Simulation of Phenix control rod withdrawal experiments with SIMMER-IV

The "end-of-life" tests performed in the PHENIX reactor in 2009, in particular the Control Rod (CR) withdrawal experiments provide an excellent opportunity for validation and verification of the reactor physics computer codes and modelling approaches. SIMMER-IV, a modern three-dimensional reactor safety code, has been recently employed at KIT for simulating these experiments in the framework of a benchmark exercise organized under the IAEA project. In this paper, we report and discuss main results obtained with SIMMER at KIT. The reactor reactivity, power and neutron flux distributions calculated with SIMMER-IV are in good agreement with advanced neutronics codes, such as ERANOS, while the CR reactivity worth is overestimated due to neglecting heterogeneity effects. We show that SIMMER neutronics model can be improved by employing a correction that is based on the results of cell calculations performed with ERANOS. The study confirms that the 3D SIMMER-IV code can accurately predict major fast reactor neutronics parameters, provided that a special treatment is employed for CR modelling. (author)