Influence of the spacer location and the direct heating in the single and two phase region on the development of in-phase instabilities of boiling water reactors

Abstract

The dynamic of boiling flows can be considered as a complex problem where generally more than one instability mechanism is present. This problem of two-phase flow instabilities is found in a big variety of energy and chemical engineering systems such as the channels of Boiling Water Reactors (BWR), conventional steam boilers, and phase change heat exchangers used in the chemical industry. Among the different instability types, one of the most important for the nuclear engineering field is the in-phase instability that appears in boiling water reactors (BWR). In this instability type a synchronized oscillation of the power and the thermal-hydraulic variables is produced in all the channels of the reactor. This paper study the influence of the spacer location and the direct heating i.e. the heating of the boiling channels by neutron and gamma rays on the in-phase instabilities BWRs.