Japan has recently been urged to implement measures to increase utility factors for nuclear power plants in order to address energy security and greenhouse gas emission cuts. The average utility factor for Japan's nuclear power plants in 2009 rose from 58.0% in 2008 to 64.7%, still below levels in other major nuclear power generation countries including South Korea and the United States. Some major foreign nuclear power generation countries have kept their utility factors for nuclear plants at high levels at or above 90% since 1990, while others including the United States and South Korea have raised their respective factors since 2000 following the 1990s when their factors were close to the Japanese level. The latter group made ambitious efforts to raise these factors. Specifically, the United States has shortened planned outage time for periodic maintenance and repairs of nuclear power plants year by year as the nuclear industry and the Nuclear Regulatory Commission have tried to take advantage of risk information for optimizing instrument-by-instrument inspection frequencies and for expanding the scope for preventive maintenance during operation (PMO). Unplanned outage time to solve nuclear plant instrument issue has also been shortened substantially thanks to the reduction of the trouble incidence rate and shorter repair and restart times. The United States has also tried to lengthen operational cycle periods, adopting 18-to-24-month cycles for many plants. In a bid to shorten plant outage time, South Korea has promoted not only the improvement of operational skills and the introduction of sophisticated instruments but also the enhancement of maintenance know-how including the reform of maintenance and repair processes and the improvement of inspection work steps. Overseas cases for the restart of nuclear plant operations from an unplanned plant outage include those in multiple countries in which thorough investigations into minor troubles or measures for their future prevention were not necessarily required for restarting plants. As far as our analysis generally indicates, local governments are not authorized to examine nuclear plant safety in foreign countries. An apparent dominant view in foreign countries is that it would be reasonable to utilize infrastructure as much as possible once safety regulation authorities conclude that a plant restart would have no safety problems. As existing nuclear power plants have been required to be effectively utilized under the top priority on safety, some countries have continuously achieved high utility factors for nuclear plants, between 85% and 95% over 10 to 20 years while meeting safety standards at the same level as in Japan. In considering specific measures to effectively utilize existing nuclear reactors, Japan should take full account of these overseas efforts and promote discussions on overall Japanese nuclear energy and safety approaches.