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Fact-check: Five claims about thorium made by Andrew Yang

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Re: Fact-check: Five claims about thorium made by Andrew Yang

#91

Post by pfdietz »

acidburnNSA wrote: post #15
DennisP wrote: post #9

> similar radioactivity at 100 years to uranium-plutonium fuel cycles, and actually has higher waste radioactivity at 100,000 years At 100 years your radioactivity is still dominated by fission products, which are the same in either reactor. At 100,000 years the radioactivity is minuscule with any reactor. But what you don't have with thorium or fast uranium reactors is a lot of transuranic waste, like plutonium. Tha…

A few points: * Uranium-Plutonium fuel in a closed cycle can burn all the transuranics and have very low radiotoxicity waste as well. * Molten salt fuels are 10x less dense than typical solid fuels, implying an increase in waste volume. They're also water soluble and frequently liquid. This complicates waste disposal and transport. Not terribly, but still. A good summary reference on radiotoxicity vs. reprocessing is…

A uranium-plutonium fuel in a closed cycle can do that if you have fast reactors. Thermal reactors, no. And the higher transuranics become increasingly difficult to burn, since the delayed neutron fraction goes way down. A reactor burning higher transuranics will be right on the knife edge of prompt supercriticality.

Re: Fact-check: Five claims about thorium made by Andrew Yang

#92

Post by pfdietz »

HorstG wrote: post #4
Glyptodon wrote: post #3

Several things in this FAQ are frequently contradicted, which I'm not sure what to make of.

They are not wrong, but also not right in all scenarios. Truth very much depends on the reactor design. Thorium is often associated with Gen4 reactors which are responsible for the claims of superior safety. Not much, but some of the safety benefit comes from thorium. Similar for the claim of less waste: Some reactors have better neutron economy, burning their own waste down to more shortlived and therefore "better"…

The FRONT END of the fuel cost is lower. But in a molten salt reactor with fuel dissolved in the salt, reprocessing is not optional! The fission products have to be removed from the fuel salt at some point (reprocessing) because the salt is expensive (especially FLiBe). So the back end of the fuel cycle will impose costs that do not exist with today's once through fuel cycles.

Re: Fact-check: Five claims about thorium made by Andrew Yang

#93

Post by tabtab »

sjwright wrote: post #10
erentz wrote: post #5

Yang is to be credited for stating he is open to all possible solutions to the climate crisis, and rightly pointing out that with a crisis of this magnitude no solutions should be taken off the table at this point. Something other candidates are reluctant to do when it comes to the topic of nuclear energy. He shouldn’t be expected to be an expert in the nuances of the technology or fuels. This should always be left t…

Exactly. The takeaway should be that Yang is approaching this issue from a position of technical merit and not on an irrational emotional basis like most others. This is to his credit. Properly technocratic leadership is rare in the USA and it's beyond time for them to experiment with it. In my opinion the analysis linked to from HN is laughably flawed. It's not exactly wrong, but it's so terse and reductive that it…

Re: Yang is approaching this issue from a position of technical merit and not on an irrational emotional basis like most others.

Unfortunately, politics is not rational. Energy sources that kill slowly but gradually make less news and attention than "death spike" patterns even if their long-term-average numbers are better. If you don't address political patterns, then you will be bulldozed by trolls and demagogues who leverage emotion and vague impressions. If you go on the news with death-rate charts, you'll be ridiculed by the same people who beat up and shunned nerds in school. I'm just the messenger.

Re: Fact-check: Five claims about thorium made by Andrew Yang

#94

Post by acidburnNSA »

pfdietz wrote: post #91
acidburnNSA wrote: post #15

Earlier quoted context omitted.

