A numerical investigation of nuclear coupled density wave oscillations

Abstract

A comprehensive mathematical model of boiling-water reactors (BWRs) for simulating nuclear coupled density wave oscillations is presented. A one-dimensional core dynamics program nars has been developed based on this model. A General Electric BWR/6 system is analyzed using nars. Our analysis shows that, even with very large power oscillations, the amplitude of heat flux oscillations is very low. The reduction in minimum critical heat flux ratio with large power oscillations is also observed to be quite low. Thus it can be concluded that the boiling transition does not occur even at very large power oscillations and hence fuel integrity is not compromised. It has been shown that void reactivity feedback has significant effect on the amplitude of the limit cycle oscillations and always has a destabilizing effect on the system. It is observed that the pressure loss coefficient in jet pumps has a significant effect on the reactor stability. Qualitative results obtained from a wide range of parametric studies on boiling channel stability together with the stability maps in terms of dimensionless numbers are presented. It has been observed that the power profile shape plays a very significant role in the stability of natural circulation loops.