High to low pellet cladding gap heat transfer modeling methodology in an uncertainty quantification framework for a PWR rod ejection accident with best estimate coupling

High to Low modeling approaches can alleviate the computationally expensive fuel modeling in nuclear reactor's transient uncertainty quantification. This is especially the case for Rod Ejection Accident (REA) in Pressurized Water Reactors (PWR) were strong multi-physics interactions occur. In this work, we develop and propose a pellet cladding gap heat transfer (H_gap) High to Low modeling methodology for a PWR REA in an uncertainty quantification framework. The methodology involves the calibration of a simplified H_gap model based on high fidelity simulations with the fuel-thermomechanics code ALCYONE1. The calibrated model is then introduced into the CEA developed CORPUS Best Estimate (BE) multi-physics coupling between APOLLO3^R and FLICA4. This creates an Improved Best Estimate (IBE) coupling that is then used for an uncertainty quantification study. The results indicate that with IBE the distance to boiling crisis uncertainty is decreased from 57% to 42%. This is reflected to the decrease of the sensitivity of H_gap. In the BE coupling H_gap was responsible for 50% of the output variance while in IBE it is close to 0. These results show the potential gain of High to Low approaches for H_gap modeling in REA uncertainty analyses. (authors)