The Big Let Down in Molten Salt Nuclear Fission

Huh.

I thought the science was settled.

So did I. At least this is the way everything was presented in the media blurbs, online, and in print. WTF, over? Apparently, the two graduate students forgot to do due diligence peer review before shooting off their mouths.

Either that, or someone does not want these reactors to be deployed, in a major way.

Can you (or I) spell: "vestedinterest"?

Thorium more plentiful than uranium, twice as efficient.....What's the downside again?

It was going to be (supposedly) the one reactor to gobble up "spent" fuel waste. Well, apparently it can't do that. It was going to produce 75 times the fuel efficiency of light water, but it can only to 2 times the fuel burn.

I thought the Thorium design was to enable rare earth mining in the US.....

" Thorium has nearly 200 times the energy content of uranium "....

Is this statement correct or not?

"Three to four times more plentiful than uranium, today's most common nuclear fuel, thorium packs a serious energetic punch: A single ton of it can generate as much energy as 200 tons of uranium, according to Nobel Prize-winning physicist Carlo Rubbia. "

http://www.popularmechanics.com/science/energy/a6162/the-truth-about-thorium-and-nuclear-power/

Plentiful.... check

energy density....check

safe....check

Enable rare earth mining.....check

I think somebody has an agenda here, that does not serve our best interest....

I do believe the deal is still in the works for Thorium. Thorium is the fission fuel of the future!

There are always ulterior motives at play in these large research universities. I would not trust them any further than hurl distance. I think Energy Sec. Perry needs eyes on this situation.

Well it seems to me this waste of rare earth materials is unbelievable, we could be the world's largest supplier with all these high paying jobs created in America...This alone would be reason enough to start using thorium as a clean fuel....a clean fuel that can be used to create not only electricity but valuable process chemicals as well....One mine in Florida could create billions of dollars in profit with very little investment....One way to bring jobs back from China is to make this happen....

I can't find any basis for that statement. Only the quote seems available. Maybe he was discussing ore?

Thorium still requires conversion into uranium for use in a fission reactions for power, so without specifying the isotopes the statement cannot be universally true. Additionally the energy from fission of a mole of u233 from thorium will not be even an order of magnitude greater (much less 200 times) than the energy from fission of a mole of u235.

Noble laureate or not, extraordinary claims require extraordinary support.. truly, some support would be better than none.

While I agree that the initial claims by MIT grad students (which were definitely not LIFTR designs) needed a lot more research of the physics put into the source material and peer review, the entire concept of the future of fission energy utilizing thorium is a separate picture.

I think you fail to realize that LIFTR has the capability to not only consume the thorium introduced, but can be used in breeder mode to produce even more fissile material.

I think the only requirement to start LIFTR is the injection of thermal neutrons from a hot source. This can happen perhaps by seeding the molten salt with some U233, or even other material.

One of the greatest challenges with LIFTR design is the containment material (one of the Hasteloy metals, a relatively new one) that resists the corrosive aspects of fluoride salts. People overlook the advantage of MSR designs, however, in that the molten salt itself is not required to be under pressure in the primary core and heat transfer areas. Some SBR designs will operate at lower steam temperature also.

I've got a decent handle on how a thorium reactor would work. For example, I can tell you that if you think 'consuming the thorium introduced' and being used in 'breeder mode' are somehow different processes, you don't have a good grasp of what's going on.

Thorium is bred to uranium which undergoes fission. It is all 'bred' in that sense. That is why a thorium reactor must be started with something like uranium235.

I still don't understand how they are arriving at thorium having 200 times the energy though.

Surely they meant the resource is much larger in terms of relative elemental abundance of Thorium vis a vis Uranium in the Earth's crust.

That seems much more reasonable.

Thorium still requires conversion into uranium for use in a fission reactions for power

Yep! Just have Pl170 emit alpha then Be6 which will emit Neutrons then bombard the Th for 21 days and it will start to breed itself.

However it will not convert 100% and around .1% will be U232 which emits gamma.

(i think i got the numbers right?)

I worked at DOE, Division of Naval Reactors, when the thorium fueled light water breeder reactor was running.

The conclusion of the project was that it would take heavy water to get it up to a reasonable fuel breeding rate and ended up cancelled.

The fuel initially loaded was Th232 plus enough U235 to go critical and run through a cycle of operation. The fuel breeding cycle started with Th232 plus neutron goes to Th233 and starts a five or 6 stage decay cycle that ends up at U233, which is the end fuel. It's a simple chemical extraction. However, the decay stages before arriving at U233 were intensely radioactive and made handling the spent fuel nearly impossible without substantial, dedicated handling facilities with lots and lots of shielding.

The intense radioactivity during the fuel simmering cycle made the processing of thorium impractical for fission bomb production. The U233 also generates too many spontaneous neutron emissions to make even implosion work. A freshly irradiated thorium fuel load would, however, make a nasty dirty bomb as it would become more radioactive over time rather than following a typical decay curve. As a result, I'm less in favor of thorium fueled reactors unless they are suitably protected from misuse.

