Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

According to German requirements for LOCA analyses, it has to be proven in addition to the common safety criteria that less than 10% of the fuel rods rupture during the accident. In order to perform such core damage extent analysis, a newly developed model of a generic German Pressurized Water Reactor is presented. The model developed with the system code ATHLET-CD includes four loops and a detailed configuration of the reactor pressure vessel. A 3D parallel channel approach is applied for the downcomer, lower and upper plenum and the core, which is modelled by 193 thermal-hydraulic channels (one channel per fuel assembly) and multiple rods per channel in order to represent the power distribution in a sufficiently accurate way. New for such detailed system code analyses is that the deformation and burst of the fuel rods and the feedback to thermal hydraulics by reduction of the flow cross-sections is taken into account. The number of failed rods has been determined for best-estimate and top-peaked power profiles and has been compared to the 10% criterion. Furthermore, the large-break LOCA leads to asymmetric thermal-hydraulic boundary conditions at the RPV inlets and outlets because of break of only 1 out of 4 loops, asymmetric emergency core-cooling due to postulated outage and/or malfunction of certain trains and the influ-ence of the pressurizer. In contrast to previous studies, an asymmetric distribution of the failed rods within the core is observed, depending on the location of break, pressurizer and available ECCS injection.