As a response to economic growth, electric power utilities installed many electric power facilities to meet power demand. However, these facilities have aged and should be replaced in the near future. Moreover, after the Great East Japan Earthquake, significant power flow changes in power system would likely to happen. Therefore, for electric power facilities planning, it is necessary to solve such power flow problems. In this paper, we assume a protracted loss of generation capabilities in a nuclear power plant and examine the resulting load changes. We propose the use of series capacitors on nonheavily loaded lines to alleviate load differences among transmission lines. We also propose the concept of mitigation flow sensitivity (MFS). By installing series capacitors at effective locations and determining compensation amounts by prioritizing the MFS, we can solve the power flow problems. We carry out simulations to confirm the validity of the proposed method.