ThorCon nuclear reactor/Debate Guide

Nuclear power is a controversial topic, and some of the controversies remain unsettled, even after the facts in the article are agreed on. This Discussion page will provide a concise summary from each side of these unsettled issues. Much of this discussion is collected from internet forums, and we welcome updates to improve these summaries.

Risk of proliferation

Union of Concerned Scientists report: "Advanced" Isn't Always Better, Edwin Lyman (2021).
https://www.ucsusa.org/resources/advanced-isnt-always-better
“We studied the most prominent 'advanced' nuclear reactor designs. Unfortunately, few are safer or more secure than current generation reactors.”
From the Executive Summary:
“All MSRs chemically treat the fuel to varying extents while the reactor operates to remove radioactive isotopes that affect reactor performance. Therefore, unlike other reactors, MSRs generally require on-site chemical plants to process their fuel. MSRs also need elaborate systems to capture and treat large volumes of highly radioactive gaseous byproducts.”

From Jack Devanney, Principal Engineer, ThorCon USA Inc:
“For the record, ThorCon does no chemical processing online to remove fission products or anything else. Xenon and krypton bubble out in the header tank, are held in storage tanks until they have decayed to harmless levels, and then cooled, compressed and stored. There's nothing elaborate or complex about the process.”

Waste Management

For more discussion see the Discussion page of Nuclear waste management

Increased waste from Small Modular Reactors

National Academy of Sciences report:
Nuclear waste from small modular reactors, L.M.Krall, et.al., PNAS, 31 May 2022, https://doi.org/10.1073/pnas.2111833119
From the abstract:
"the intrinsically higher neutron leakage associated with SMRs suggests that most designs are inferior to LWRs with respect to the generation, management, and final disposal of key radionuclides in nuclear waste."
"water-, molten salt-, and sodium-cooled SMR designs will increase the volume of nuclear waste in need of management and disposal by factors of 2 to 30."

From Jack Devanney, Principal Engineer, ThorCon USA Inc:
"All fission reactors produce essentially the same amount of fission products per thermal energy produced. This is immutable physics. Designs with higher thermal efficiency produce less fission products per kWh electricity produced, but this difference is less than a factor of two from the clunkiest LWR to the fanciest paper HTGR. Either way the amount of spent nuclear fuel represents a beautifully small problem."

For a critique of the NAS report see:
https://neutronbytes.com/2022/05/31/stanfords-questionable-study-on-spent-nuclear-fuel-for-smrs

Radioactive gases

Comment in a discussion of the ThorCon design at SkepticalScience.com:
"ThorCons Cs-137 claims also do not stand up to scrutiny. Much Cs-137 is carried out of the salt in the noble gas stream. They have to say what they plan to do with the Cs-137 that is mixed with their radioactive noble gasses. If it remains in the salt they have to explain how that occurs."
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Comment in a discussion of nuclear waste in the FaceBook group Renewable vs. Nuclear Debate
"What are they going to do with the radioactive gases and the corrosive, radioactive salt from thorium reactors? ...the engineers designing MSR's don't know yet exactly, what kind and what amounts of radioactive waste will be produced, while physicists like Harald Lesch for example warn about the storage of used, radioactive salts. And recycling of nuclear waste is a no-go in the US of A"

Replies: from Jack Devanney under Risk of Proliferation, and from Roger Blomquist in the discussion linked above.

What about non-fuel waste

Question in the FaceBook group Renewable vs Nuclear
"all the stuff on the primary loop. Pipes, pumps, wiring, blah blah. Obviously there is going to be mechanical and chemical wear on parts and they will need to be replaced like any power plant relying on heat -> steam -> turbine -> generator process. Parts will be be additionally exposed to neutrons and presumably undergo nuclear reactions and I assume some of those reactions will compromise their mechanical properties... eventually. How big of a deal is this? Is it slow, fast? What is the balance of fuel waste to non-fuel waste? Where do these parts go?"

