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Development of fine-mesh methodologies for coupled calculations in Light Water Reactors

Klas Jareteg (Institutionen för fysik, Subatomär fysik och plasmafysik (Chalmers))
Gothenburg : Chalmers University of Technology, 2017. ISBN: 978-91-7597-626-6.

This thesis presents fine-mesh multiphysics methodologies and algorithms for
numerical predictions of the behavior of Light Water Reactor (LWR) cores. The
multiphysics aspects cover the distribution of neutrons, the fluid flow of the
coolant and the conjugate heat transfer between the solid fuel pins and the
fluid coolant. The proposed schemes are aimed at fine-mesh coupled effects,
directly resolving the interdependencies of the different fields on the finest
scales of the computations.

The solver is developed for both steady-state and transient LWR scenarios. For
the steady-state simulations, the neutronics is solved both by the lower order,
diffusion equation and the higher order, discrete ordinate transport method,
and for transient cases by the former. The thermal-hydraulic solver is based on
a computational fluid dynamics (CFD) approach. The implementation utilizes a
finite volume method (FVM) computational framework, and to achieve feasible
computational times, high performance computing (HPC) aspects such as
parallelization by domain decomposition are considered.

The implemented tool is applied to cases of parts of a fuel assembly, analyzing
systems of up to 15x15 fuel pins and succesfully resolving sub-pin
resolution of all fields. Furthermore, the transient fine-mesh neutronic solver
is verified based on a novel scheme utilizing the system response to a local

In addition, the multiphase flow problem encountered in Boiling Water Reactors
(BWRs) is studied. First, the transport of bubbles under subcooled boiling
conditions is simulated based on a population balance approach. The novel
formulation is shown to increase the computational efficiency and to capture a
large range of bubbles sizes with few degrees of freedom. Second, the
typical Eulerian-Eulerian approach for two-phase flow is studied from a
stability and dynamics perspective. The latter investigations highlight the
complexity of the two-fluid formulation and indicate the spontaneous emergence
of meso-scale void structures under adiabatic conditions.

Nyckelord: multiphase flow, CFD,nuclear reactor multiphysics,Coupled neutronics/thermal-hydraulics

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Denna post skapades 2017-08-29. Senast ändrad 2017-09-05.
CPL Pubid: 251490