Sensitivity Studies on uncertainty parameters and code modeling of calandria vessel integrity during late phase CANDU 6 severe accident

The present focus on the analysis of the coolability of a calandria vessel starting with a dry debris bed. The calculation are performed with SCDAP/RELAPSIM/MOD3.4 code version and using COUPLE routines modified to properly use the option for a horizontal cylinder. Parametric studies are performed in order to quantify the effect of several identified sources of uncertainty on calandria vessel (CV) failure: metallic fraction of zirconium inside the debris, containment pressure, timing of water depletion inside calandria vessel, Reactor Vault (RV) nodalization and, the gap heat transfer coefficient. The main outcome of the calculations is the identification of possible source of uncertainty and modality to improve the accuracy of results. Also the results obtained confirm the capability of the heat removal from the CV wall by the RV water, as long as the liquid phase is present in the tank