SIMULTANEOUS BOTTOM AND TOP-DOWN REWETTING CALCULATIONS WITH THE CATHARE CODE

A top-down reflooding model was developed and implemented into the Fre nch best-estimate thermal-hydraulic code CATHARE2 V1.3E. A two-dimensi onal mesh moving along the wall with the quench front is used to resol ve the heat conduction equation in the wall near the quench front. The results of the model validation and the first assessment calculations are given. The Winfrith single-tube top-down reflooding experiments w ere used to validate the model. The influence of wall material, pressu re, mass flux, and wall temperature on the quench front velocity are c orrectly predicted. The REWET-II and PERICLES experiments in rod bundl e geometry were used to assess the capabilities of the code to predict simultaneous bottom and top-down rewetting. Comparison of the calcula ted results with the REWET II experimental data shows the ability of t he new package to calculate the key features of this complex experimen t. The existence and progression of two quench fronts in the core are correctly predicted. The maximum cladding temperatures are overpredict ed for experiments with combined and upper plenum injection. This diff erence, which is attributed to a too severe counter current flow limit (CCFL) calculated by the code, does not exceed 150-degrees-C. With th e top-down reflooding option, improved predictions of wall temperature s in the upper part of the core in the PERICLES tests with respect to the previous version of the code were obtained, since th is part of th e core was rewetted by top-down quenching. To realize further improvem ents in combined reflooding calculations, the CCFL predicting capabili ties of CATHARE should be addressed first. More detailed experimental information and additional data would also be required for in-depth as sessment of the models.