Hydrogen generation on a large scale will be required to power the emerging hydrogen economy without emitting large amounts of carbon dioxide into the atmosphere. All large-scale hydrogen production facilities currently in operation use processes such as steam methane reforming or partial oxidation of heavy hydrocarbons, which emit large amounts of carbon dioxide. Atomic Energy of Canada Ltd. (AECL) is studying several process options for large-scale production of hydrogen without emitting carbon dioxide. One of these options is to produce hydrogen via steam electrolysis, where the heat and electricity are produced by nuclear reactors. This paper investigates the technical issues and economics of hydrogen production by integrating a steam electrolysis system with the Advanced CANDU Reactor ACR-1000. The overall thermal-to-hydrogen efficiency of the combined ACR-1000 and steam electrolysis process is 33-34% compared to about 27% for conventional water electrolysis. The heat recovered from the steam electrolysis loop is used to provide heat at appropriate locations in the electricity generation cycle. Copyright (C) 2007 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.