A lattice Boltzmann framework to simulate boiling water reactor core hydrodynamics

This paper presents a consistent LBM formulation for the simulation of a two-phase water steam system. Results of initial model validation in a range of thermodynamic conditions typical for Boiling Water Reactors (BWRs) are also shown. The interface between the two coexisting phases is captured from the dynamics of the model itself, i.e., no interface tracking is needed. The model is based on the Peng Robinson (P R) non-ideal equation of state and can quantitatively approximate the phase-coexistence curve for water at different temperatures ranging from 125 to 325 C. Consequently, coexisting phases with large density ratios (up to 1000) may be simulated. Two-phase models in the 200 300 C temperature range are of significant importance to nuclear engineers since most BWRs operate under similar thermodynamic conditions. Simulation of bubbles and droplets in a gravity-free environment of the corresponding coexisting phase until steady state is reached satisfies Laplace law at different temperatures and thus, yield the surface tension of the fluid. Comparing the LBM surface tension thus calculated using the LBM to the corresponding experimental values for water, the LBM lattice unit (lu) can be scaled to the physical units. Using this approach, spatial scaling of the LBM emerges from the model itself and is not imposed externally.