NUFREQ-NP: A Computer Code for the Stability Analysis of Boiling Water Nuclear Reactors

The phenomena of nuclear coupled density-wave oscillations are of considerable importance in the stability analysis of boiling water nuclear reactors (BWRs). A state-of-the-art linear-frequency-domain digital computer code, NUFREQ-NP, has been developed for either forced- or natural-circulation BWR stability analysis. The NUFREQ-NP code can be excited by many external perturbations, including system pressure perturbation. It is based on one-dimensional drift-flux thermal hydraulics, and allows for subcooled boiling, arbitrary nonuniform axial and radial power shapes, distributed local losses (e.g., spacers), and detailed fuel element dynamics. NUFREQ-NP has been compared with the experimental data for the Peach Bottom-2 stability tests, and good agreement has been found.