Modal Decomposition Method for-BWR Stability Analysis

Abstract

In-phase and out-of-phase instabilities have been observed in BWR reactors. To improve the safety systems of these reactors, it is necessary to be able to detect in a reliable way these oscillations from the neutronic signals. In this paper a methodology to decompose the neutronic signals in its modal amplitudes is proposed. This decomposition is based on the normal and the adjoint dominant Lambda modes of a static configuration of the reactor core. The calculation of these eigenmodes for a realistic problem is reviewed and the oscillation parameters for the modal decompositions of the neutronic signals from Ringhals reactor have been calculated using the proposed methodology.

KEYWORDS:

• modal decomposition
• Lambda modes
• neutronic signals
• in-phase and out-of-phase instabilities
• BWR type reactors