Study of flow instability in MTR-reactors during natural circulation

Abstract EN

Flow instabilities are most common operating problems in two-phase flow systems such as conventional boilers, steam generators and nuclear reactors.

They are undesirable since they can degrade the system performance and cause serious control problems.

In this paper, a procedure for predicting the onset of flow excursion instability in downward and upward flows, through a vertical heated channel of a specified MTR-Reactor at low-pressure and low-flow conditions without boiling, is presented.

A detailed analysis of the pressure drop components for a downward and upward flow in the heated channel is carried out to study the possibility of unstable transition from single-phase flow to high-quality two-phase flow, i.e.

flow excursion.

Both the developed model and RELAP5 Code are used in this study.

Effect of different parameters like reactor power, inlet subcooling and flow rate are studied.

Low flow rate and high subcooling are the two important conditions for the occurrence of this type of instability.