Answer from World Nuclear Association Recycling and reuse of materials from decommissioning

Recycling materials from decommissioned nuclear facilities is constrained by the level of radioactivity in them. This is also true for materials from elsewhere, such as gas plants, but the levels specified can be very different. For example, scrap steel from gas plants may be recycled if it has less than 500,000 Bq/kg radioactivity. This level however is one thousand times higher than the clearance level for recycled material from the nuclear industry, where generally anything above 500 Bq/kg may not be cleared from regulatory control for recycling.

Answer from Captain Roger Blomquist, United States Navy (retired) 8 Feb 2022:
"There are small concentrations of activated structural elements like cobalt. These typically have half-lives of years, not multiple decades. If they are recycled, then the workers doing the recycling will need to take (sometimes expensive) precautions to minimize their radiation exposure. I doubt that any such exposures would be harmful, although some might be. The precautions are quite likely far in excess of what is needed to prevent actual health effects."

Question on Quora.com

How big a problem is irradiated steel and other non-fuel waste from a nuclear power plant?

Add image caption here.

Answer from World Nuclear Association discussion of Recycling and reuse of materials from decommissioning:
Decommissioned steam generators from Bruce Power in Canada
"These steam generators were each 12m long and 2.5m diameter, with mass 100 tonnes, and contained some 4g of radionuclides with about 340 GBq of activity. Exposure was 0.08 mSv/hr at one metre." This compares to a chest x-ray (0.020 mSv) or the minimum exposure to show a measurable increase in cancer risk (100 mSv) XKCD Radiation Chart

Answer from Lyle McElhaney 30 March 2022:
Iron is an element that is difficult to make radioactive.

This table shows that iron-56, which is almost 92% of all naturally occurring iron, requires three neutron absorptions before it becomes radioactive, and two absorptions for another 2% of the material. A single absorption is a low probability event for any given iron nucleus; absorbing three is a low probability to the third power. If it does happen, it results in iron-59 which beta decays to cobalt-59 (stable) with a half-life of 45 days.

Of course, it also shows that about 6% of iron will become unstable with the absorption of a single neutron. The resulting isotope decays by electron capture, which does not emit a particle other than a neutrino, and results in manganese-55, which is stable. So, no harm done by that other than possibly some gamma-rays.

The cobalt-59 resulting from a triple neutron capture could catch another neutron, becoming the dreaded cobalt-60, nemesis of the cobalt bomb. Cobalt-60 has a powerful gamma-ray emission as it beta decays with a half-life of around 5 years. This requires, as noted, 4 successive neutron captures with an intervening beta decay after the third. It is a very small probability event in concept; I don’t know what it is in practice.

Other materials - some do become radioactive when drenched with neutrons for an extended time. One would need to know what materials to analyze what happens.

Question in the FaceBook group Americans for Nuclear Energy
I've heard that the steel gets brittle. Is that just the surface? Can it be annealed with a torch and returned to service, or do we have to discard 343 tons of radioactive steel every 8 years?

Answer from Ed Pheil, Chief Technology Officer, Elysium Industries
There are multiple types of steel damage. The type limiting Thorcon to 8 years is fluoride salt corrosion. Less limiting are neutron displacement damage. This is bulk steel damage, not surface. It can be partially annealed by heating the stainless steel to 650C for hours. Another damage is an (n, alpha) reaction in the nickel creating bulk nickel. Annealing makes the helium migrate to grain boundaries, making it more brittle. Also not limiting.
Further there is creep damage, due to high temperature, not neutrons, also not limiting.
The question is the rate of accumulation of each type of damage. Fluoride salt is more corrosive in a radiation field due to radiation creating free Fluorine ions (F-). They chose to use type 316 stainless steel because it is qualified & cheap, unlike Hastalloy-N. Enough cheaper to warrant 8 yr replacement, but also they would have a qualified material to be able to build "today".

Cost

Limited material resources

Comment in a discussion of the ThorCon design at SkepticalScience.com
"ThorCon has 12 mol% Beryllium in its salt mix. There is only one large Beryllium mine in the entire world. From ThorCons' numbers I calculate that a single 1,000 MW plant would use approximately 2.5 tons of Beryllium to start up. Since total world production of beryllium is about 260 tons/year and ThorCons have to be replaced every 4 years, 400 1,000 MW ThorCons (approximately current world nuclear reactors) would use up the entire world supply."
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Editorial discussion

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