Japan developing micro nuclear
Reactor for apartment blocks

PARIS, Aug 22 (AFP) - Japan is developing a tiny nuclear reactor designed to generate power in the basement of an apartment block, despite wide-spread public concern over the country's nuclear safety record, New Scientist says. The 200-kilowatt micro-reactor, Rapid-L, measures just six metres (20 feet) high and two metres (6.5 feet) wide and was initially conceived as a plug-and-play source of power for lunar colonies. Although colonisation schemes have long been shelved, scientists at Japan's Central Research Institute of Electrical Power Industry (CRIEPI) have revived plans for the Rapid-L, believing it could be a handy source of power for an office building or apartment block, the report says. It would be located in the building's basement, surrounded by a solid containment structure for safety reasons.

"In the future it will be quite difficult to construct further large nuclear power plants because of site restrictions," Mitsuru Kambe, head of the research team, told the British science weekly. "To relieve peak loads in the near future, I believe small, modular reactors located in urban areas such as Tokyo Bay will be effective," he said.

Kambe added, however: "The success of such a reactor depends on the acceptance of the public, the electricity utilities and the government." In the past few months, Kambe's team have been testing a fail-safe mechanism to close the reactor down in the event of overheating, the report says in next Saturday's issue of New Scientist.

The work is being financed by the Japan's Atomic Energy Research Institute. Unlike con-ventional reactors, the Rapid-L would have no control rods to regulate the nuclear reaction, the goal being to remove a mechanical source of potential malfunction.

Instead, it would use reservoirs of molten lithium-6, an isotope that is effective at absor-bing 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 reactor would run at about 530 C (986 F), cooled by liquid sodium.

Malcolm Grimston, a nuclear expert at the Royal Institute of International Affairs, doubted whether the Japanese public could be persuaded that the reactor was safe, given a string of incidents at large nuclear plants in recent years. In the worst case, two workers died at a uranium processing plant in Tokaimura in 1999, more than 400 other people were exposed to radiation and at least 300,000 people were forced to shelter indoors for more than a day.

"There's nothing wrong with the (Rapid-L) concept," Grimston told New Scientist. "But if the Japanese public won't 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 cities."

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