A NUCLEAR reactor designed to generate power in the basement of an apartment
block is being developed in Japan. In the past few months government-backed
researchers have been testing a fail-safe mechanism for the reactor, which will
close down automatically if it overheats.
The Rapid-L reactor was conceived as a powerhouse for colonies on the Moon.
But at 6 metres high and only 2 metres wide this 200-kilowatt reactor could
relatively easily fit into the basement of an office building or apartment
block, where it would have to be housed in a solid containment building.
鈥淚n the future it will be quite difficult to construct further large nuclear
power plants because of site restrictions,鈥� says Mitsuru Kambe, head of the
research team at Japan鈥檚 Central Research Institute of Electrical Power Industry
(CRIEPI). 鈥淭o relieve peak loads in the near future, I believe small, modular
reactors located in urban areas such as Tokyo Bay will be effective,鈥� he says.
Kambe鈥檚 research is being financed by the Japan鈥檚 Atomic Energy Research
Institute.
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Unlike normal nuclear reactors, the Rapid-L has no control rods to regulate
the reaction. Instead, it uses reservoirs of molten lithium-6鈥攁n isotope
that is effective at absorbing neutrons. The reservoirs are connected to a
vertical tube that runs through the reactor core. During normal operation the
tube contains an inert gas. But as the temperature of the reactor rises, the
liquid lithium expands, compressing the inert gas and entering the core to
absorb neutrons and slow down the reaction.
The lithium acts as a liquid control rod. And unlike solid control rods,
which have to be inserted mechanically, the liquid expands naturally when the
core gets warm.
The Rapid-L uses the same principle to start up and close down the reaction.
The reactor would be cooled by molten sodium and run at about 530 掳C.
Kambe鈥檚 main concern now is to test the fail-safe system鈥檚 long-term
durability.
The research 鈥渋s part of the effort being made in the US and in Japan to
develop reactors which do not need hardware to keep them safe,鈥� says John Gittus
of the University of Plymouth. 鈥淩apid power plants could be used in developing
countries where remote regions cannot be conveniently connected to the main
grid,鈥� says Kambe.
鈥淭he success of such a reactor depends on the acceptance of the public, the
electricity utilities and the government,鈥� Kambe admits. But Malcolm Grimston, a
nuclear expert at the Royal Institute of International Affairs, is sceptical
that the Japanese people could be persuaded of the reactor鈥檚 safety.
鈥淭here鈥檚 nothing wrong with the concept,鈥� says Grimston. 鈥淏ut if the Japanese
public won鈥檛 now accept big reactors for safety reasons, then you have to wonder
what the response would be building lots of small reactors in the middle of
肠颈迟颈别蝉.鈥�
