After about a 30-year hiatus of construction in the US but not in all involved countries, the designs for an improved water-cooled nuclear reactor will hopefully be developed by a consortium of nuclear reactor builders and users under an agreement with the US Department of Energy (DOE) and review by the Nuclear Regulatory Commission (NRC). The construction of high-temperature, helium-cooled pebble-bed or prismatic reactors may herald the entry of new, safer, and less costly types of reactors to replace the water-cooled reactors of the past and current types. Nuclear breeder reactors hold the promise of limitless energy supplies without the use of fossil fuels or renewables at acceptable costs but this development program has been stalled periodically, especially in the US, when abundant low-cost uranium sources were added to the supply side.(C) 2007 Elsevier Ltd. All rights reserved.