| 1. |
- Dufek, Jan, 1978-
(författare)
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Complex models of nodal nuclear data
- 2011
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Ingår i: International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011). - 9788563688002
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Konferensbidrag (refereegranskat)abstract
- During the core simulations, nuclear data are required at various nodal thermal-hydraulic and fuel burnup conditions. The nodal data are also partially affected by thermal-hydraulic and fuel burnup conditions in surrounding nodes as these change the neutron energy spectrum in the node. Therefore, the nodal data are functions of many parameters (state variables), and the more state variables are considered by the nodal data models the more accurate and flexible the models get. The existing table and polynomial regressionmodels, however, cannot reflect the data dependences on many state variables. As for the table models, the number of mesh points (and necessary lattice calculations) grows exponentially with the number of variables. As for the polynomial regression models, the number of possible multivariate polynomials exceeds the limits of existing selection algorithms that should identify a few dozens of the most important polynomials. Also, the standard scheme of lattice calculations is not convenient for modelling the data dependences on various burnup conditions since it performs only a single or few burnup calculations at fixed nominal conditions. We suggest a new efficient algorithm for selecting the most important multivariate polynomials for the polynomial regression models so that dependences on many state variables can be considered. We also present a new scheme for lattice calculations where a large number of burnup histories are accomplished at varied nodal conditions. The number of lattice calculations being performed and the number of polynomials being analysed are controlled and minimised while building the nodal data models of a required accuracy.
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| 2. |
- Larsson, Viktor, 1984, et al.
(författare)
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NEUTRON NOISE CALCULATIONS IN THREE-DIMENSIONAL SYSTEMS
- 2011
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Ingår i: Proc. of International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering 2011. - 9788563688002
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Konferensbidrag (refereegranskat)abstract
- In this paper, the neutron noise, i.e. the stationary fluctuations of the neutron flux around its mean value, is calculated in three dimensions and two energy groups using diffusion theory. Cross-sections and other reactor parameters are realistic data coming from a commercial PWR. This work is an extension of a previous model which used finite differences in two dimensions for the spatial discretization. In this work, the calculations are still performed using finite differences for the spatial discretization, but the neutron currents and neutron noise currents are corrected using the Analytical Nodal Method. Another correction is performed by introducing discontinuity factors to improve the modelling of leakages at the face between the fuel assemblies.
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