Abstract
Because of the double-heterogeneity (DH), dispersed particle-type systems cannot be described by traditional neutronic programs, and the volumetric homogenization method (VHM) will bring reactivity calculation deviation because of ignoring the spatial self-shielding effect of the particles. In this article, the relationship between the reactivity calculation deviation and the optical length of dispersed particle-type fuel and different types of burnable poisons is analyzed. Also then, it was proposed that the influencing factors of reactivity calculation deviation can be integrated to a physical quantity named theoretically modified optical length containing the influencing factors mentioned earlier. In addition, the DH physical boundary has forward that, when the theoretically modified optical length is larger than 10−4, reactivity calculation deviation of volumetric homogenization method will be larger than 100 pcm, and the DH of the dispersed particle-type systems should be considered.
Highlights
Particle-dispersed fuel can contain fission products under high temperature and deep burnup conditions and block the release of fission gas and fission fragments out of the fuel pellets
Particle-dispersed fuels and burnable poisons have gradually attracted attention and applications due to the excellent characteristics mentioned earlier, but they have doubleheterogeneity (DH), which cannot be described by traditional neutronic calculation programs
For different burnable poison materials, under the same particle size, particle volumetric fraction, and matrix fuel enrichment, the reactivity calculation deviation of the volumetric homogenization method (VHM) is directly related to the absorption cross-section of the burnable poison
Summary
Particle-dispersed fuel can contain fission products under high temperature and deep burnup conditions and block the release of fission gas and fission fragments out of the fuel pellets. To comprehensively analyze the size of the DH of the cells containing different particle-dispersed burnable poison materials, the calculation deviations of different types of burnable poison particle systems will be compared, and the factors of different matrix fuel enrichment and poison particle volumetric fraction will be considered. For different burnable poison materials, under the same particle size, particle volumetric fraction, and matrix fuel enrichment, the reactivity calculation deviation of the VHM is directly related to the absorption cross-section of the burnable poison. For a fuel cell, when the volumetric fraction of particles and the fuel enrichment of the matrix are determined, a very small particle size, such as the radius of 10 μm, can be used to calculate the material cross-section of the dispersed particles without self-shielding. When the size of the dispersed particles is greater than a certain value, the theoretically modified optical length calculated according to the Eq 2 is greater than the limit 10−4, the calculation deviation of VHM will be greater than 100 pcm, and the DH of the system needs to be considered
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