The 'hot rod methodology' for intermediate break LOCA calculations with the CATHARE2 code

The nuclear fuel that will be used for next decades in French PWR may be quite different from current ones, including technological evolutions of cladding alloys, new types of assemblies, etc. Beside these structural evolutions, calculation methodologies are also changing with the use of Best-estimate multi-physics multi-scale coupled calculations, and complex physical models development at 3D local scale. In the frame of its LOCA R and D program, the French 'Institut de Radioprotection et de Surete Nucleaire' is developing its own calculation methodology to figure out the maximum cladding temperature and the maximum oxidation rate reached by the hottest rod in the core. This HOT ROD methodology has been worked out for Intermediate Break LOCA calculations using the 'Best-Estimate' CATHARE2 system code. This calculation is based on a first modeling called 1D SYSTEM calculation which simulates the thermohydraulical behavior of the whole reactor. During this computation, key parameters are stored at core ends in order to be used as boundary conditions for a second calculation called 1D CHAINED calculation nodelizing in one dimension the hottest assembly of the core. Based on experimental evidences, the hot assembly has been considered to have no influence on the thermohydraulical behavior of the mean core. Hence its hydraulical environment has been modified at each calculation's timestep in order to fit with the SYSTEM mean one. This paper details the methodology's validation phase on PERICLES 2D BOIL-UP tests, which have quite the same swollen-level evolution's rate as in the boil up phase of an intermediate break LOCA. (author)