Abstract
This paper mainly focuses on the hot assembly hot rod (HAHR) calculations of a small break loss of coolant accident (SBLOCA) transient with a description of the standalone hot assembly model (SAHASB), which takes advantage of the new capabilities implemented in the CATHARE2 V2.5_1 computer code, and the hot rod statistical method (HRSM), which adds statistical treatment of HAHR uncertainties to the current deterministic reactor coolant system (RCS) thermal hydraulic calculation. Using boundary conditions taken from 1D or 3D RCS transient calculations, HAHR calculations are performed in order to simulate the split into a wet and a dry region making allowance for the effects of rod bundle power, cross-flow redistribution, flow diversion due to flow blockage and hot rod thermo-mechanics. Thanks to the fast running feature of SAHASB, a non-parametric method based on direct CATHARE calculations can be used to propagate HAHR uncertainties. From the distribution of results, a statistical analysis makes it possible to determine PCT and cladding oxidation at a 95/95 percent confidence level, thus eliminating too improbable conservative results. The related gain in margins can be useful for relaxing unnecessary constraints on reactor operations or fuel management flexibility.
