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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There are several blogs out there that “prove” that LFTR won’t work. If you look closely at what they are saying, they apply facts about solid fueled reactors, including light-water reactors and pressurized-water reactors (LWR/PWR), to prove their point.

But there is almost nothing applicable from LWR/PWR technology to LFTRs, beyond they both have uranium fission. Solid fuel vs. fluid fuel. High pressure water cooling vs. atmospheric pressure stable salts. No removal of fission byproducts (trapped in the fuel rods) vs. removing fission byproducts from liqiud salts. Complex engineered safety vs. inherent and passive safety.

If you’re going to analyze a technology, you can’t simply take someone’s sloppily written ideas about a very different technology; they won’t apply. You take your knowledge and experience from other technology’s problems and solutions, and find out how well they apply. is referred to by several people. But it’s full of misunderstandings, sloppy writing so you’re not clear which type of reactor he’s talking about, and little analysis of LFTRs actual design and workings.

Much of what he says “against LFTR” doesn’t apply to LFTRs, but rather to PWR and LWR.

“This would be very technically challenging, especially in the LFTR case given the importance about separating out of U-232 (and its Thallium-208 payload) from U-233 or indeed removal of protactinium-233 as well as a host of other nuclear ‘poisons’ discussed. Build up of these in the core both leads to increased irradiation of the core as well as the eventual shutdown of the nuclear reaction process altogether.”

Many inaccuracies in one paragraph.

You wouldn’t remove protactinium-233 from a LFTR — when thorium absorbs a neutron, it decays to protactinium-233, then to uranium-233. He’s talking about removing the fuel! In a LFTR, you circulate the blanket salt (that has thorium, some decaying to protactinium then to uranium) through a simple chemical processing section, to extract the uranium from the blanket salt and deposit it into the core salt.

You would not remove U-232 from a LFTR. It is a gamma ray source, providing anti-proliferation benefits; in the reactor it will absorb a neutron and become U-233; then it fissions. He’s confusing solid-fueled (probably LWR and PWR) technology with liquid-fueled technology.

“increased irradiation of the core”

What does that mean? A nuclear reactor is designed to create radiation in the core (and keep it there). Does he mean to say that in a solid-fueled reactor, fuel rods get damaged by radiation?

“eventual shutdown of the nuclear reaction process altogether”

Sounds like he’s again confusing solid-fueled (LWR and PWR) technology with liquid-fueled technology. In a molten-salt reactor, fission byproducts are easily removed from the circulating salts. A fast-spectrum molten salt reactor would not require batch processing of the salts for decades.

See Fast Spectrum Molten Salt Reactor Options, Oak Ridge National Laboratory 2011

See D. LeBlanc / Nuclear Engineering and Design 240 (2010) 1644-1656 (most of the papers published in this publication would be about PWR and LWR, but this paper is on molten salt reactors).

“the real radiological hazard is a pipe burst (an all too common occurrence and any chemical plant, and especially likely at these sort of working temperatures and radiation levels), we would thus need to put the CPP [chemical processing plant] underneath our concrete containment dome.”

Well, he’s clearly talking about LWR/PWR, since LFTRs don’t need concrete containment domes (there’s no high pressure water to contain). Pipes definitely could leak in a LFTR, but they wouldn’t “burst” at atmospheric pressures.

“yet to come up with a functional design of an CPP… materials science and chemical processing technology has moved on hugely in the last 40 years, so I doubt it would be sensible to build an CPP as shown in these plans. A new one would have to be redesigned from scratch.”

Yes, new would be better. But couldn’t it be that the 1960s design worked? Could it be that removing xenon gas is as easy as spraying the molten salt in a chamber, so the gas could come out of the liquid and be collected? (ORNL demonstrated it working in the MSRE.) There are other examples of the different chemical processing needed, all much simpler than he’s talking about, in ORNL documents from the 1960s and 1970s, and newer publications from several sources. I haven’t seen engineering specs, but the technology for the required chemical processing is known (and much of it used in the MSRE).

