[Confusion]

No mention of pebble bed reactors[1] either, which is a shame, because AFAIK they are still the only ones that cannot melt down. They produce less energy the hotter they get and one can design them to, for instance, never exceed 1800K. If the cooling system fails, the system simply reaches a steady state at that temperature. There is thorium variety of this reactor.

[1] http://en.wikipedia.org/wiki/Pebble_bed_reactor

[lispm]

Funky, the english Wikipedia page. It says that the German pebble bed reactor was abandoned due to 'political and economic' reasons.

The truth can be read in the German version of the article, it simply did not work problem free. It is also mentioned further down in the English article. The German article about this specific reactor, the THTR-300, goes into detail.

The pebbles were breaking. The concrete got too hot. The reactor got too hot in its center. Taking out pebbles could only be done when he reactor was running with reduced power. It also had an accident where the reactor was leaking radioactivity.

All in all the handling of the pebbles had many ugly surprises for pebble bed reactor designers. They were breaking at a rate of 1000 higher than expected.

[pjscott]

The German pebble-bed was built in 1983 and shut down in 1989. Pebble bed reactor designers have had 21 years to improve on that design, and they've not been idle. All real nuclear reactors have problems before you've had time to work out the bugs in the design. They're big, complicated machines, and they have to meet some pretty stringent engineering specs.

The German THTR-300 was the first attempt to build a full-scale pebble bed reactor, after they'd run just one smaller research reactor. Problems with the design are to be expected. That's not an indictment of pebble bed reactor designs; that's just how nuclear engineering works. I'm glad that the pebble bed guys are finally picking themselves off the floor and continuing on with the Chinese HTR-PM reactors, which were designed to avoid the problems which plagued the THTR-300.

[lispm]

This German study (2008) from Jülich (!) was quite critical about the whole concept:

http://juwel.fz-juelich.de:8080/dspace/bitstream/2128/3136/1...

[JanezStupar]

Off course they are mentioned - its the High-Temperature gas-reactor or "Next Generation Nuclear Plant". It is mentioned that a pebble bead and prismatic designs exist.

However - I am also missing LFTR - which BTW is also "unmeltable" and cannot go supercritical.

[Confusion]

I stand corrected; I missed the bit about the pebble-bed variety and thought they only mentioned the prismatic one.

[pjscott]

And China is building some right now. The HTR-PM pebble bed reactor is actually two reactors connected to a single steam turbine, for a total of 210 MWe. They're building one of these two-reactor modules now, and they're planning another 18 reactors on that same site once they've got the kinks worked out and the factories set up to start really cranking them out. More on the current status and technical and economic details here:

http://nextbigfuture.com/2010/02/current-status-and-technica...