MSR Benefits

Molten Salt Reactor Advantages

  • Molten Fuel - Fuel circulates through the reactor, fission products get removed, for over 99% fuel use (vs. LWR ~3%). No long-term radioactive waste.
  • Salt Cooled - Coolant far below boiling point, reactor operates at atmospheric pressure. Fuel dissolved in stable salt (no water), no loss of coolant accident possible. No need for high-pressure safety systems.
  • High Inherent Safety - No water, no high pressure, nothing that could propel radioactive materials into the environment. Thermal expansion/contraction of molten fuel salt strongly regulates fission rate; MSR is a very stable reactor. Simple safety systems work even if no electricity or operators.
  • Easy Construction and Siting - Low pressure operation, so no high-pressure safety systems. No water, so no steam containment building. Reactor factory assembled, with modern quality control, sensors and communication.
  • Lower Cost - Even with exotic materials, construction costs will be dramatically lower than LWR — factory construction, minimal manual on-site preparation. No long-term radioactive waste, so no long-term storage.
  • High Temperature Operation - Heat to generate electricity, desalinate water, produce CO2-neutral vehicle fuel, etc.
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I responded to the Washington Post article, Nuclear power entrepreneurs push thorium as a fuel with this:

For one thing, [Ingersoll] said, it would be too expensive to replace or convert the nuclear power plants already running in this country

Since our reactors were almost all built in the 1970s, we will have to replace our aging nuclear plants, want to or not. But if he is talking about converting to using thorium instead of uranium in existing solid-fueled plants, then he is no doubt correct.

Whether reactor uses uranium, plutonium, or thorium is not a key issue. Solid-fueled or molten-fueled reactors can use either.

Key differences are solid fueled or liquid fueled; and the type of coolant. The article doesn’t carefully distinguish statements about solid-fueled reactors vs. molten-fueled reactors, nor water-cooled vs. salt-cooled reactors. Ingersoll’s statements are consistently correct about solid-fueled, water-cooled reactors. (I disagree with others claiming Ingersoll is disingenuous or status-quo; I guess his statements about one type of reactor were used carelessly, as is common in articles, not knowing the difference between reactors.)

It will cost less to develop and install LFTRs than to rebuild all our existing reactors. Molten salt coolant remains liquid, so the reactor runs at atmospheric pressure; no high pressure containment needed. Construction costs will be dramatically lower, not needing a high-pressure reactor vessel, not needing a steam containment building (huge reinforced concrete), and not needing complex redundant safety equipment to deal with high-pressure water. See LFTRs Do Not Need High Pressure Containment.

Molten salts have much higher safety as coolant than water (which requires very high pressure to keep it liquid, and boils away if the pressure vessel breaks). See No Water Needed for LFTRs, and no Loss of Coolant Accidents

LFTRs can’t have high-pressure explosions (they operate at atmospheric pressure); can’t have loss of coolant accidents (the coolant won’t evaporate, and is chemically bound to uranium and transuranic elements); can’t have hydrogen explosions (nothing in them generates hydrogen). See Passive and Inherent Safety.

[Ingersoll] also pointed out that thorium would still have some radioactive byproducts — just not as much as uranium and not as long-lived — and that there is no ready stockpile of thorium in the United States. It would have to be mined.

Let’s look at what specifically Dan Ingersoll meant? Current reactors need about 250,000kg natural uranium, to make 35,000kg enriched uranium, to make 1GW electricity for a year. 250,000kg waste (almost all uranium, store for millenia).

Adding thorium mixed with uranium in solid-fueled reactors would give a slight improvement in waste.

Substituting thorium (use no mined uranium except to jump-start the reaction) in a solid-fueled reactor would save 215,000kg waste (no “depleted uranium”), would have about 35,000kg waste for 1GW-year electricity. This is probably what Ingersoll was saying.

A molten-salt reactor would need 800kg of uranium or plutonium or thorium, to make 1GW-year electricity. 800kg waste (no uranium or transuranic elements), store 83% for 10 years and 17% for 350 years. We know how to safely store 135kg (300lbs) per gigawatt-year, for 350 years. See No Long-Term Toxic Waste Storage.

There is thorium at every rare-earth mine, abandoned, plus tons of purified thorium buried in the NV desert. Is there another stockpile of fuel a molten salt reactor could use? Absolutely! Nuclear waste is primarily uranium, fuel for a molten salt reactor. (Unfortunately MSRs consume uranium so efficiently we would have to supply the entire world with USA-levels of electricity and vehicle fuel for a century, to have consumed all our uranium waste stockpiles.) See LFTRs Can Consume Nuclear Waste.

We’re spending more on just the Hanford ‘Vitrification Plant’ — $12Billion — ( than we would spend developing LFTRs and building assembly line manufacturing for them.

If we mine our rare earth metals, we would get thorium as a byproduct. (The USA doesn’t have any active mines for our rare earth deposits, because thorium is considered “nuclear waste”, though so slightly radioactive the half life is 14 billion years, and the radiation is stopped by a thin layer of plastic; one industrial use of thorium is in eyeglass lenses. So China supplies our rare earth metals, for headphones, TVs, windmills.)

“A thorium-based fuel cycle has some advantages, but it’s not compelling for infrastructure and investments.”

More accurate statement would be “A thorium-based fuel cycle has some advantages in a solid-fueled reactor compared to using uranium in a solid-fueled reactor, but …”

This statement is not accurate if comparing a molten-fueled reactor to solid-fueled. Solid fueled reactors only fission ~1% of the fuel; fission byproducts are trapped in the fuel rods and stop the reaction. In a molten-fueled reactor, fission byproducts are easily extracted; the 1960s molten salt reactor fissioned over 99% of the fuel. See No Long-Term Toxic Waste Storage and LFTRs Can Consume Nuclear Waste.

Overall, [Ingersoll] says the benefits don’t outweigh the huge costs of switching technologies. “I’m looking for something compelling enough to trash billions of dollars of infrastructure that we have already and I don’t see that.”

Again, Ingersoll was talking about using thorium in a solid-fueled reactor. Much bigger benefits if we use a molten-salt reactor, such as LFTR. We wouldn’t “trash” reactors, we would use them until need repairs more expensive than replacing them. (Happening Soon.)

Economics of LFTRs make very good sense, see Economics of LFTRs. Flibe Energy plans to have a LFTR operational by 2015; assembly line manufacturing LFTRs a few years later.

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