BWR stability and bifurcation analysis using a novel reduced order model and the system code RAMONA
Abstract
Boiling water reactor (BWR) stability analysis is usually carried out using large system codes. However, because of the large computational efforts required, such codes cannot in practice be employed for the detailed investigation of the complete manifold of solutions of the nonlinear differential equations describing the BWR system. In this context, reduced order models, containing a minimum number of system equations describing the most important physical phenomena, become necessary to provide deeper insight into the physical mechanisms underlying the different instability phenomena observed in BWRs, e.g. in-phase and out-of-phase power oscillations. A novel analytical, reduced order model has been currently developed to simulate the different types of instabilities encountered in heated channels and BWRs, viz. density wave oscillations (DWOs), as well as in-phase and out-of-phase oscillations in the reactor core. The complete model comprises three main parts: spatial lambda- mode neutron kinetics with the fundamental and first azimuthal modes, fuel heat conduction dynamics, and core thermal- hydraulics based on a drift flux model representation of the two-phase flow. Stability and semi-analytical bifurcation analysis is carried out for a purely thermal-hydraulic system (heated channel), as well as for a complete BWR (represented via two-channel nuclear-coupled thermal-hydraulics), using the current reduced order model in conjunction with the bifurcation code BIFDD. The…
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