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Fast Reactors, Gas Reactors, and Military Reactors
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
LMFBR cores are similar to each other in pool-type and loop-type designs. In general, they have very high power densities (on the order of 300 kW/L), and because they do not require a moderator, the fuel rods can be placed very closely together. The fuel assemblies are hexagonal in shape, and depleted uranium or U-238 is used as the fertile material (to breed more Plutonium-239). The fissile material is normally a mixture of U-235 and Pu-239. However, pure plutonium dioxide (PuO2) can also be used. The standard enrichment or the standard Pu-239 concentration varies between 16% and 20%. The fuel pellets are stacked in stainless steel tubes, and the fuel pellets are even smaller than those used in a PWR (because of the higher power densities). In the Superphenix, the fuel pellets have a diameter of 7.14 mm. The fuel rods have an outer diameter of 8.5 mm, and the active length of the fuel rods in the core is 2.7 m. In the radial blanket, the fuel rods have a diameter of 15.8 mm (because they are primarily depleted uranium), and the active fuel length is 1.94 m. Hence, the core is relatively compact by water reactor standards. The rod pitch is 9.8 mm in the core and 17.0 mm in the radial blanket.
Cooling during Fuel Removal and Processing
Published in Geoffrey F. Hewitt, John G. Collier, Introduction to Nuclear Power, 2018
Geoffrey F. Hewitt, John G. Collier
In a nuclear reactor, the fissile material is gradually used up and converted to energy and fission products. During the nuclear reaction there are changes in the microstructure of the fuel due to the release of fission products, which either combine with the fuel or are released inside the fuel can. These changes have two effects: (1) a gradual deformation of the fuel and in some cases the can and (2) the release of fission products (such as xenon and iodine), which are themselves strong absorbers of neutrons, leading to a reduction in neutron population and a less efficient nuclear reaction. For these reasons, the fuel element must be removed from the reactor after a period of time and before all the fissile material is used up. Typically this period will be between 3 and 5 years for thermal reactors and 1 year to 18 months for fast reactors. For thermal reactors, 60 to 75% of the original fissile material is used up at the time of fuel removal. For the fast reactor, the utilization is much less, of the order of 25%. The fraction utilized is often referred to as the burn-up.
F
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
where Y is a N -dimensional vector indexed by a vector of parameters . See also Cramer-Rao bound. fissile material an isotope which has a significant probabilitty of undergoing nuclear fission, e.g., U235, plutonium-239, thorium-232, and enriched uranium. fission the nuclear reaction in which a single heavy nucleus is split into two or more lighter nucleii called "daughter" products and emit highly energetic sub-atomic particles plus energy in the process. fixed channel assignment (FCA) a technique of assigning radio channels in a communications system in a fixed and predetermined way in accordance with predicted rather than actual interference and propagation conditions. Such assignments are not changed during radio transmission.
Evaluation of Discharged Fuel in Preproposed Breed-and-Burn Reactors from Proliferation, Decay Heat, and Radiotoxicity Aspects
Published in Nuclear Science and Engineering, 2020
Kazuki Kuwagaki, Jun Nishiyama, Toru Obara
Breed-and-burn (B&B) reactors are a special type of fast reactor. In such reactors, neutrons are provided to feed fuel consisting of natural or depleted uranium (fertile material), thus breeding fissile material. After a sufficient breeding level is achieved, the fuel can provide neutrons to the newly loaded feed fuel. Perpetuation of this breeding and neutron-providing process makes it possible to operate a B&B core with only a natural or depleted uranium feed fuel, except for the external fissile source required at initial startup.
Multi-Output Gaussian Processes for Inverse Uncertainty Quantification in Neutron Noise Analysis
Published in Nuclear Science and Engineering, 2023
Paul Lartaud, Philippe Humbert, and Josselin Garnier
In a fissile material, one neutron can induce a fission, leading to the birth of more neutrons and so on. This process creates correlations between the neutrons. The successive fissions can be described as branching processes, where each fission event is a node in a fission chain leading to the creation of more branches.