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The solution manifold of the system of nonlinear differential equations representing a BWR needs to be examined to understand its dynamical behavior. In particular, stable or unstable fixed points and stable or unstable oscillatory solutions (or turning points/saddle node bifurcations) are of paramount interest. In this framework integrated BWR (system) codes and simplified BWR models (reduced order models, ROM) are used together to reveal the solution manifold of the nonlinear differential equations describing the system. This work is a continuation of the previous work at the Paul Scherrer Institute (PSI, Switzerland) and University of Illinois (USA) on this field. The ROM developed at PSI was upgraded by introducing the recirculation loop, subcooled boiling and modification to the feedback reactivity calculation. The upgraded ROM has been coupled with the BIFDD code which performs semi-analytical bifurcation analysis. The methodology and some results of the semi-analytical bifurcation analysis of the modified ROM will be demonstrated and discussed. The stability boundary (SB) and the nature of the Poincare-Andronov-Hopf bifurcation (PAH-B) are determined and visualized in appropriate two-dimensional parameter maps. Furthermore, for independent confirmation of the results, numerical integrations of the ROM differential equations have been carried out in the MATLAB environment.

ICONE15-10568 ADVANCED BWR STABILITY ANALYSIS WITH A REDUCED ORDER MODEL AND SYSTEM CODE