Refurbishment and long-term operation (LTO) of existing nuclear power plants (NPPs) today are crucial to the competitiveness of the nuclear industry in OECD countries as existing nuclear power plants produce baseload power at a reliable cost. A number of nuclear power plants, most notably 73 units in the United States (up to 2012), have been granted lifetime extensions of up to 60 years, a development that is being keenly watched in other OECD countries. In many of these (e.g. France, Switzerland), there is no legal end to the operating licence, but continued operation is based on the outcomes of periodic safety reviews. This study analyses technical and economic data on the upgrade and lifetime extension experience in OECD countries. A multi-criteria assessment methodology is used considering various factors and parameters reflecting current and future financial conditions of operation, political and regulatory risks, the state of the plants’ equipment and the general role of nuclear power in the country’s energy policy. The report shows that long-term operation of nuclear power plants has significant economic advantages for most utilities envisaging LTO programmes. In most cases, the continued operation of NPPs for at least ten more years is profitable even taking into account the additional costs of post-Fukushima modifications, and remains cost-effective compared to alternative replacement sources.