Ever shrinking device structures result in an increased susceptibility of modern embedded systems to radiation and temperature-dependent aging effects. This work introduces a runtime placement algorithm for dynamically reconfigurable systems that have to meet varying safety requirements. The algorithm first allocates replicas of modules to cope with soft-errors and meet the safety-level of the module and then places the modules onto the FPGA in such a way that the stress, and therefore aging, is minimized. For the replica allocation, a lifetime analysis is employed to predict the reliability of a module depending on its sensitive configuration bits and the expected runtime of the module. Moreover, the temperature profile of each active module is utilized to predict the degradation of each part of the reconfigurable area. The presented algorithm then equally distributes active modules to minimize the degradation effects while respecting placement constraints that arise from the need for majority voting between the different replicas of a module. A case study gives evidence of the capability of the proposed online placing algorithm to harden a system against radiation effects and meet safety constraints while extending the overall lifetime of the reconfigurable device by minimizing stress.