Abstract
The distribution of the power inside a reactor core can be described by the time dependent multigroup neutron diffusion equation. One of the approaches to integrate this time-dependent equation is the modal method, that assumes that the solution can be described by the sum of amplitude function multiplied by shape functions of modes. These shape functions can be computed by solving a _-modes problems. The modal method has a great interest when the distribution of the power cannot be well approximated by only one shape function, mainly, when local perturbations are applied during the transient. Usually, the shape functions of the modal methods are updated for the time-dependent equations with a constant time-step size to obtain accurate results. In this work, we propose a modal methodology with an adaptive control time-step to update the eigenfunctions associated with the modes. This algorithm improves efficiency because of time is not spent solving the systems to a level of accuracy beyond relevance and reduces the step size if they detect a numerical instability. Step size controllers require an error estimation. Different error estimations are considered and analyzed in a benchmark problem with a out of phase local perturbation.
Highlights
The distribution of the neutrons inside a reactor core along time can be described by the time dependent multigroup neutron diffusion equation
The shape functions of the modal methods are updated for the time-dependent equations with a constant time-step size to obtain accurate results [3]
The methodology proposed is compared with the backward differential method (BKM) [1]
Summary
The distribution of the neutrons inside a reactor core along time can be described by the time dependent multigroup neutron diffusion equation. The shape functions of the modal methods are updated for the time-dependent equations with a constant time-step size to obtain accurate results [3]. Recent time schemes have been developed to select automatically an appropriate step size from a given tolerance These algorithms have the advantage that they do no wast time for solving the systems to a level of accuracy beyond relevance and reduce the step size if they detect a numerical instability. We propose an adaptive control time-step for the modal methodology to integrate the time-dependent neutron diffusion equation
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