Very interesting! I wonder if the same parameters prevail when the medium is molten salt Lithium Fluoride Thorium? AFAICT - there is really no requirement for the fuel to be in solid form: Intervening MSHX would lessen the radiation incident at the LWHX.

But you are stating very clearly that the thorium products get hotter over time, totally contradictory to what the MIT kiddos were saying early on in this exercise.

That certainly makes the thing appear less desirable to even experiment with.

I hope the Chinese don't find out a breakthrough secret of making this work very safely, and end up leaving us in the dust in nuclear power generation. It is after all estimated the Chinese could operate for 20,000 years on Thorium resources they own.

As long as you start the Th232 to Th233 capture, then you are locked into the decay product path.

At one time it was thought that uranium was a rare element available from Joachimstal, the Congo and Canada and General Groves tried to corner the market by buying it all. Turned out it's everywhere, just about. For thorium, one of the more prolific sources is Australian beach sand.

I thought all along it was Titanium sourced from Aussie beach sand. If Thorium is there too, I guess their Coleman lamps do OK there.

Two local foundries got into issues with the local anti-nukes during the '80s for using Australian thoria beach sand in their molding sand mixes. The anti-nuke groups got the Portland city council to pass an ordinance that you could not discharge radioactive materials above a certain level. The level was low enough that thoria sand and olivine sand could not be discharged. The level was also low enough that a normal person could not be buried in city limits, so an exception was included in the law for disposing of dead persons.

At Trojan Nuclear Plant we always used Coleman lantern mantles to spot check function on radiation survey meters to confirm meter operation. The mantles were radioactive from the thoria, but it was that good, natural, organic radioactivity and not that nasty old anthropogenic radioactivity.

'...What's the downside again?...'

There are several significant obstacles/downsides.

Two that stand out are:

1. Reactor power stability/control which, despite the hype, puts safety into question; and

2. Hot, in situ, fuel reprocessing, at power.

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Consider control and stability of reactor power first.

Most neutrons in reactors are prompt neutrons. That is, they come directly from a fission event, fairly immediately, i.e. the vast majority of neutron population comes from the fission events directly and occur within roughly 10 nanoseconds. This means that considering just prompt neutrons the effective generation time is on the order of 10 nanoseconds, or 100 million generations per second.

That is a very small amount of time for making changes.

This is a super simplified example..... Assume you had a reactor with only prompt neutrons operating at 80% power and an addition of reactivity caused the neutron population to grow by 1/10th of 1% each generation. Let's assume the dominant sources of negative feedback can respond very quickly and instantly remove excess reactivity after 1 millisecond. What power level will be reached by the time the magic control system kicks in to stop the increase in power 1 millisecond later?

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80% × 1.001^100000. = 2 ×10⁴⁵ % power.

^boom

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Luckily there are delayed neutrons that make things controllable in a more reasonable time frame. Delayed neutrons come in large part from fission fragments/decay daughters and can arrive a couple seconds up to several minutes later. Great. There is our handle to steer the reaction.

Delayed neutrons make up less than 1% of the neutron population at power, so not a very large handle, but it can work well with good engineering.

It isn't difficult to understand why a proposal to cut the size of that small handle in half should draw attention and require close examination. This is one of the weaknesses of Thorium reactors. U-233 (thorium) has a delayed neutron fraction from fission that is less than 40% the delayed neutron fraction of U-235.

Now, I know thorium molten salt reactors repeat the can't melt down mantra, but they may be playing with words here...as a a molten salt reactor is already molten. Can there be a criticality accident? If they say 'no', it's time to take their lab keys.

That isn't a stand alone reactivity/criticality problem. Circulating the fuel in hopes of removing fission product poisons also means delayed neutrons may not occur in time to be in the area where criticality is desired to be maintained....and if you leave those delayed neutron precursor fragments in close proximity long enough, they could certainly act as poisons.

Thorium also is not as sensitive to doppler resonance negative reactivity feedback. There are significant concerns about positive reactivity feedback with the molten salt reactors.

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The second big problem mentioned above is the idea of reprocessing fuel at power from the primary. This seems highly problematic with the radiation levels likely, the guaranteed equipment breakdown and the exclusion of people until shut down for significant periods.

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There is also the problem of significant tritium production and leakage.

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Thorium sounds dreamy. I expect it to continue to sound that way until a lot more work has been done.

It's too bad that the initial estimates were so overblown. The actual results will be compared with the initial estimates rather that with competing technologies.

Really? that's all you get out of this? I think it's rather obvious this statement was taken out of context...

http://thoriumenergyalliance.com/ThoriumSite/resources.html

http://www.transatomicpower.com/wp-content/uploads/2015/04/Neutronics-White-Paper-v1.1.pdf

I do not believe the gray beards know it all, but they have a hell of a lot more physics experience than these youngsters.

The only real way to know how well or not well the new MSR design will ultimately perform is to build it, and see what the hell it does.

