Data transfer between codes TRANSURANUS NEUTRONICS ALHR Tfuel THERMAL- HYDRAULICS αcoolant-clad Tcooant In the frame of a PhD at HZDR, the reactor dynamics code DYN3D has been coupled at assembly level in order to describe the fuel behavior in more detail. In the coupling, DYN3D provides process time, time-dependent rod power and thermal hydraulics conditions to the TRANSURANUS fuel rod performance code, which transfers parameters like fuel temperature and cladding temperature back to DYN3D. Results of the coupled code system have been analysed for the reactivity transient scenario [1], initiated by control rod ejection, as well as for a boron dilution accident [2]. The numerical performance for DYN3D-TRANSURANUS was shown to be fast and stable. The coupled code system could therefore improve the assessment of safety criteria, at a reasonable computational cost. References: [1] L. Holt, U. Rohde,M. Seidl, A. Schubert, P. Van Uffelen, R. Macián-Juan, Annals of Nuclear Energy 84 (2015) 73–85 [2] L. Holt, U. Rohde, S. Kliem, S. Baier, M. Seidl, P. Van Uffelen, R. Macián-Juan, Nuclear Engineering and Design 297 (2016) 32–43 pcoolant Tclad

Data transfer between codes TRANSURANUS NEUTRONICS ALHR Tfuel THERMAL- HYDRAULICS αcoolant-clad Tcooant As first application the reactor dynamics code DYN3D was coupled at assembly level in order to describe the fuel behavior in more detail. In the coupling, DYN3D provides process time, time-dependent rod power and thermal hydraulics conditions to TRANSURANUS, which in case of the two-way coupling approach transfers parameters like fuel temperature and cladding temperature back to DYN3D. Results of the coupled code system are presented for the reactivity transient scenario, initiated by control rod ejection. More precisely, the two-way coupling approach systematically calculates higher maximum values for the node fuel enthalpy. These differences can be explained thanks to the greater detail in fuel behavior modeling. The numerical performance for DYN3D-TRANSURANUS was proved to be fast and stable. The coupled code system can therefore improve the assessment of safety criteria, at a reasonable computational cost. pcoolant Tclad