Abstract The evolutionary multi-physics tool developed at the Karlsruhe Institute of Technology is the homogeneous pin-by-pin reactor simulator DYNSUB, an internal coupling of the 3D neutron kinetics code DYN3D developed by Helmholtz Zentrum Dresden Rossendorf and the in-house sub-channel code SUBCHANFLOW. The ultimate goal of the on-going efforts concerning DYNSUB is to provide a cost-effective improved description of light water reactor core behavior with pin-by-pin resolution for both static and transient safety relevant scenarios. A cost-effective computer code is defined to be executable on commodity computing clusters which users/customers commonly have access to. Efforts undertaken to improve DYNSUB’s numerical performance and parallelize the code system are presented in this work. Moreover, the coupled code system has been extended in terms of fuel pin level homogenization corrections and flexible mapping schemes. After optimization and extension DYNSUB is successfully applied to study the OECD/NEA and U.S. NRC PWR MOX/UO 2 core transient benchmark with both fuel assembly/channel and pin level/sub-channel model resolution. Even though further improvements in terms of numerical performance and accuracy of physical models are required, the applicability of DYNSUB pin-by-pin simulations for light water reactor safety analysis is proven in principle in this work.