Further information on the Toshiba mini-reactor can be found here and here

A small-scale design developed by Toshiba Corporation in cooperation with Japan’s Central Research Institute of Electric Power Industry (CRIEPI) and funded by the Japan Atomic Energy Research Institute (JAERI) is the 5 MWt, 200 kWe Rapid-L, using lithium-6 (a liquid neutron poison) as a control medium. It would have 2700 fuel pins of 40-50% enriched uranium nitride with 2600°C melting point integrated into a disposable cartridge. The reactivity control system is passive, using lithium expansion modules (LEM) which give burnup compensation, partial load operation as well as negative reactivity feedback. As the reactor temperature rises, the lithium expands into the core, displacing an inert gas. Other kinds of lithium modules, also integrated into the fuel cartridge, shut down and start up the nuclear reactor. Cooling is by molten sodium, and with the LEM control system, reactor power is proportional to primary coolant flow rate. Refuelling would be every 10 years in an inert gas environment. Operation would require no skill, due to the inherent safety design features. The whole plant would be about 6.5 meters high and 2 meters in diameter.

For much more, see Brian Wang’s postings here and here.
I can see why people might think it’s a hoax. Toshiba’s official site has got nothing on it. Nevertheless, it would seem to be legit.
UPDATE: Title suggested by M. Simon, who has more.
(Bumped to the top by Eric, in a fit of Christmas Eve altruism.)