Twenty nuclear accidents at the official International Nuclear Event Scale of 4 to 7 have occurred between 1952 and 2011 (Lelieveld et al. 2012). The risk of another major accident during the next 50 years is high and it has been estimated that some 30 million people could be directly affected by such an accident (Lelieveld et al. 2012). The highest risks occur around major metropolises such as New York, Washington, Atlanta, Toronto, Western Europe, Shanghai, Hong Kong, and Tokyo and Osaka. The lessons that have emerged from Chernobyl and Fukushima reveal a range of serious questions that must be answered appropriately, above all for the sake of citizens, but also for the credibility of the nuclear industry, and for framing the ongoing debate over energy alternatives. Because recent models suggest that more than half of released radioactive material from a nuclear disaster would be transported more than 1000 km from the site of release (Lelieveld et al. 2012), these questions are important even for citizens in distant countries. It is in this spirit that we have produced a list of unpleasant questions that have been a cause of concern since we first started conducting research at Chernobyl in 1992, and have grown in urgency since conducting research at Fukushima beginning in 2011.