An Improved Water Density Feedback Model for Pressurized Water Reactors

Accurate and economical methods have been developed to model water density feedback in diffusion calculations for application to pressurized water reactors. Spectral variations of the two-group macroscopic cross sections are accurately modeled by second-order polynomials in water density. Open channel and subcooled boiling effects on the core’s water density distribution are evaluated by coupling three-dimensional thermal-hydraulic and neutron diffusion computer codes. The costly requirement of numerical mesh compatibility between these codes is removed without loss of accuracy. The margin to fuel degradation limits during accident conditions is found to increase when the improved feedback model is employed, serving as a stimulus for further usage.