The present study developed a series of indicators to assess the electricity generation security of supply under different energy portfolios in Japan in a post-3/11 context. A baseline and four alternative scenarios were designed assuming different shares of fossil fuel and nuclear thermal power and renewables in a 2030 timeframe. The analysis revealed that expanding endogenous energy resources together with a reduction of nuclear power and fossil fuel technologies appears to be a promising strategy to enhance electricity security of supply. Under this strategy imported fossil fuel dependence would decrease to 69.3%, whereas environmental impacts would decline 15-22%, compared to pre-Fukushima levels (baseline scenario). However, an immediate transition to grid-connected renewable energies is not realistic and would increase stress on the system reliability in the short-term, given infrastructure and technical constraints. Investment should be channelised to develop storage and back-up systems, as well as de-centralisation of supply systems to increase energy system resilience and security of supply. (C) 2014 Elsevier Ltd. All rights reserved.