Master Theses & Projects (FESNS)

Permanent URI for this collectionhttps://hdl.handle.net/10155/381

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Browsing Master Theses & Projects (FESNS) by Subject "Applied reactor physics"

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    Investigation of sub-cell homogenization for PHWR lattice cells using superhomogenization factors
    (2016-12-01) Mohapatra, Subhramanyu; Nichita, Eleodor
    To avoid the computational effort associated with full-core neutron transport calculations, full-core neutronics calculations for Pressurized Heavy-Water Reactors (PHWRs) are usually performed in diffusion theory using an approximate core model, whereby only two energy groups are utilized and two-group neutronic properties (i.e. macroscopic cross sections and diffusion coefficients) are homogenized in two dimensions over large sub-domains, each corresponding to a 28.6 cm x 28.6 cm lattice cell. The lattice cell is the elementary geometrical unit describing the rectangular array of fuel channels comprising the PHWR core. The use of lattice-cell homogenization introduces some computational errors. One possible way to reduce such homogenization errors is to sub-divide the lattice cell into sub-cells and perform sub-cell-level homogenization. In this study, the PHWR lattice cell is divided into 3 x 3 sub-cells. Full-cell-averaged, as well as sub-cell-averaged two-group cross-sections, are generated for subsequent use in an equivalent two group two-dimensional diffusion model. Cross sections with Superhomogenization (SPH) [Hebert, 2009] factors are also utilised in an attempt to improve accuracy. The effect of using different homogenization models (full cell, partial cell, partial-cell with SPH-corrected cross sections) is tested on a two-dimensional partial-core model consisting of 3 x 3 lattice cells (bundles). Results from reference transport model with detailed geometry 69-group are compared with cell-homogenized two-group diffusion results obtained using full-cell homogenization and sub-cell homogenization with and without SPH correction factors. The application of sub-cell homogenization, as well as the use of SPH correction factors, is found to have only a minimal effect on computational accuracy.
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    Leakage-corrected discontinuity factors for a second-generation Th-Pu pressure-tube SCWR.
    (2014-08-01) Carisse, Katarzyna; Nichita, Eleodor
    The neutron flux throughout a reactor core should be calculated, ideally, by solving the neutron transport equation for a highly detailed geometric model of the core. Since this is computationally impractical, approximate node-homogenized models have historically been used whereby neutronic properties are averaged over cartesian parallelepipedic regions called nodes. This process is referred to as homogenization. The simplest homogenization procedure is known as standard homogenization. Standard homogenization calculates node-homogenized cross sections as flux-weighted averages over the volume of each node. It uses an approximate spatial flux distribution obtained from single-node detailed-geometry calculations that approximate the node-boundary conditions to be reflective. While standard homogenization has been successfully used for CANDU reactors, there exist more advanced homogenization methods such as Generalized Equivalence Theory (GET). GET improves accuracy by allowing the neutron flux in the node-homogenized model to be discontinuous at node boundaries through the use of discontinuity factors. Node-averaged cross sections and discontinuity factors can be obtained from single-node calculations using reflective boundary conditions. To further improve accuracy, non-reflective boundary conditions that approximate the real node-boundary conditions can be used; a process known as leakage correction. This work explores the use of GET with leakage-corrected cross sections and discontinuity factors for the next-generation PT-SCWR flux calculations. Results show that using GET in conjunction with leakage corrections yields substantial improvements in accuracy over standard homogenization and should be given serious consideration as a method for performing neutronic calculations for PT-SCWR cores.