Transient dryout prediction using a computationally efficient method for sub-channel film-flow analysis

• A simplified three-field sub-channel model for BWR dryout prediction is proposed.
• Fast and robust simulations of both transient and steady-state conditions are obtained.
• The model is validated with several hundred transient dryout measurements.
• Dryout power can be predicted with a standard-deviation of about 4%.

A simplified three-field sub-channel model for prediction of dryout in BWR fuel assemblies under steady-state as well as transient conditions is presented. Fast and robust calculations are achieved by decoupling the conservation equations for the liquid film from the solution of the sub-channel problem, which relies on a traditional two-field model. The liquid films, which are attached to various walls can then be analyzed as a post-process, effectively extending the two-field sub-channel code to a three-field code. The model has been validated with thousands of steady-state and hundreds of transient dryout measurements in full-scale fuel-bundle mock-ups under realistic conditions. The results show that it is possible to predict the dryout power with a standard deviation of about 4% for both steady-state and transient conditions using only a minimum of model calibration to account for details in the spacer grid design.