A “functional design” of a CPP would be designed to match the size and type of reactor being built, and we will see only simplified versions, just like in any industry making a new product. However, there are scientific journals going over designs, for example the links I’ve included.

“The designers of this reactor seem to be assuming that this CPP, which will involve various stages of pumping, sparging, vacuum processing and filtering of the working fluid, often at a variety of set temperatures or pressures will operate with no net energy input and achieve 100% separation efficiency!”

Of course it will take energy to pump, filter, electrolyze, etc. Engineers do include these in system designs. You wouldn’t need 100% separation efficiency, you need good enough so the reactor works for the expected lifetime. The designers know that can be done, at better than required efficiency, and when giving overviews of the technology (to people who likely wouldn’t understand detailed engineering and chemical specifications) they say the essential points — we need these capabilities, which are known and understood and have been demonstrated in other industrial applications; and we need these capabilities which are new and need explaining in more detail.

LFTRs are Much more forgiving of fission byproducts than solid fueled reactors — fission byproducts are trapped in solid fuel pellets, but can be removed from the circulating salts in a molten salt reactor.

“As the working fluid will be coming off the exhaust from the heat exchange cycle it will be relatively cool (in the MSRE it was at around 570 °C) yet some of these processing stages will require the fluid to be heated back up to 1,600°C.”

Just because the MSRE ran that temperature doesn’t mean MSRs can not run hotter! Most would be run hot enough (over 650° C), to split water and CO2 for making vehicle fuels. The highest temperature LFTRs would need materials able to handle the heat, and there are research results about which materials would work. I’ve seen suggestions of temperatures up to about 1000° C. (The salts are stable liquids to about 1400°C.) I haven’t seen anything mentioned needing 1600° C. Clearly he isn’t specifying what “these processing stages” are, nor is he starting from what would work in a LFTR. No engineer designs systems that cool down and “require the fluid to be heated back up” unless there is no other way; there are good ways with LFTRs.

“LFTR supporters have suggested (see here) using electrolysis to help improve the filtering efficiency of their plant. An excellent idea, it would solve a number of problems, but unfortunately electrolysis systems practically eat electricity! Where’s all that electricity going to come from?”

Hmm, he seems like he’s serious asking that. I’d guess the designers would get electricity from the electric generators connected to the reactor, wouldn’t you? How much electricity does he think electrolysis will “practically eat” compared to the electric generation capacity of the reactor? Maybe he’s taking knowledge from using electrolysis to make hydrogen fuel cells? (Electrolysis to make hydrogen fuel cells is less efficient than running the car on the electricity, or on gasoline instead of burning oil to make the electricity.)

“…achieved in which we compromise the standards of our CPP, accept one that is smaller and less efficient (and thus our reactor burns much more fuel and produces more waste) but is sufficiently efficient to give us a decent fuel burnup rate without being over complex (or large), nor energy hungry… Inevitably from time to time (probably at least once a year or so) we’d likely need to dump the entire core’s contents and replace it with fresh fuel. The ‘dumped’ contents being added to the global nuclear waste stockpile.”

Is he talking about a LFTR? All the physicists analyzing LFTRs (not saying what they know from solid-fuel reactors) say 95% to 99.5%+ fuel burnup, depending on the design of the reactor. We know the burnup that was achieved in the MSRE.

You wouldn’t “dump” the fuel into a stockpile, you’d remove the fission byproducts in the chemical processing plant, and continue using the fuel. Does he actually believe that since we can’t get 100% efficient, the reactor or fuel won’t work for longer than a year? (Is he talking about fuel in a fuel rod? Is the time he mentions the time fuel is usable in solid fueled reactors? Very difficult to remove the fuel from the ceramics in the rod, to do chemical processing on it.)

When people write things about complex technologies like this, make sure they’re clear about the technology, and write so you are clear which technology their facts or problems or solutions are about.

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