Miniature nuclear reactors that can run without human intervention for up to a decade will be available within five years, according to the company tasked with building them. Each one will be smaller than an average garden shed and will generate power for 20,000 homes.

The power plants will be almost impossible to attack or steal as they will be encased in concrete and buried underground. They will contain no weapons-grade material.

The reactors will cost up to $25 million (£16.5 million) each but are expected to provide cheaper energy than traditional sources such as coal and gas. As a result, the reactors could provide a crucial new energy source for developing countries or even for remote military installations. They will be delivered on the back of a lorry and will have no moving parts.

The US Government has licensed the technology to Hyperion Power Generation, a New Mexico-based company that has already started to take orders for the small power plants and aims to mass produce them by 2013.

John Deal, the company's chief executive, said: “Our goal is to produce power and electricity anywhere in the world for less than ten cents per kilowatt hour."

Figures from April this year show that the average cost of producing residential electricity in the US was 11 cents per kilowatt hour.

Mr Deal said that the new reactors would produce energy for seven to ten years before they had to be refuelled. They will produce only “a cricket ball-sized amount of waste”, he said, which would be easier to deal with than the quantities of waste created by large reactors.

The first firm order came from TES, a Czech infrastructure company specialising in water and power plants. More orders have arrived from around the world, including the Cayman Islands, Panama, the Bahamas and countries in Africa.

Mr Deal said the reactor is expected to meet diverse safety and regulatory requirements throughout the world.

“It can’t melt down,” he said. “If it goes above a set temperature point, the nuclear reactivity will on its own slow down. That’s chemistry, not us.”

The reactors will be buried to reduce the chance of their being attacked, and to eliminate the aesthetic impact on the communities that they power.

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