A few points: * Uranium-Plutonium fuel in a closed cycle can burn all the transuranics and have very low radiotoxicity waste as well. * Molten salt fuels are 10x less dense than typical solid fuels, implying an increase in waste volume. They're also water soluble and frequently liquid. This complicates waste disposal and transport. Not terribly, but still. A good summary reference on radiotoxicity vs. reprocessing is…

A uranium-plutonium fuel in a closed cycle can do that if you have fast reactors. Thermal reactors, no. And the higher transuranics become increasingly difficult to burn, since the delayed neutron fraction goes way down. A reactor burning higher transuranics will be right on the knife edge of prompt supercriticality.

> A reactor burning higher transuranics will be right on the knife edge of prompt supercriticality.

Meh, that might be a bit of an overstatement. Yes, plutonium-driven fast reactors have a delayed neutron fraction around 0.0035 down from 0.0065 in a U-235-fueled fast reactor. The relatively large delayed neutron fraction from fast fissions of U-238 helps out along the way. You can reduce the radiotoxicity of TRU even if you continue to load some U-238. The inert matrix fuels with no U-238 at all get more interesting from this perspective (also from the Doppler effect), but most people don't envision using these.

In fluid systems, more than half of the fuel inventory is off in a heat exchanger out of the core, which means the delayed neutron fraction is cut roughly in half in those systems too (the delayed neutron precursor decays happen where neutron importance is near zero).

Plutonium-fueled fast reactors can be operated with good margins of stability.

Re: Fact-check: Five claims about thorium made by Andrew Yang

#95

Post by pfdietz »

acidburnNSA wrote: post #94
pfdietz wrote: post #91

Earlier quoted context omitted.

A uranium-plutonium fuel in a closed cycle can do that if you have fast reactors. Thermal reactors, no. And the higher transuranics become increasingly difficult to burn, since the delayed neutron fraction goes way down. A reactor burning higher transuranics will be right on the knife edge of prompt supercriticality.

> A reactor burning higher transuranics will be right on the knife edge of prompt supercriticality. Meh, that might be a bit of an overstatement. Yes, plutonium-driven fast reactors have a delayed neutron fraction around 0.0035 down from 0.0065 in a U-235-fueled fast reactor. The relatively large delayed neutron fraction from fast fissions of U-238 helps out along the way. You can reduce the radiotoxicity of TRU even…

I was talking about elements beyond plutonium.

Re: Fact-check: Five claims about thorium made by Andrew Yang

#96

Post by Grue3 »

IshKebab wrote: post #88
Grue3 wrote: post #77

Yeah, let's bring down one of the few candidates who is actually treating climate change seriously with a bunch of nitpicks. Nevermind Bernie Sanders and Elizabeth Warren wanting to shut down the entire nuclear power fleet.

I don't get the nuclear fetish. Wind and solar are already far cheaper. I'm sure you're immediately thinking "but they don't work all the time!". That's true but we're still pretty far from having enough wind/solar to turn all other power plants off even when it is windy and sunny. Also the cost estimates of nuclear don't include decomissioning because nobody has actually decomissioned a nuclear power station yet so…

Wind and solar are not at the scale we need to replace all the coal and gas plants. Nobody has build enough wind and solar at this scale so we don't know how much it costs to permanently maintain that setup (a lifespan of a solar panel/wind turbine is pitiful compared to nuclear).

Decommissioning costs can be considered once the planet is carbon neutral, which it is not right now. Right now the goal is to build up carbon-free energy generation. That said, if you ask the right people [1] they probably can give you an estimate.

[1] http://www.japc.co.jp/english/project/haishi/decommissioning...

Re: Fact-check: Five claims about thorium made by Andrew Yang

#97

Post by thebean11 »

solveit wrote: post #51
thebean11 wrote: post #45

Earlier quoted context omitted.

Nuclear accidents have unique and sometimes unpredictable environment impact, like Fukushima continuing to pollute the ocean with radioactive material to this day. Not saying that's a good reason to swear ourselves off nuclear, but it's more complicated than low carbon emissions.

Everything has unpredictable environment impact at this scale. Name one energy source that can replace nuclear that doesn't have hard-to-predict consequences of unknown but possibly gigantic magnitude on a global scale.

That's exactly my point, nuclear is not some magical exception to this rule
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