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Nuclear Energy
Published in Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff, Radiation and Radioactivity on Earth and Beyond, 2020
Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff
Uranium dioxide, manufactured as ceramic pellets, is used as fuel in most nuclear power reactors. The advantages of ceramics over metal are that they undergo fewer dimensional changes at high temperatures; further, they are less easily damaged by radiation, are chemically more inert, and are effective in retaining the gaseous fission products.
Heat Removal from Nuclear Fuel Rods
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
The volumetric heat generation rate q‴ is a function of the amount of fuel a fuel assembly contains, and generally speaking, the more U-235 or Pu-239 that is present (or the higher the enrichment of the fuel), the higher the volumetric heat generation rate will be. Normally, U-235 and U-238 atoms are combined with two oxygen atoms to form a compound called uranium dioxide (or UO2). UO2 is a complex ceramic material with a very high melting point (about 2,800°C), and in some cases, it can withstand similar temperatures to the heat tiles that are used on the U.S. Space Shuttle (see Chapter 10). Sometimes plutonium dioxide PuO2 (a by-product of the fission process) is also mixed with uranium dioxide to form what is called metal oxide (or MOX fuel). The melting point of PuO2 is about 2,400°C, and its mechanical properties are very similar to those of UO2. A considerable amount of heat can be generated by even a single nuclear fuel rod, and volumetric power densities as high as q‴ = 110 kilowatts per liter (kW/L) are common in modern PWRs. On the other hand, liquid metal fast breeder reactors (LMFBRs) can have even higher power densities (in the range of q‴ = 300 kW/L – 500 kW/L), and so metallic coolants (such as liquid sodium and liquid mercury) are used to cool them because they are more efficient at removing this additional heat. Using the heat conduction equation we can then predict the shape of the temperature profile T(x, y, z) in a nuclear fuel rod if the value of q′′′(x, y, z) is known.
Modular Nuclear Reactors
Published in Yatish T. Shah, Modular Systems for Energy and Fuel Recovery and Conversion, 2019
The PBMR has a vertical steel reactor pressure vessel which contains and supports a metallic core barrel, which in turn supports the cylindrical pebble fuel core. This core is surrounded on the side by an outer graphite reflector and on top and bottom by graphite structures which provide similar upper and lower neutron reflection functions. Vertical borings in the side reflector are provided for the reactivity control elements. Some 360,000 fuel pebbles (silicon carbide-coated 9.6% enriched uranium dioxide particles encased in graphite spheres of 60 mm diameter) cycle through the reactor continuously (about six times each) until they are expended after about 3 years. This means that a reactor would require 12 total fuel loads in its design lifetime [1,9,10,15,39–41].
Generation of the Thermal Scattering Law of Uranium Dioxide with Ab Initio Lattice Dynamics to Capture Crystal Binding Effects on Neutron Interactions
Published in Nuclear Science and Engineering, 2021
J. L. Wormald, N. C. Fleming, A. I. Hawari, M. L. Zerkle
Uranium dioxide (UO2) is the primary fuel compound used in commercial nuclear power plants. In fission systems, such as nuclear power reactors or spent fuel pools, criticality is dependent on the fission and neutron absorption rates, which are sensitive to the neutron spectrum. At sufficiently low energies, crystal binding influences the neutron cross section, which is an effect that is captured in the thermal scattering law (TSL), , also known as the dynamic structure factor. TSLs are widely used to capture the effects of crystal binding on thermal neutron scattering in criticality analysis; however, these effects may also impact the neutron resonance line shape in the epithermal energy range.1–5 Within the past decade there has been a renewed interest for quantifying the impact of crystal binding on neutron resonance reactions.6–8 Analysis of neutron transmission measurements in 238U (Refs. 9 and 10) has indicated an impact of atomic vibration in UO2 on the Doppler broadening of uranium epithermal resonances at and below room temperature.6,8
Leaching behavior of gamma-emitting fission products, calcium, and uranium from simulated MCCI debris in water
Published in Journal of Nuclear Science and Technology, 2019
Takayuki Sasaki, Shunichi Sakamoto, Daisuke Akiyama, Akira Kirishima, Taishi Kobayashi, Nobuaki Sato
The molar ratio of U:Zr in UO2–ZrO2 sample was assumed to be 5:1, as a result of the combination of UO2 fuel and zircaloy clad. Uranium dioxide powder was obtained by reducing U3O8 powder using Ar with 10% H2 gas at 1273 K for 4 h. The weighed amounts of UO2 and ZrO2 powders and cement were mixed using an agate mortar and pestle for 20 min. After the treatment, the sample was heated in a reaction tube at 1473 K (ca. 13 K/min) for 2 h in a reducing (Ar + 10% H2) or oxidizing (Ar + 2% O2) atmosphere, and, during furnace cooling, a flow of 10% H2 or pure argon gases, respectively, was maintained.
Interesting magnetic response of the nuclear fuel material UO2
Published in Phase Transitions, 2022
Sudip Pal, L. S. Sharath Chandra, Maulindu Kumar Chattopadhyay, S. B. Roy
Uranium dioxide (UO) is a well-known nuclear fuel material and is used worldwide in nuclear reactors for electrical power generation and research. UO is also recognized as a Mott–Hubbard insulator [1, 2], and it promises other technological applications apart from a nuclear fuel [3, 4]. Thermal conductivity is very important for the removal of heat produced in a nuclear reactor by fission in the nuclear fuel materials. As a result thermal properties of UO particularly have drawn much attention over the years [1, 5–8]. UO crystallizes in face centered cubic (fcc) calcium fluorite structure (), in which U ions are surrounded by eight O ions forming a cube [9]. Therefore, the anisotropic thermal conductivity reported in this compound is rather unexpected and emphasizes the relevance of spin-phonon coupling, which is associated with the magnetic state of the system [8]. The Mott insulating state in UO further highlights the importance of strong electron–electron correlation in the system [2, 4]. Various techniques, including neutron scattering and nuclear magnetic resonance (NMR) have revealed a complex 3k-non-collinear antiferromagnetic (AFM) spin ordering below K. The transition is first order in nature and is accompanied by a small lattice distortion, predominantly in the oxygen cage [10–12]. In cubic crystal field, the nine-fold degenerate (, J=4) state splits up with a 3-fold degenerate ground state, resulting in Jahn–Teller (JT) instability [13].