Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Thorium nuclear reactors: a possible solution of the energy crisis? (video)

youtube.com

Post reply on HN
Print view View original

61–70 of 106 posts

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#61

Post by cheez »

te_chris wrote: post #52
DennisP wrote: post #41

Earlier quoted context omitted.

Thorium reactors should be quite a bit cheaper. Light-water reactors operate at 160 atmospheres of pressure. They need a very strong reactor vessel, which currently can only be forged by a single facility in Japan. They need a large containment dome because if a pipe breaks, that high-pressure water will flash into steam with a thousand times the volume. They use lots of redundant emergency active cooling mechanisms.…

"Misguided government regulation is the main problem, but Sorenson's company plans to get around that by selling to the military first." Sorry but is this subtle irony? My apologies if it's not, I don't know anything about this field. It just seems weird that the military wouldn't be subject to the same regulations that the govt. sets? Or in the US are the military able to ignore some of the regulations around this?

The latter, I'm sure. When you are a war economy, the military rules supreme.

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#62

Post by DennisP »

te_chris wrote: post #52
DennisP wrote: post #41

Earlier quoted context omitted.

Thorium reactors should be quite a bit cheaper. Light-water reactors operate at 160 atmospheres of pressure. They need a very strong reactor vessel, which currently can only be forged by a single facility in Japan. They need a large containment dome because if a pipe breaks, that high-pressure water will flash into steam with a thousand times the volume. They use lots of redundant emergency active cooling mechanisms.…

"Misguided government regulation is the main problem, but Sorenson's company plans to get around that by selling to the military first." Sorry but is this subtle irony? My apologies if it's not, I don't know anything about this field. It just seems weird that the military wouldn't be subject to the same regulations that the govt. sets? Or in the US are the military able to ignore some of the regulations around this?

The NRC has no authority over nuclear aircraft carriers and submarines. The military's stuff is classified, and it does its own regulation.

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#63

Post by jackpirate »

uvdiv wrote: post #57
jackpirate wrote: post #46

Earlier quoted context omitted.

The first reactors were actually heavy water for producing plutonium for nuclear weapons. Light water reactors were developed next because they could still produce plutonium, were cheaper, and could be put on a submarine. But their usefulness on subs was secondary. The USSR built Pb moderated reactors for some Alfa class subs that didn't require anyone working in the engine room. For lots of reasons, this is obviousl…

The first reactors were not heavy-water, but graphite moderated (and light-water cooled). Nazi Germany intended to build heavy-water reactors, but they did not succeed. Pb (actually Pb-Bi eutectic) isn't a moderator, just a coolant. Alfa-class submarines' reactors were fast reactors (no moderator).

I don't know anything about the German bomb program, except that it was pretty unsuccessful. (To be fair, they had people bombing their scientists the whole war.) The heavy water reactors I referred to were from the Manhattan Project. (They did have graphite moderated too, but they weren't as successful I understand.)

You're right that Pb is only the coolant. I got typing too fast.

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#64

Post by fleitz »

Just use CANDU reactors, it will burn raw uranium, and can use the waste product from PWR reactors, just leave the thorium in the raw uranium. It's been working for years, no Yucca mountain, Yucca mountain is a purely US phenomena, it doesn't exist in Canada or France. It's not a new technology, it's 60 years old. All you need is a little heavy water, and in event of a meltdown you just flood the tank with regular water and voila no reactions.

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

Here's the fuel cycle for a CANDU reactor which will support the thorium cycle as well. http://en.wikipedia.org/wiki/File:CANDU_fuel_cycles.jpg

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#65

Post by uvdiv »

jackpirate wrote: post #63
uvdiv wrote: post #57

Earlier quoted context omitted.

The first reactors were not heavy-water, but graphite moderated (and light-water cooled). Nazi Germany intended to build heavy-water reactors, but they did not succeed. Pb (actually Pb-Bi eutectic) isn't a moderator, just a coolant. Alfa-class submarines' reactors were fast reactors (no moderator).

I don't know anything about the German bomb program, except that it was pretty unsuccessful. (To be fair, they had people bombing their scientists the whole war.) The heavy water reactors I referred to were from the Manhattan Project. (They did have graphite moderated too, but they weren't as successful I understand.) You're right that Pb is only the coolant. I got typing too fast.

I believe you've confused something. Almost all plutonium from the Manhattan project (e.g. 'Fat Man') was from graphite-moderated, light-water cooled reactors at Hanford site in Washington, starting with the 'B reactor'.

Plutonium: The First 50 Years (chapter 9)

http://www.doeal.gov/SWEIS/DOEDocuments/004%20DOE-DP-0137%20...

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

The US did not build a heavy-water plutonium production reactor before those at the Savannah River Site (South Carolina), which did not start until 1953. These are all the plutonium production reactors the US has built (ref. DoE): 9 graphite-moderated light-water cooled reactors at Hanford, and 5 heavy-water moderated/heavy-water cooled reactors at Savannah River.

