In the next 50 years, unless an alternative is found, energy demand and production will be increasing, and this will contribute to global warming through excessive release of more harmful greenhouse gas emissions into the atmosphere. If the energy is not created from Nuclear Power Plants (NPPs) or renewables limitations are not surpassed, new millions of tons of carbon emissions per year will be produced through combustion of coal and natural gas and the global temperature will increase by 2 degrees Celsius. On another hand, scientists project that climate change will increase the frequency of heavy rainstorms, putting many communities at risk of devastation from floods. Extreme rain, fast mountains ice melting, a dam rupture or embankment, or even a dam failure can flush with river water the floodplain. Some of the floods develop slowly and give a chance for reaction and even evacuation; others come so fast that there is no time for warning and preparation. These flash floods can also damage critical infrastructure like NPPs as the plants are usually built close to water bodies, for the sake of cooling. The site selection and the design of the plant take into account the worst case flooding scenarios as well as other possible natural disasters and, more recently, the possible effects of climate change. As a result, all the buildings with safety-related equipment are situated on high enough platforms so that they stand above underwater areas in case of inundating events. Although engineered countermeasures have been built, in the past, some buildings and back-up equipment have been sited too low, so that they are vulnerable to flood. In March 2011 at the Fukushima Daiichi NPP an earthquake shut down the three units and 14 meters high Tsunami coming ashore cut power supply and damaged seriously the back-up diesel generators. The reactor couldn't continue to cold shutdown status and the other units suffered flooding. The Japanese NPP catastrophe was a reminder for the European Union to carry out a complete upto- date assessment of the current European nuclear reactors safety especially in respect of a combination of extreme external hazards. In this paper I will focus on the future of the existing and forthcoming NPPs located at the second biggest European River- The Danube, observing the international and regional legal instruments and institutions for nuclear safety and flood protection cooperation. I will use Bulgarian Kozloduy NPP as an example for the study of the IAEA Safety Standards especially in the process of safety assessment and site evaluation, done during the European stress test in regards of floods. Finally, I will address recommendations and conclusions.