioactivity, which depends on the ratio of neutrons to protons in the nucleus, as will be discussed in Chapter 17. Two common isotopes of uranium (Z = 92), for example, have mass numbers 235 and 238. The lighter isotope ( U) is used in nuclear reactors and atomic bombs, whereas ( U) lacks the nuclear properties necessary for these applications. With the exception of hydrogen, which has different names for each of its isotopes, isotopes of elements are identified by their mass numbers. Thus, the two common isotopes of uranium are called uranium-235 and uranium-238. A list of the stable and radioactive isotopes for the first 10 elements is given in Appendix 4. 

A Thorium-Uranium Exponential Experltnenti C. If. Skeen and W. W. Broum(AI). Because of uncertainties in the knowledge of t nuclear properties of thorium fuel and lattices containing this fuel, an experimental study was made of a thorium based fuel that is to be loaded into the Sodium Reactor Experiment (8RB) in the near future. An exponential experiment was performed with a square-celled lattice of 7-rod elements (l-in. diameter rods) spaced 9.5 in. apart in praphite. The fuel Is a Th-U-23S alloy containing 7.6% uranium by weight which is 93.13 atomic per cent U-235. The feel elements were 5 ft. long. The subcrltical lattice was placed On thd thermal column of a water boiler reactor which served as the source of neutrons for the assembly. 

Since Fermi s early work on exponential experiments the design of reactors has depended heavily on the experimental determination of nuclear properties of multiplying assemblies in subcritical Or critical experiments. In thermal assemblies the nuclear properties studied have included macroscopic flux traverses, from which the material buckling can be obtained, and ratios related to quantities which enter into the four-factor formula for k. One ratio measured in uranium fueled assemblies is ... 

We open with a concise introduction on the sources of uranium in nature and its main physical, chemical, and nuclear properties and then briefly discuss the chan-istry of uranium and its compounds with phasis on those that play an important role in uranium processing, namely, in the uranium fuel cycle. As we are concerned with the modem analytical chemistry of uranium, we present the foremost analytical techniques that are used nowadays to characterize uranium in its different forms. 

Highlights The tolerance for impurities and isotopic composition of DU is quite large compared with the very strict specifications for nuclear fuel or for the feed material of enrichment plants (in fact, we did not find such specifications for DU). After dissolution of the DU, the analytical techniques used are basically the same for all forms of uranium. In cases where DU is fabricated from reprocessed fuel, some additional tests are required to verify the radioactivity. One feature of DU is that it is alloyed with different elements in order to improve its physical properties (like hardness or density) without any concerns about the nuclear properties of the alloy. 

The rigorons specifications for nuclear grade materials that are used as nuclear fuel (mainly UO2 and U metal or alloys) or as feed material for enrichment facilities (primarily UFg) are described in great detail and require strict control. The focus of the analytical procedures is on impurities that affect the nuclear properties (mainly through absorption of neutrons), chemical properties (Uke corrosion resistance or those that may concentrate in the enrichment product), and physical and mechanical properties (like pellet strength, heat transfer). The isotopic composition of uranium plays an important role as the value of uranium strongly depends on the content. 

In ordinary chemical reactions the chemical properties of an element depend only on the electrons outside the nucleus, and the properties are essentially the same for all isotopes of the element. The nuclear properties of the various isotopes of an element are quite different, however. In the radioactive decay series beginning with uranium-238, goTh emits a j8-particle, whereas a bit farther down the line loTh ejects an a-particle. Both Ph and g Pb are j8-particle emitters toward the end of the series, while the final product, gfPb, has a stable nucleus, emitting neither alpha nor beta particles nor gamma rays. 

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