In the Manhattan project, there were also tiny amounts of plutonium sourced from the X-10 reactor at Oak Ridge (also graphite-moderated):

http://en.wikipedia.org/wiki/X-10_Graphite_Reactor

Separately, there was highly-enriched uranium produced at Oak Ridge (Tennessee), which was used in 'Little Boy'.

And, CP-3 was a research heavy-water reactor (Chicago), built in 1944, which was not used for breeding plutonium.

http://en.wikipedia.org/wiki/Chicago_Pile_3

Hope this clears things up...

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#66

Post by DennisP »

zherbert wrote: post #43

I go to school at Boston University and took an Energy class with a Nobel Laureate in physics, Sheldon Glashow, last semester. He spoke in great depth about Thorium reactors, and is very supportive of the technology. One of the main hurdles is that we have poured money into our modern-day reactors, and have constructed hundreds of plants. If we were to switch to thorium, we would have to essentially start from scratc…

Don't switch from uranium. Switch from coal.

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#67

Post by adam-f »

jackpirate wrote: post #44
DennisP wrote: post #30

Earlier quoted context omitted.

It's actually U233 that fissions. The neutrons convert thorium to U233, and when U233 fissions it produces neutrons that convert more thorium. So once you get the reaction started, you don't need an external neutron source. LFTR proponents figure the simplest approach is to just go ahead and use U233 to seed the reaction. The U.S. has one ton of U233, which it currently plans to dispose of.

Short answer: yes, you do need to maintain an external neutron source for Thorium reactors. The advantage of Thorium is that you can maintain the reaction subcritical. That means it is much easier to shut down by simply removing the neutron source. In a critical reactor, you have to physically inject control rods containing a neutron sink (usually Halfnium or Boron). These elements can jam or be ejected under certain…

No no no no.. you don't want to do subcritical particle accelerator reactors. Well, you don't want solid fuel reactors, solid fuel has the same cooling issues as standard uranium, since it's the fission product breakdown that caused the Fukushima accidents (not an initial nuclear excursion, like Chernobyl).

Molten salt can be passively cooled (much better thermal conductivity) and can be moved from core to containment by gravity. Also it expands when its hot, which slows the reaction, and it's chemically stable and doesn't crack like uranium fuel pellets.

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#68

Post by adam-f »

shabble wrote: post #29
DennisP wrote: post #27

Earlier quoted context omitted.

In theory you can, but nobody makes bombs with U233 because it's easier to make bombs in other ways. It seems to me that the real question for proliferation is not "is it theoretically possible to make bombs with this," but rather "if you wanted to make bombs and you had this technology, would you use it to make your bombs, or would you still prefer other methods?"

It's easier to make them other ways at the moment , because U233 isn't common. But popularize and reduce the cost of this cycle, as well as claiming it's "proliferation resistant" and hence suitable for export to non-members of the we-got-nukes club, may well lead to weapons being made out of it.

Still, if you made a u233 device (and I'm thinking it would have to be a dirty bomb, an explosive seems unfeasible), it would difficult to get it to a target since it's so easy to spot the gamma rays.

u235 is still the way to go, since you can just hide it in a lead pipe in a crate of bananas.

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#69

Post by stan_rogers »

api wrote: post #17
jpk wrote: post #11

Earlier quoted context omitted.

My understanding is that building the reactors are significantly more expensive. So until the price of Uranium increases enough to justify the total cost of the Thorium reactors, we won't see many of them outside research settings. The other issue is building a new reactor of any type right now is a giant pain in the ass, which doesn't help either.

CANDU, one of the best uranium designs, has the same problem. It's sort of like inkjet printers. Either it's cheaper up front and more expensive in the long run, or it costs a fortune up front but the ink is cheap.

To be completely honest, though, one of the biggest obstacles to widespread CANDU implementation in the past was that it isn't a breeder.

Re: Thorium nuclear reactors: a possible solution of the energy crisis? (video)

#70

Post by DennisP »

jackpirate wrote: post #44
DennisP wrote: post #30

Earlier quoted context omitted.

It's actually U233 that fissions. The neutrons convert thorium to U233, and when U233 fissions it produces neutrons that convert more thorium. So once you get the reaction started, you don't need an external neutron source. LFTR proponents figure the simplest approach is to just go ahead and use U233 to seed the reaction. The U.S. has one ton of U233, which it currently plans to dispose of.

Short answer: yes, you do need to maintain an external neutron source for Thorium reactors. The advantage of Thorium is that you can maintain the reaction subcritical. That means it is much easier to shut down by simply removing the neutron source. In a critical reactor, you have to physically inject control rods containing a neutron sink (usually Halfnium or Boron). These elements can jam or be ejected under certain…

There are people who advocate subcritical reactors, but that's not how the LFTR works. Fissioning U-233 produces plenty of neutrons to keep a thorium reactor going. See the last couple paragraphs here: http://energyfromthorium.com/2006/04/28/whats-the-difference...
Post reply on HN