By 2013, utilities will be able to order a nuclear power generator and have it trucked to their site. Via Instapundit:

 The Hyperion Power Generation uranium hydride reactor will weigh fifteen to 20 tons, depending on whether you’re measuring just the reactor itself or the cask—the container that we ship it in—as well. It was specifically designed to fit on the back of a flatbed truck because most of our customers are not going to have rail. It’s about a meter-and-a-half across and about 2 meters tall. It will generate 27-30 Megawatts of electrical power from 70 MW of thermal power.

This means 0.5 to 0.75 tons per MWe for the nuclear reactor. The steam turbine to convert the power is counted separately. Using a lot less material (including 10 to 20 times greater efficiency with the Uranium fuel) means that the uranium hydride reactor can be scaled to provide more power. Eventual use of advanced thermoelectrics instead of steam turbines would mean that the weight of the reactor and power conversion would be less than one ton per MWe.