Análise de instabilidades em reatores a água fervente: cálculo dos parâmetros decay ratio e frequência natural

Abstract

Boiling water reactors are susceptible to instabilities, causing fluctuations in reactor power in regions of high power and low coolant flow. During reactor startup there is a greater probability that these regions of instability are present; another reason could be due to transient processes in some reactor parameters. The analysis of the temporal evolution of the power reveals a stable or unstable process after disturbance in a light water reactor of the BWR type (Boiling Water Reactor). In this work, the time series model known as ARMA (Auto Regressive Moving Average model) was used to calculate the decay ratio, or Decay Ratio (DR), and the natural frequency (NF) resulting from oscillations in the reactor power. Matlab code was used for this purpose. This document also presents a comparison of calculated DR and NF values ​​with DRIA and DRAT codes developed by the University of Pennsylvania.