Breeder

"Did you have a nice weekend, Joe?" asked a young lady.
"Yeah," Joe replied. "I replaced my gas heating unit with an electric unit."
"Oh, good move!" the young lady replied. "That'll save you a pile of cash."
"Yeah, electricity is practically free and natural gas keeps going up," Joe agreed.
"Makes you wonder how they make electricity so cheap, doesn't it?" asked the young lady.
"Well," answered Joe, savoring this opportunity to display his knowledge, "it's the new liquid metal cooled nuclear reactors. They use the old, spent nuclear reactor fuel and weapons-grade nuclear material and turn it into relatively safe hazardous waste."
"Oh, yeah?"
"Yeah," Joe replied, encouraged by her apparent interest. "These are a new generation off reactors. Very different from the old ones. They're something like 99% efficient and produce so much energy they almost need to give the electricity away."
"Really?" asked the young lady with somewhat fiend enthusiasm.
"Yes," Joe continued, obliviously. "These are breeder reactors that actually use-up nuclear waste. They convert spend nuclear fuel that would be hazardous for thousands and thousands of years to waste that will only be hazardous for a couple of hundred years."
"That's kind of cool," said the young lady. "So, I guess that's why electricity is so cheap."
"Yeah, the government actually pays the power companies to dispose of the old hazardous waste."
"Well, that's neat! All you have to pay for is the cost of replacing your heater."
"That's true. It should pay its self off in five or ten years."

http://en.wikipedia.org/wiki/Liquid_metal_cooled_reactor