General Question

Pandora's avatar

Can someone explain the pros and cons of Thorium vs. Uranium and if Molten Salt Reactors are safer and cleaner than what we have now?

Asked by Pandora (28351points) September 5th, 2019

I heard about Thorium from one Andrew Yang interview on CNN last night for an alternative cleaner energy source. I didn’t know what it was so I looked it up.

So far the only thing I understand is that you can find more in the earth’s crust than Uranium because only 1 percent of Uranium found is useable vs. thorium is all usable. Also Uranium doesn’t need outside source to make it react and Thorium need outside energy source to make it react. So if I understand this, if there is a failure in a thorium reactor there should be no explosion vs Uranium will explode in a reactor failure. (Not really sure on that.)

So is this something we should be attempting to do to find quick energy sources to replace gas and coal for large cities where solar panels and wind turbines may not be an option ?

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6 Answers

seawulf575's avatar

I haven’t worked with Thorium as a fuel source. I have worked with Uranium as a fuel source. I know that Oak Ridge Nat’l labs did an experiment with a Thorium reactor back in the early 1960’s. It was not really designed for large power output because it was being tested. It worked and ran for several years. However its operation was very spotty by today’s standards. By that I mean it would operated for a month and then be down for a month due to problems in the system, then it might run for 3 months and be down for repairs. I suspect many of those problems could be worked out over time.
To correct one thing in your question, uranium plants don’t explode. A nuclear bomb is a certain design and geometry where a small amount of uranium fissions all at once and the energy released is the explosion. In a uranium core, the geometry…the way the fissile material is assembled…is such that it cannot explode. The problem with uranium, and I suspect with Thorium, is the decay heat. Decay heat is the energy released from radioactive decay. During the fission process, many radioactive elements are formed. Every radioactive element or isotope will “decay” to another form or element, trying to reach a stable state.
During a fission, usually two or more radioactive elements are formed. These elements continue to decay and give up energy, sometimes for a long time. Look at it this way…when you cook on a gas stove and you turn off the gas, the heat pretty much goes away with the flame. When you cook with an electric stove and you cut the power, the burner continues to be hot for a lot longer. And this decay heat still needs to be removed from the core. In all of the nuclear disasters we had in this world, one of the big contributing factors was the loss of cooling. Three Mile Island had problems where they lost water in the core and exposed fuel. With no water to remove the heat, the fuel rods started to melt, exposing the uranium. At Chernobyl, the core was operating in a bad area and the operator initiated an emergency shutdown. Due to the design of this plant, and what they didn’t understand, this action…the emergency shutdown, actually caused the reactor power to shoot up. This rapid power increase caused the cooling water to flash to steam, resulting in what we saw as the explosion. Then the core overheated and melted. The list of errors goes on, but in none of the nuclear accidents did the uranium explode as it does in a bomb.
Thorium Molten Salt Reactor (MSR) at Oak Ridge, from what I understand, used a liquid of lithium fluoride, beryllium fluoride, zirconium fluoride, and uranium oxide as the fuel. At first they used U-235 in the uranium oxide, but later swapped to U-233. This is important because the U-233 is the active fissionable product in a thorium reactor. From what I can gather, the fissions happened in the liquid and this liquid was cycled from the core to an overgrown radiator where it was cooled by air blown across the radiator coils and then back to the core.
I guess the concerns I would have with MSRs would be more of an engineering sort than a fission sort. Fluoride is highly reactive and corrosive. Using it as part of the molten salt would mean you would need specific materials of construction. Any leaks would be highly corrosive too, I would think, and could present a huge health hazard to those in the area. Another issue is the removal of the heat. The Oak Ridge design used a huge radiator with the idea that the heated gases on the outlet side of the radiator could be used to power a gas turbine. However, that plant was small…less than 10 Mw. Today’s nuclear power plants are closer to 1000 Mw. So I suspect something else would have to be done since trying to build a big enough heat sink in the form of a air-cooled radiator would be impractical. Another concern would be with maintenance. I served on a submarine that at one point used liquid sodium as a coolant for the reactor. The heat transfer from the core to the sodium was great, but if you had a small leak in the steam generator, you could get little (or larger) explosions. Also, if you had to do maintenance on any of the reactor system components, you were suddenly exposed to highly reactive sodium. It made maintenance difficult and dangerous. They phased out that design after only a couple years. I suspect many of the same issues would exist with a MSR.
I suspect the MSRs could be a good viable option to pressurized water (PW) reactors, but an awful lot of work and effort would have to be put into designing them before they could be used as a replacement.

kritiper's avatar

A reaction with uranium is easily started and controlled without an external energy source to maintain it whereas getting and maintaining a reaction with thorium is difficult. That’s why an external force is required for a thorium reaction; it takes energy to make energy.

Pandora's avatar

@Mimishu1995 LOL, cool video. It helped me to better understand @seawulf575 explanation.

@seawulf575 and @kritiper Thank you for the detail explanation. I do wonder if we had stayed working with its since the 1960 if maybe we would’ve found a way to make it work better by now.
@seawulf575 Sounds like scary as hell work. We often take energy for granted and forget there are people who deal with all this scary stuff to bring cities energy. The video after Mimishu video above is an interesting video to watch.

seawulf575's avatar

@Pandora I did it for 36 years. Surprisingly, nuclear power is one of the safer industries. They press safety and error free operation like you wouldn’t believe. It gets down to the minutia like if someone scratches themselves, we have to do investigations to find out why it happened and if further action is required to keep others from scratching themselves. If someone starts to operate an incorrect valve or switch, it becomes a huge deal…even if they don’t actually operate it. For instance, if you grab a valve and start to close it, get it closed ¼ turn and realize you have the wrong valve and restore it, they consider that you operated the wrong component. And it often doesn’t depend on the potential consequences. All errors have reports written about them. All consequential errors have reports written that are shared with the rest of the industry so others can learn from your mistakes and you can learn from theirs. And training is a huge key. There are intricate training programs for every job with regular continuing training. The hazards and potential consequences of operating a nuclear reactor are definitely respected.
The focus on safety is astounding.

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