This work seeks to evaluate overnight construction costs (OCC) and lead-time escalation of nuclear power construction projects from 1955 to 2016. To this end, a comprehensive database of commercial Light Water Reactors (LWR) was developed and a statistical analysis was conducted. Findings reveal a significant delay in lead-time, especially for the last generation reactors constructed from 2010s, with 3/4 of the sample showing significant construction delays. This results in an escalation of capital costs rather than in a decline. Average OCC of newer reactors is 60% higher than the ones implemented in the earlier stages of the nuclear era. This suggests a discontinuity of the learning curve for both OCC and lead-time, which threats the market and financial sustainability of current and future nuclear energy projects. Although this is a general trend, this discontinuity is country specific and, thus, induced by national policies and regulatory frameworks. Therefore, the role of nuclear technology as an alternative to cope with the need for a decarbonisation of the power sector must be better evaluated, taking into account the real cost impacts of nuclear technology implementation.