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Fission Product Release as a Function of Chemistry and Fuel Morphology
Published in J. T. Rogers, Fission Product Transport Processes in Reactor Accidents, 2020
R. R. Hobbins, D. J. Osetek, D. A. Petti, D. L. Hagrman
The chemistry of uranium dioxide fuel changes as a function of burnup due to the production of fission products and the concomitant increase in the oxygen-to-metal (0/M) ratio. However, the 0/M ratio is only a weak function of burnup indicating that burnup has a relatively small influence on the oxidation state of fission products under accident conditions. The main effect of burnup is on the concentration of fission products, the distribution of fission products within the fuel, and the fuel structure itself. The uranium dioxide undergoes restructuring as a function of burnup resulting in the formation of fission gas bubbles on grain boundaries that tend to interlink to form tunnels along grain edges at burnups above _ 5,000 MWd/MtU. This restructuring is enhanced by irradiation at higher powers and elevated fuel temperatures. During irradiation, fission gases and vapors migrate to the grain boundaries and, if tunnels have developed, the gas bubbles can be released fairly easily to the gap outside the fuel pellets. Grain boundary tunnels also provide a pathway for volatile fission product release during fuel heatup under accident conditions. The GRASS family of computer codes[l] explicitly models these changes in fuel morphology as a function of burnup. However, it has been found that simple Booth diffusion modeling gives results that are in good agreement with in- and out-of-pile experimental data[2,3] by varying the effective diffusion distance. Burnup can enhance release by a factor of as much as thirty at a burnup of 47,000 MWd/MtU[4].
Neutronics
Published in Kenneth D. Kok, Nuclear Engineering Handbook, 2016
The primary consequence of burnup is a drop in k-effective as the fuel burns out and fission products are built up. This drop is compensated by the build-up of new fissile isotopes (notably Pu-239 from U-238 neutron absorption in uranium-fueled reactors). Generally, boiling water reactors and pressurized water reactors replace the fuel in stages, with fresh fuel assemblies replacing the most burned-out assemblies at scheduled shutdowns with nonreplaced assemblies often moved (shuffled) to new positions to optimize the reactor operating characteristics.
B
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
bulb generator Off-line BIST suspends normal operation and is carried out using built-in test pattern generator and test response analyzer (e.g., signature analyzer). bulb generator a free-standing generator contained in a streamlined, waterproof bulb-shaped enclosure and driven by a water-wheel resembling a ship's propeller on a shaft which extends from one end of the enclosure. They are used in tidal power installations. See tidal power. bulk power a term inclusive of the generation and transmission portions of the power system. bulk scattering scattering at the volume of an inhomogeneous medium, generally also possessing rough boundaries. It is due to inhomogeneities in the refractive index. bulk substation a substation located on a highvoltage transmission line which supplies bulk power to a non-generating utility. bulldog an attachment for a wire or hoist. buried via a via connected to neither the primary side nor the secondary side of a multilayer packaging and interconnecting structure, i.e., it connects only internal layers. burndown breakage of an overhead electric power line due to heating from excess current. burnup a measure (e.g., megawattt-days/ton) of the amount of energy extracted from each unit of fissile material invested in a nuclear reactor. burn-in component testing where infant mortality failures (defective or weak parts) are screened out by testing at elevated voltages and temperatures for a specified length of time. burst refresh in DRAM, carrying out all required refresh actions in one continuous sequence--a burst. See also distributed refresh. burst transfer the sending of multiple related transmissions across an interconnect, with only one initialization sequence that takes place at the beginning of the burst. burstiness factor used in traffic description, the ratio of the peak bit rate to the average bit rate. bus (1) a data path connecting the different subsystems or modules within a computer system. A computer system will usually have more than one bus; each bus will be customized to fit the data transfer needs between the modules that it connects. (2) a conducting system or supply point, usually of large capacity. May be composed of one or more conductors, which may be wires, cables, or metal bars (busbars). (3) a node in a power system problem (4) a heavy conductor, typically used with generating and substation equipment. bus acquisition the point at which a bus arbiter grants bus access to a specific requestor.
Absolute quantification of 137Cs activity in spent nuclear fuel with calculated detector response function
Published in Journal of Nuclear Science and Technology, 2023
Shunsuke Sato, Yasushi Nauchi, Takehito Hayakawa, Yasuhiko Kimura, Takao Kashima, Kazuhiro Futakami, Kenya Suyama
The implementation of burnup credit enables the efficient design of transport casks and storage facilities for spent nuclear fuels [1–3]. To apply the burnup credit, a measurement is needed to confirm the conservatism of isotopic composition for the criticality safety assessment [4,5], and burnup of spent nuclear fuel, in general, is estimated by measurement to confirm the conservatism. The burnup of spent nuclear fuel, which is defined as the total amount of released energy per mass of initial heavy metal in fuel (GWd/t) or the fraction of fuel metal atoms that undergo fission per initial metal atom (%FIMA) [1], is difficult to measure non-destructively. Thus, a burnup indicator, or a parameter corresponding to burnup, is alternatively measured non-destructively, and the burnup is indirectly confirmed by the relationship between the burnup indicator and burnup evaluated by a depletion calculation based on a reactor record [3].
High-Resolution Gamma-Ray Spectrometry of Pebble Bed Reactor Fuel Using Adaptive Digital Pulse Processing
Published in Nuclear Technology, 2023
Shefali Saxena, Ayman I. Hawari
The PBR is a high-temperature gas-cooled nuclear reactor. Its core consists of spherical fuel elements called pebbles, and its operation depends on online refueling. The reactor is continuously refueled with fresh or reusable fuel pebbles from the top of the reactor, and pebbles are continuously cycled through the core until they reach an end-of-life burnup limit. Burnup is defined as the energy generated per unit mass of fuel and is typically reported in units of megawatt days per metric ton [tonne] of uranium (MWD/MTU). Gamma-ray spectrometry can be used for online interrogation of PBR fuel for determination of the burnup level on a pebble-by-pebble basis. For each discharged fuel pebble, its burnup is measured by an online burnup monitoring system to determine if it reaches a prescribed end-of-life burnup limit (e.g., 100 000 MWD/MTU). If not, it will be reloaded back to the core. Otherwise, it is discarded from the bottom of the core to the spent fuel facility.1,2 Accurate determination of burnup requires high-resolution, high-throughput, real-time gamma-ray measurements.3,4
Study of the Effects of Moderators on ADS System Performance Based on UN-ThO2 Fuel
Published in Nuclear Science and Engineering, 2021
A. M. M. Ali, Hanaa H. Abou-Gabal, Nader M. A. Mohamed, Ayah E. Elshahat
The amount of thermal energy generated from nuclear fuel varies with the type and the percentage of the fissile material of the fuel.10 The fraction of the power obtained from the fuel in a reactor is called the burnup.11 Therefore, it is very important to obtain the fraction of energy extracted from each fuel type for all cases. Figure 15 shows the power fraction of the UN seed fuel and the ThO2 blanket fuel for all cases. It can be observed that more power extraction can be obtained from the ThO2 blanket fuel in the LW case due to the higher fission cross section of 233U with the thermal neutrons. On the other hand, the seed fuel of the LW case contributes power with a lower fraction than the other two cases because of the lower content of the fissile isotopes (235U) at the BOC. Consequently, for the LW case, the fuel burnup will be higher than the other two cases, or by another meaning lower content of fissile materials at the end of the ADS cycle.