There is a heat exchanger that produces steam, but it's not a water cooled reactor. Posted here:
Not a huge, Three Mile Island-type power plant but a new generation of small nuclear reactor about the size of a big spruce tree. Designers say the technology is safe, simple and cheap enough to replace diesel-fired generators as the primary energy source for villages across rural Alaska.
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The Galena design is part of a new generation of small nuclear reactors that can be built in a factory and transported by barge, truck or helicopter. A federal study, funded at Stevens' request and published in May 2001, found they are inherently safe and easy to operate, resistant to sabotage or theft, cost effective and transportable.
Toshiba Corp., the Japanese electronics giant, calls its reactor the 4S system: super-safe, small and simple.
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The reactor core would be constructed and sealed at a factory, then shipped to the site. There it is connected with the other, nonnuclear parts of the power plant to form a steel tube about 70 feet long with the nuclear core welded into the bottom like the eraser in a pencil, Rosinski said. The assembly is then lowered into a concrete housing buried in the ground, making it as immune to attack or theft as a missile in its silo.
The reactor has almost no moving parts and doesn't need an operator. The nuclear reaction is controlled by a reflector that slowly slides over the uranium core and keeps the nuclear fission "critical." If the reflector stops moving, the reactor loses power. If the shield moves too fast, the core "burns" more quickly, yielding the same amount of power but reducing the reactor's life, Rosinski said.
Because of its design and small size, the Toshiba reactor can't overheat or melt down, he said, unlike what happened in the 1986 accident at Chernobyl that killed 30 people and spewed radiation across northern Europe.
The nuclear reaction heats liquid sodium in the upper portion of the reactor assembly. It circulates by convection, eliminating pumps and valves that need maintenance and can cause problems, Rosinski said. The liquid is contained in a separate chamber so it isn't radioactive. Because the reactor assembly is enclosed in a thick steel tube, it will withstand earthquakes and floods, Rosinski said.
"What comes out (of the ground) are two pipes with steam that power a turbine," he said. "You wouldn't even know it's there," except for the steam generator building above it.