Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: matthewh on 23/05/2019 13:36:50
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Vivian sent us this powerful question:
Instead of nuclear scientists chasing their tails on nuclear fusion which will cost probably hundreds of billions of dollars to develop, why don't they turn to Thorium which is far cheaper more plentiful and does not produce radioactive waste that has to be buried? Or is this another ploy by the producers of Uranium to play down the advantages the Thorium route?
Does anyone have an answer?
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Thorium doesn't create a nuclear chain reaction like Plutonium. Plutonium is the only element that does.
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Thorium doesn't create a nuclear chain reaction like Plutonium. Plutonium is the only element that does.
That isn't true. Uranium-235 can create a chain reaction as well.
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While Thorium 232 can be used in a fuel cycle, it is by bombarding it with neutrons in order to create a fissile fuel. It is a breeder reactor type of system. The claim that this would not produce waste is false, as many of the daughter isotopes of this process are dangerous and strong gamma emitters. While there might be ways around this, it requires more advanced technology than a Uranium based reactor.
It needs further research to produce practical results.
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turn to Thorium
There are some advantages in Thorium fission - unlike Uranium and Plutonium, Thorium can't be made into a nuclear bomb.
This means that a country with a large stock of refined Thorium is not a nuclear threat in the same way that a country with a large stock of refined Uranium (for example, see the current spat between Iran and the US, both of which are guilty of holding stocks of refined Uranium).
Some organisations are investigating Thorium - but not so much from the traditional nuclear weapons states, who have a vested interest in continuing work on Uranium/Plutonium (while discouraging anyone else from doing so).
See: https://en.wikipedia.org/wiki/Thorium-based_nuclear_power
...nuclear fusion which will cost probably hundreds of billions of dollars to develop, why don't they turn to Thorium which is far cheaper more plentiful
It seems that you are comparing the abundance of Deuterium with the abundance of Thorium...
- Deuterium was formed in the Big Bang; Thorium relies on collision of neutron stars. I know which one is more common in the universe.
- Hydrogen fusion is far more efficient than fission, in terms of energy out for mass of fuel in
- Hydrogen fusion produces far less mass of radioactive waste, with much shorter lifetimes than fission
- Hydrogen fusion doesn't hold enough fuel in the reactor to melt down the reactor. Fission reactors might (if the multiple-redundant cooling systems fail)
- Hydrogen fusion would be a much better choice for spaceship propulsion, if it can be made small & light enough (long-term goal)
...There are huge advantages for fusion, if/when we can ever get it to work. That's why investing billions now (a small cost on a per-capita basis) has a potential payoff many times larger.
See some of the reasons here: https://omegataupodcast.net/312-the-wendelstein-7-x-fusion-experiment/
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- Deuterium was formed in the Big Bang;
While some deuterium was formed in the early stages of the universe, the vast majority of it is manufactured in stars via the proton-proton reaction in which a pair of protons combine into deuterium, releasing a neutrino and positron in the process.
This is why the isotope is so common in comparison to something like Thorium.
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the vast majority of (deuterium) is manufactured in stars via the proton-proton reaction in which a pair of protons combine into deuterium...
I agree that this is one place where Deuterium is being actively produced today. But it doesn't lead to an increase in deuterium on the Earth (or in the universe).
This is because deuterium fuses into helium very rapidly (even in small, cool, "brown dwarf" stars) - it is the deuterium forming step that limits the rate of stellar fusion in stars up to the size of the Sun (in larger stars, the CNO cycle dominates).
A star, during its lifetime progressively reduces the amount of deuterium in the universe. (This is the same goal as fusion researchers...)
However, in its final moments, a large star going supernova could seed nearby space with some Deuterium through the p-p reaction (provided it hasn't already burnt all its Hydrogen to Helium)..
See: https://en.wikipedia.org/wiki/Stellar_nucleosynthesis#Hydrogen_fusion
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Why don't we use Thorium in Nuclear Fusion?
Because Thorium undergoes fission, not fusion.
See: https://en.wikipedia.org/wiki/Nuclear_fission
https://en.wikipedia.org/wiki/Nuclear_fusion