Development of a Nonlinear Thermal-Hydraulic Model to Analyze Parallel Channel Instability of Boiling Water Reactor Core Undergoing In-Phase and Out-of-Phase Modes of Oscillations

ABSTRACT

The objective of the paper is to present a thermal-hydraulic model, used for simulating two-phase flow boiling systems, which will simulate parallel channel instability in a boiling water reactor core undergoing in-phase and out-of phase modes of oscillations. The multiple parallel channels present in the reactor core can undergo in-phase or out-of-phase modes of instabilities depending on the operating conditions of the reactor. To simulate both the modes of instabilities, steady state and transient models are to be developed first and then, need to be integrated together with appropriate boundary conditions. The present paper explicitly (i) defines the boundary conditions, (ii) presents the methodology adopted to model both the instability modes separately, (iii) demonstrates the capability to analyze such parallel channel instability for both forced and natural circulation systems and (iv) confirms the existence of type-I and type-II instabilities in appropriate conditions.

Keywords: Thermal-hydraulic model, Density wave oscillations, Boiling water reactor, Parallel channel instability, In-phase and out-of-phase modes of oscillations.

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