Xenon-Induced Spatial Power Oscillations in the 400MW PBMR. Presentation

The redistribution of the spatial Xenon concentration in the 400MW PBMR core [1] has a non-linear, time-dependent feedback effect on the spatial power density during several types of operational transient events. Due to the inherent weak coupling that exists between the Iodine and Xenon formation and destruction rates, as well as the complicating effect of spatial variance in the thermal flux field, reactor cores have been analyzed for a number of decades for the occurrence and severity of Xenon-induced spatial power oscillations. Of specific importance is the degree of oscillation damping exhibited by the core during transients, which involves spatial variations in the local power density. In this paper the TINTE [2] reactor dynamics code is used to assess the stability of the current 400MW PBMR core design with regard to Xenon oscillations. The focus is mainly on the determination of the inherent Xenon and power oscillation damping properties by utilizing a set of hypothetical CR insertion transients at various power levels. The oscillation damping properties of two 100-50- 100% load-follow transients, one of which includes the destabilizing spatial effects of moving Control Rods (CRs), are also discussed in some detail. The study shows that, although first axial mode oscillations do occur in the 400MW PBMR core, the inherent damping of these oscillations is high, and that none of the investigated load-follow transients resulted in diverging oscillations. It is also shown that the PBMR core exhibits no degree of radial Xenon-induced spatial power oscillations. (author)