Since Fukushima many are calling for a shutdown of nuclear power plants. To see whether such a shutdown would reduce the risks for health and environment, the external costs of nuclear electricity are compared with alternatives that could replace it. The frequency of catastrophic nuclear accidents is based on the historical record, about one in 25 years for the plants built to date, an order of magnitude higher than the safety goals of the U.S. Nuclear Regulatory Commission. Impacts similar to Chernobyl and Fukushima are assumed to estimate the cost. A detailed comparison is presented with wind as alternative with the lowest external cost. The variability of wind necessitates augmentation by other sources, primarily fossil fuels, because storage at the required scale is in most regions too expensive. The external costs of natural gas combined cycle are taken as 0.6 epsilon cent/kWh due to health effects of air pollution and 1.25 epsilon cent/kWh due to greenhouse gases (at 25 epsilon/tco(2)eq) for the central estimate, but a wide range of different parameters is also considered, both for nuclear and for the alternatives. Although the central estimate of external costs of the wind-based alternative is higher than that of nuclear, the uncertainty ranges overlap. (C) 2013 Elsevier Ltd. All rights reserved.