Improvement of the SCDAP/RELAP5 code with respect to FZK experimental facilities

The USNRC severe core damage code SCDAP/RELAP5 mod 3.2 was extended to simulate adequately integral out-of-pile facilities at Forschungszentrum Karlsruhe (FZK). The original model for the CORA electrical heater rod was extended to allow a complete analysis of the whole test section. In addition, in the axial heat conduction module the axial boundary conditions were improved, and the radiation across annular gaps is now taken into account. Furthermore, to allow a fine simulation of reflood cond itions, the number of axial zones has been increased to 36, allowing a fine mesh of ∼ 0.05 m. A new approach of clad failure estimation is included, based on FZK separate effect tests, but not fully tested. Together with error corrections, the code is now a reliable basis to support considerably the experiments in the QUENCH facility with pre-test calculations and post-test analyses as demonstrated by several calculations. In addition, more reliable calculations of accident scenarios and related accident management measures are possible for existing and future commercial power plants.