Pebble Bed returns?

Pebble Bed Advanced High Temperature Reactor at UC Berkeley – low cost nuclear?

Well, I haven't heard anything about the South African pebble bed reactor development lately. (Probably, I learn right now, because it has definitely gone belly up.)

Yet a new type of pebble bed reactor is discussed at Brave New Climate: one that uses molten salts as a coolant. Reporting on a visit to UC Berkeley:

So, back to Per’s lab. He has various engineering models set up to test movement of TRISO pebble fuel through a fluoride salt coolant, whereby the pebbles are inserted in the inlet pipes and rise up through the reactor module over time, and then are put back through 5 or 6 times. This allows for very high burnup — exceeding 50 %, high power density due to the heat capacity of the liquid salt, and high temperatures thanks to the durability of the pebbles. This is a big (potential) advantage over the current Pebble Bed Modular Reactor technology (PBMR), because in that design, the gas coolant has a very low power density. He’s flipped the problem on its head. The reactor also has various inherent safety design features, such as control rods that sink naturally in response to elevated coolant temperature, thereby passively regulating reactivity. Very safe!

Of course, this does not sound as modular as the South African design was intended to be, but it is still being explored as means of making cheaper nuclear designs than the current designs. (The article explains that the cost of new nuclear is still providing prohibitive for its expansion in the US.)

So it's a case of the pebble bed is dead...long live the pebble bed!