BWR linear stability analysis

Abstract A state-of-the-art analytical model has been developed for investigating the linear stability of boiling water nuclear reactors (BWR). This model has been implemented into a computer code named NUFREQ-NP. The NUFREQ-NP code permits an investigation of the stability of a single heated channel, as well as the multi-channel core of a BWR. It accommodates various neutronics models, including point kinetics, one-dimensional, two-dimensional, and three-dimensional neutron kinetics. It is capable of evaluating system stability in terms of any of the following perturbed state variables: inlet flow rate, external reactivity, and system pressure. This paper presents the modeling principles used in NUFREQ-NP to describe the transient two-phase flow and heat transfer phenomena. Special emphasis is placed on those aspects of the model development which are related to variable system pressure effects. Also, the derivation of various transfer functions is given. The results of NUFREQ-NP testing and verification include a parametric study of the effects of various modeling assumptions, and comparisons with both out-of-core and in-core-experimental data. These comparisons indicate very good agreement between the calculated and measured system transfer functions.