In Nuclear Power, Size Matters

PerlJedi writes "Most nations with nuclear power capabilities have been re-assessing the risk/benefit of nuclear power reactors following the Fukushima plant melt down, a newly released study suggests the U.S. should expand its nuclear power production using 'Small Modular Reactors'. 'The reports assessed the economic feasibility [PDF] of classical, gigawatt-scale reactors and the possible new generation of modular reactors. The latter would have a generating capacity of 600 megawatts or less, would be factory-built as modular components, and then shipped to their desired location for assembly.'"

Comments

Re:right idea - Wrong fuel

[denis-The-menace]

/. ate my link
http://thoriumremix.com/2011/

Citation?

[Anonymous Coward]

I work as a consultant for electricity planning, and I have *never* seen a single survey which shows that folks who live near a nuclear plant are in favor of new units being built at the site. Not a single survey. Not even for Vogtle units 3 and 4, being built right now next to units 1 and 2, located on the Georgia-South Carolina line... a place where I'd expect a more favorable response than most.

If you've got one, I'd love to see it.

Re:right idea - Wrong fuel

[vlm]

Theres a whopping big wiki article that tries a little too hard to be "balanced" when in all fairness Th is a PITA fuel, that kinda sucks.

Its only good for non-proliferation from a distance. Up close its worse. You need to boot up with a slug of Pu because there are no fissile Th isotopes. So no one ever builds "a Th reactor" they build a "bomb grade Pu reactor" surrounded with a Th shell that eventually can breed itself into reacting, hopefully your breeding plan curve matches your electrical demand curve.

Its only good for non-proliferation if you define proliferation as current designs. Historically plenty of U233 bombs were blown and research done. No you cannot make a current model US B61 out of stuff from a Th reactor. Yes, you can make something almost as good as a B61 that is U233 based using what comes out of a Th reactor. It in no way prevents proliferation merely makes it a slightly more involved research project (slightly!)

In a way, not being useful for proliferation dooms Th. The US and Russia and China and god only knows who else (Iran?) are still going to need U based reactors so now you've gotta run both technologies... Why not just run one? And that one's gotta be U, at this time. So trying to push Th means your sales will be pitiful because you can only sell to 3rd world and not much else.

Plus it gives the non-proliferating Th owners experience in plant operation which they can transition to new/secret U plants of their own anyway, its like bootstrapping proliferation not preventing it.

Anyone who says Th = nonproliferation is either misinformed or being paid or trolling.

Its an unholy PITA to recycle due to hard gammas, or you can have agony when disposing. Its waste stream is just "worse" than a traditional reactor.

Its harder to run, more neutron poisons like Pa build up.

To be economical, you just have to burnup into the ground, which is kind of like saying a F-350 has a lower lifetime environmental cost IF you can get it to survive 600K miles. Its... ambitious. You don't achieve high burnup by just wishing, its difficult, dangerous if you have cladding failures, and expensive. Otherwise the prius wins again for overall lifetime costs.

Its interesting to learn about, good to learn about, but it shows good engineering judgment to avoid a Th design.

You obviously didn't watch the video...

[andersen]

They are NOT at suggesting using solid thorium and making fuel rods. That would indeed be truly stupid.

The LFTR uses thorium dissolved in molten floride salt. It is proven tech, since the US government
built one back in the late 60s and ran it for 5 years -- with 1.5 years at full power...

Watch the video http://thoriumremix.com/2011/
then and only then can you properly comment on thorium....

Re:You obviously didn't watch the video...

[BlueParrot]

The LFTR uses thorium dissolved in molten floride salt. It is proven tech, since the US government
built one back in the late 60s and ran it for 5 years -- with 1.5 years at full power...

The devil is in the details.

While it is indeed possible to build an LFTR, that old bugger called economics tends to come and mess things up.

First of all you need a larger amount of fissile materials since the molten salt transports it out of the core. and around the entire primary loop. Secondly, as with sodium, you need to have a secondary loop to make things safe. Then there's the hydrolysis that can occur at low temperatures, which means you have to keep the salt molten. If the reactor has problems, that may involve drawing power from the grid. The reprocessing technologies kinda work, but are unproven at large scale, and nobody has an idea what the cost will be for a large reactor. They also imply building reprocessing tech for every single plant, which increases capital costs.

Then there is the startup material. Natural uranium is not good enough, so you either need to breed U-233 in a different reactor ( proliferation concern ) , use highly enriched U-235 ( proliferation concern, expensive ) , or startup on plutonium. Now plutonium in a thermal spectrum leads to accumulation of Curium, which is a troublesome waste product that cannot be efficiently destroyed in a thermal reactor.

Add in that while Thorium and Uranium dissolves easily in fluoride salts, plutonium and the other actinides do not. In fact, even at high temperatures with a completely pure salt, the solubility of Pu fluorides is just a few percent. The molten salt reactor experiments got around these issues by using a very exotic salt. Beryllium and Lithium fluorides, with the lithium enriched in Li-7. Now, beryllium is highly toxic, expensive and difficult to work with. It's such a pain that the US and UK considered developing new nuclear warheads that did not use it, even though it is the best lightweight neutron reflector there is. Enriched lithium-7 is a different problem in itself, and even if 99% pure, you will get quite a bit of tritium when it is exposed to neutrons. Perhaps not more than in a CANDU reactor, but all tritium control systems ever designed are made for water coolant.

Then is the issue of in-core materials. The molten salt reactor developed by the US dealt with damage to in-core materials by replacing the graphite core materials frequently. Not only is this expensive, but it's not very fun to handle radioactively contaminated graphite. It is hard to reprocess since it forms organic compounds and is difficult to dissolve in nitric acid. Pyro-processing by electro-refining and similar is also poorly suited for graphite. This is one of the reasons why the pebble bed reactors are usually seen as "once through". Nobody has come up with a practical way to deal with the graphite. Since the material will be in direct contact with the fuel salt, it will likely adsorb quite a bit of contaminants.

Plateout on heat exchangers is another issue. The noble metals have poor solubility in fluoride salts, so unless a very potent ( i.e expensive ) reprocessing system is able to get rid of them quickly, they will plate out on the cold parts of the reactor, which is usually the heat exchangers. A suggested solution is to use graphite-based heat exchangers, which has its own spectrum of development issues and research needs.

I'm not saying molten salt reactors can never become a good idea. I'm just saying that in comparison to the number of issues that need to be resolved to make them practical for a power plant, they are extremely hyped.