Nuclear coupled thermal–hydraulic analysis of parallel channel density wave instabilities in a supercritical water reactor

Abstract

In an attempt to obtain a realistic estimate of the density wave instability (DWI) thresholds of a typical supercritical water reactor (SCWR) in its relevant operating regime, the present numerical framework accounts for the nonlinear interdependence among the thermal–hydraulic (TH), neutronic and fuel dynamic field variables, by solving the coupled multi-physics conservation equations in a time-domain where the TH, neutron point-kinetic (NPK) and fuel heat conduction (FHC) solvers are integrated through coolant density and fuel temperature reactivity feedback coefficients, and supercritical water (SCW) heat transfer coefficient (HTC). The time dependent and radially non-uniform, but axially uniform reactor power distribution among the different fuel assemblies (FAs) are incorporated in the numerical framework by the employment of NPK solver and considering the existence of several parallel channels in the reactor core where every channel represents a group of FAs of similar reactor power assembled in a single region. The integrated model is next compared against the available numerical results to access its capability in analyzing thermal-hydraulically induced DWIs while being influenced with the neutronic reactivity feedback effects. Nuclear coupled core-wide and regional density wave oscillations (DWOs), two modes of parallel channel DWIs, are finally analyzed with the purpose to determine the effect of temporal reactor power variation and the channel to channel interactions on the stability thresholds of the SCWR under consideration. The conclusions are drawn and reported accordingly.