“A relatively new kind of reactor design, called a pebble-bed reactor (PBR), has the advantage of being passively safe, which means that if power for cooling systems is lost, then the reactor can safely shut down by itself. Rather than use highly energy-dense fuel rods like many other reactor designs, PBRs use a large number of low-energy-density ‘pebbles’ as fuel, which contain a small amount of uranium surrounded by graphite. This can help slow the nuclear reaction and withstand high temperatures.

This lower energy density means any excess heat will be spread out over all of the pebbles, and so will be easier to transport away using natural cooling processes like conduction and convection, says Zhe Dong at Tsinghua University in China.

While small working prototype reactors have been built in Germany and China, no full-scale PBRs have been shown to work and be passively safe—until now. Dong and his colleagues have demonstrated that the system works with a full-scale nuclear plant, the High-Temperature Gas-Cooled Reactor Pebble-Bed Module (HTR-PM) in Shandong.”

From New Scientist.