Well China has already started...

http://www.nextbigfuture.com/2016/10/update-on-liquid-fluoride-thorium.html

Or maybe they're not overblown, it could be vested interests, as JS has suggested. (I'm definitely not qualified to say one way or the other.)

I'm thinking this factor of energy efficiency has to do with how efficient the "Breeding" is and there is probably a lot of uncertainty there. So if we build it, we'll find out if it's 75X or 2X. Either way, it's a win.

The big plus with Thorium is you can't make bombs out of it, so the development of reactors can proceed a lot more freely without the worry of material getting into the wrong hands. Just this factor should be enough to warrant pursuing it.

In Thermodynamics, we do not have the knowledge of that 75 times the fuel efficiency.

Given say at best or the carnot efficiency of a thermal engine 28% x 75= 21 times the fuel energy content. Wooohh It only happens inside a blackhole that is.

As usual no idea what you are blathering about. The efficiency referred to is fuel consumption efficiency, not the thermodynamic efficiency of the motive fluid cycle.

Try reading and paying attention, please.

Yes the burn up of the fuel is what reduces the waste, and the radioactivity and half-life of the waste is what makes containment, handling and storage expensive...Reducing these factors and the inherent safety of the design, along with availability and the need to eliminate this blockade to rare earth mining, are all positive factors....Not to mention the jobs and industry it would create...

I'm not saying that more research is not necessary, what I am saying is that we should be working on it.....while the thorium salt reactor design as it is may not be desirable at this time, the possibilities and promise are worth exploring...

https://en.wikipedia.org/wiki/Thorium

https://en.wikipedia.org/wiki/Decay_chain

https://en.wikipedia.org/wiki/Generation_IV_reactor

Question, is the fuel no heat content/energy? Then its all the same that is.

Open brain cavity - insert re-hydrated brain. Then re-state your blathering.

If there is no energy content, then why call it fuel? Why not call it a rock, stupid, or a stupid rock.

You are definitively the most absurd, and sick person who has ever appeared on this forum. Just because Engrish is not her 1st Language is no reason to ridicule.

You should see how poorly I get along in Mandarin, Japanese, Korean, or even Russian!

Heck I can barely manage Spanglish, having grown up in it. German is twice as hard now, although I had it down pat in college.

By the time you age, you will wish you had respected your elders. Go read the Bible, and get some free wisdom.

Hear, hear!

Here, here, and there there! Someone is not all there. Hear ye, Hear ye, in days of old was once "Hoy ye, Hoy ye!" (depends on Cockney accent?)

It would be interesting to know exactly what they found wrong.

However, there are other versions of the fast reactor; we must go back to one of them. I tend to favor the Integral Fast Reactor (IFR) maybe because it is the first one I read much about in recent years. It is cooled by liquid sodium. Another version is cooled by liquid lead, and there are others. They will all get roughly 100 times more energy from the fuel because of better utilization of the uranium in it. Plus waste that is less radioactive and that has a drastically shorter half-life.

One book to read is Plentiful Energy-the Story of the Integral Fast Reactor written by Till and Chang who were supervisors during the experimental development at Argonne National Laboratory. This development, almost ready to move past the experimental stage, was stopped by President Clinton in 1994.

That sounds a lot like what the MIT students were talking about, except theirs was based on molten salt, and used a freeze plug to hold the molten salt in primary loop, that would melt upon loss of power (catastrophic external event), that would drop all the fissile material out of primary to containment (bermed up concrete or something like it, that would spread out the neutron flux, and stop fission cold in its tracks. Within 2-3 days (as the blurb stated), the molten mass would be cold as a stone both in terms of heat, and in terms of rads.

I am not knocking the metal cooled reactors, each has their + and - list.

As to total energy yield by increasing (by a large number) the fuel burn efficiency from a few per cent up to 70-90%, yes that would be a tremendous revolution in fission energy production, since most of the problem now is what to do with high level and low level wastes that are quite voluminous.

Naturally P. Clinton would have stopped anything that looked like, smelled like, tasted like, felt like, or sounded like progress. What a sorry bastard he was and still is.

Big picture view:

1. The technology appears to be workable and comparable to or better than current technology.

2. On line fuel reprocessing is not an option. The irradiated thorium has to age for a period of days to weeks before it decays to U233 which can then be chemically separated and reintroduced to the fuel stream. Concentration of U233 will be in the low hundreds parts per million.

3. Fission products must be chemically removed from the bulk of the fuel. There may be commercial uses for such products, the most common fission products being radioactive iodine used for medical thyroid treatment, strontinum 90 for thermal batteries and xenon for leak detection. The remainder of the chemicals and waste products need to be dealt with.

4. U233 is a poor candidate for any sort of weapon except a fizzle due to high spontaneous neutron ejection. Irradiated thorium would make a nasty dirty bomb. Theft of irradiated thorium is likely to kill the handler...self correcting problem.

Cool. At least might be one problem solved (automatically).