Analyses of the OECD - MSLB Benchmark with the Codes DYN3D and DYN3D/ATHLET

The code DYN3D coupled with the thermal-hydraulic plant model ATHLET was used for the analysis of the OECD Main Steam Line Break (MSLB) Benchmark which is based on real plant design and operational data of the TMI-1 PWR. DYN3D is a three-dimensional core model for steady-state and transient analyses of thermal reactors with quadratic or hexagonal fuel as-semblies. The neutron kinetic model is based on the solution of the three-dimensional two-group neutron diffusion equation by nodal expansion. Models for the thermal hydraulics of the reactor core and the fuel pins are implemented in the DYN3D. The reactor core is modeled by parallel cooling channels which can describe one or more fuel elements. DYN3D can be used as a stand alone code with given thermal-hydraulic boundary conditions of the core. Besides the standard simulation given by the specification, modifications are introduced for sen-sitivity studies. The results presented here show the influence of a reduced number of thermal-hydraulic channels for the core for the exercise 2 and the influence of coolant mixing inside the reactor pressure vessel exercise 3. Based on the presented investigations, it can be concluded that the maximum values of local parameters as fuel temperatures are not conservative, if a few number of coolant channels is used for the simulation of the reactor core. If coolant mixing in the reactor vessel is modeled, the accident consequences are mitigated.