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Comment by Bdennyw | Hacker News Reader

Sadly no mention of thorium or LFTR.

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

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.

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

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.

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.

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

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

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...

The industry is ... skeptical ... of thorium.

Thorium in general, or just liquid fluoride thorium reactors? We know that thorium can work as fuel. We've used thorium as fuel in the past. It can run in Canadian CANDU reactors, or be incorporated into the fuel mix in conventional light water reactors to get drastically improved fuel efficiency, or you can run pebble bed reactors entirely on thorium fuel if you're clever in your ball handling. It's just that uranium is so cheap now that there's not much demand for the increased fuel efficiency that thorium would give -- at least, not until someone does the engineering legwork to get thorium fuel working in existing reactors.

Maybe no one if actively trying to build and get approval for them?

There are probably a few entities doing research, but I could not find any that actually had a schedule for submittion for approval.

First Generation III+ reactor is still being built in Finland. Gen IV (thorium, LFTR etc.) should arrive after 2030.

It seems that there's considerable distance between getting an approval and building one. Areva's EPR-proto has proved that western nuclear industry contractors had forgot (comparable to UK's Trident missile -case) how to actually build nuclear power plants. This has resulted in several years of delays at Olkiluoto, Fi and Flamanville, Fr.

As noted in recent discussion, jet fighter designers will also lose some of their skills when there isn't enough new design work to be done.

"The first license application for the European Pressurized Reactor was made in December 2000. Construction of the power plant commenced in August 2005. The original commissioning date of the reactor was set to May 2009. However, in May 2009 the plant was "at least three and a half years behind schedule and more than 50 percent over-budget". The commissioning deadline has been postponed several times and as of June 2010 operation is set to start in 2013."

- 10-15 years from license application to commissioning!

http://en.wikipedia.org/wiki/Olkiluoto_Nuclear_Power_Plant

"Areva's EPR-proto has proved that western nuclear industry contractors had forgot (comparable to UK's Trident missile -case) how to actually build nuclear power plants."

I really wonder about this: surely the cited concrete problems can't be due to requirements that are entirely unique to building nuclear power plants? (In some case, though, I can well believe it, e.g. the foundation for the reactor, although it ought to be at least a bit like building serious bomb-proof fortifications.)

Have people forgotten how to forge metal? Very possibly, depending on the type and scale needed (I know there are general US issues with our defense industrial base here, then again we just aren't building military artifacts in the old ways anymore (e.g. modular Chobham tank armor vs. cast armor, construction of the B2 ws very different than the B1)), but we need more info than is provided in the source article: http://www.world-nuclear-news.org/NN-Olkiluoto_pipe_welding_...

Which you'll notice the main topic of was a gross failure to properly direct and supervise pipe welding. When you all these three things up, it smells to me like serious supervisory incompetence on the part of the general contractor rather than anything likely to be unique to nuclear engineering.

Of course that could be due to the general contractor getting out of practice, but the concrete and pipe welding it relatively basic stuff (e.g. high quality pipe welding is critical to refinery and chemical plant construction). This sounds more like "out of practice at being serious about their job", which is a sort of institutional rot that can set in when an organization has no real work to do for too long. See e.g. Pournelle's Iron Law of Bureaucracy: http://www.jerrypournelle.com/archives2/archives2mail/mail40...

"Have people forgotten how to forge metal?"

Not entirely related, but there are only three (foundries? forges? - not sure of the noun) capable of creating a one-piece reactor pressure vessel in the entire world, one in Germany, one in Japan, and one in France (I think - there might be two in France and none in Germany).

I can't imagine forging something that big and casting at a foundry wouldn't I think produce what you'd need (maybe, and it would be a cast iron b----, so to speak to do :-). A bit of work with Google came up with this NRC Fact Sheet: http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/pr... which says they "are made of thick steel plates that are welded together" which is what you'd expect. If this was good enough for later 20th century warship armor (which most certainly got put to the ultimate test!) (ADDED:) and submarines (which get put to the test every time they dive) it's good enough for this purpose.

Given that, it wouldn't take too much effort to cobble together what you would need to do it (stuff to hold the work in progress, like the two submarine shipyards we keep alive for the obvious reasons), but it's specialized and low volume enough I'm not be surprised there are only a handful operational in the world right now, and of course post-TMI the US wouldn't have one of them.

Another fun fact: China and Korea are making large reactors without going through Japan Steel. Waiting in line for the heaviest of heavy forgings isn't necessary to create PWR nuclear reactors, even large ones.

The safety requirements are much higher than in the past.

There are lots of problems. For example the control systems are now all digital. Now find THREE INDEPENDTLY designed and programmed control systems, so that these are available redundant and don't fail at the same errors. How many companies are there that can get their stuff certified at the required levels?

Plenty I'm sure, after all aren't there firms doing this work right now (in that the world never stopped building nuclear power plants? I've read that this approach is used by Airbus for dual redundancy.

Given my very limited understanding of the requirements, isn't nuclear reactor control a lot easier than fly-by-wire avionics? And somewhat safer, in that good designs (e.g. not the RMBK) are designed to safely passively fail as Three Mile Island Babcock & Wilcox design quite nicely did in a near worst case accident (about half the core melted with 20 tons of uranium flowing to the bottom).

For Finland there was ONE company capable of doing that, IIRC. They had a hard time finding other companies willing to invest in that area.

Airbus sells many airplanes. Boeing, too. It took a long time to go to fully digital control systems on airplanes.

I don't think any one wants a reactor to passively fail. That's a worst case scenario. If your reactor control system has to fall back to that, then it has no chance. The control system has a) to keep a reactor at all times in safe operation conditions and b) it has to work under failure conditions. If the core melts, then this is an economic loss of billions. The reactor in Finland will cost upwards of 6 billion Euros (last estimates I read were at 5.7 billion Euro). No one would want to have a core melting at such an expensive machine.