Thorium-fueled Molten Salt Reactors

With all the current fears and concerns over the state of the worlds oils reserves it is obvious that we need to look at the development of alternate sources for power. Several sources have been suggested but are they truly an alternative.
1. Solar Power- A grand idea but with the current solar cell technology We would have to cover hundreds of square acres to supply our nations needs to say nothing of the world.
2. Wind energy- Another good idea but again the shear amount of space required for wind farms makes this one only an addition and not a singular source of power.
3. Coal- Even with supposed "clean-burning" facilities coal is not an acceptable energy alternative. The harvesting methods are dangerous and also enviromentally destructive.
4. Nuclear Power- Until major advances are made the threat of nuclear disaster outweighs the benefits. But what if their was a safer alternative?
This safer Alternative is the Thorium-fueled MSR or Molten Salt Reactor.
To put it in simple numbers
"One pound of thorium produces as much power as 300 pounds of uranium or 3.5 million pounds of coal where a current nuclear reactor provides the energy equivalent of 1200 windmills or 20 square miles of solar panels." (popular science july 2011 pgs 60-61)
If my math is correct (which may be doubtful) One MSR could therefore supply the equivalent power of 3600 windmills, 60 square miles of solar panels or 3 current nuclear reactors.
It seems obvious to me that with their comparitive energy output and safety that Thorium MSRs should be one of the major infrastructure developments for every city.

 

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Welcome to sciforums Kel.


Thorium reactors have many advantages. India has lot of Thorium and little Uranium so will soon have world’s first (1 of five) commercial thorium reactors generating electric power. Here is Wiki link about them: http://en.wikipedia.org/wiki/Thorium_fuel_cycle WhichI condensed to some major points here: http://www.sciforums.com/showpost.php?p=2308299&postcount=7

For more see: http://www.sciforums.com/showpost.php?p=2718805&postcount=19 where your will can read that
1) China is serious about building them too.

2) Why world went down the wrong Uranium path despite building small thorium reactors first at Oak Ridge - easier as essentially no enrichment needed (Only to get tiny fraction of U233 for initial fire up but later none is needed as self produced).

3&4) Some inherent safety features and it superior economics.
Part due to Thorium being a free by product that must best separated from rare earths and in part because 100% of it, not only U’s only 0.7%, is nuclear fuel.

5) Plus link to non-sciforums articles on the Thorium reactor.

 

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A lot more than that; we'd have to cover a square of desert 84 miles on a side with currently available PV to meet all our electrical energy needs. Fortunately we have a lot of empty desert, which is also (coincidentally) where we get most of our sun. If we really went this route we'd have to dedicate 0.2% of the land in the US to power production, which doesn't seem like a lot to me.

However, generating 100% of our power this way would be wasteful since it's hard to store at night.

Also agreed. It could supply a significant fraction but not all.

Thorium reactors cannot generate power without other fissile materials. You need a plutonium or uranium core to provide the neutrons to "breed" thorium into uranium; the reaction then starts. Thorium is thus not itself a power generator, but it can be used as a power amplifier (to increase the power of the uranium core, for example.)

Another alternative is to build a neutron accelerator capable of injecting enough neutrons to transmute the thorium to uranium and start the reaction. No one has ever built a neutron accelerator capable of the power levels required to start the reaction though.

A reactor that relies on molten salt at thousands of degrees C is also not all that safe during an accident. Any water that enters the system results in a very violent explosion and production of hydrofluoric acid, the most corrosive acid we have discovered. Its effect on both people and the reactor itself (it will even dissolve glass) is pretty significant.

If you're looking for cheap reactor fuel, unenriched (i.e. raw) uranium can fuel a CANDU reactor, and we have a lot of experience operating them.

Overall I think thorium reactors have some promise, but a lot more work has to be done before we consider them for any commercial applications.

 

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Wait wait wait a minute, didn't we already have a thread like this one?

 

Yeah, most likely we do, as we are very redundant, very redundant here sometimes...:shrug:

...and Boston Electric has been installing those solar panels on residential rooftops instead of out in the desert already. They state that this program has forestalled the need to build 2 new coal fired generators in the Boston area as a result. So you can keep on poo - pooing solar, wind and bio-fuels as much as you wish, the rest of us are going ahead and making the switch.

As we all know by now, I have been using solar for 32 years now and am tickled frikkin pink at the savings I have accrued as a result.

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That is all basically false. You need to read some more about them.

True the thorium reactor needs a little bit of U233 (or 235, which could be diverted to bomb use) to run and you must give is some when first starting, but it produces more than enough U233 as it runs so no more needs to be added. I.e. after startup the ONLY fuel used is thorium.

I think you are also you error in that you are NOT “breeding thorium into uranium.” I.e. Think the energy comes from splitting thorium but am not sure of the inter reactor nuclear reactions.

In any case: “Thorium is thus not itself a power generator, but it can be used as a power amplifier (to increase the power of the uranium core, for example.” is also an error.

While you can get one started by injected neutrons, building a proton accelerator for making them (you can’t accelerate neutrons) is very expensive compared to cost of a onetime separation of a small amount of U233, which takes LESS “separation work” units than separating U235 from the dominate U238 ore as the mass difference is 5, not only 3. AFAIK, none of the thorium reactors being built will inject neutrons. India should have their first in commercial service in late 2012 / early 2013, with four more a few years later on line too, as I recall.

Thus this “a lot more work has to be done before we consider them for any commercial applications.” also false.

Oak Ridge ran the first thorium reactor back in 1960. The obvious way to get reactor experience before a massive separation plant was built there for A-bomb production. The US only went down the "Uranium Road" as you cannot build a bomb with Thorium. After WWII ended The AEC handed over to the electric power industry their well developed uranium reactor technology – The wrong choice, but that is what happened.

I don’t know the planned operating temperature but some designs are not pure molten thorium fluoride but lower melting point eutectics. For example: “Charles S. “Rusty” Holden, founder of Thorenco LLC, did offer a specific design: a 40MW pilot plant that he called “a little LFTR.” Using fissile uranium-235 as a source of ignition neutrons and a mix of thorium tetrafluoride in a beryllium fluoride molten salt, Thorenco’s design includes a deep salt pool with a honeycomb geometry that offers “a superior way to clean and condition the fuel during operations,” Holden said.” From: http://energyfromthorium.com where both pro & con POVs are presentd.

Note also the use of U235, which there is a huge surplus of as bombs are decommissioned. Thorium is a free by-product of production of rare earths, which being a radioactive problem for them, they may even pay you to take it away. The California mine, MolyCorp is now trying to reopen, was shut down because of improper disposal of thorium. Currently, from it the US has already-mined supply of 3200 metric tonnes of thorium in Nevada that will meet US energy needs for many decades. Thorium is at least three time more abundant than uranium in Earth’s crust and 100% of it is fuel (only one isotope) not just the 0.7% of uranium that is useful as fuel!

As far as safety is concerned:
“…Dr Cywinski, who anchors a UK-wide thorium team, said the residual heat left behind in a crisis would be “orders of magnitude less” than in a uranium reactor. Chinese scientists claim that hazardous waste will be a thousand times less than with uranium. The system is inherently less prone to disaster. “The reactor has an amazing safety feature,” said Kirk Sorensen, a former NASA engineer at Teledyne Brown and a thorium expert….”

“…Note that the utilization of the released neutrons is a function of geometry. A sphere needs fewer to sustain the reaction than a thin slab. A hemisphere, which could be the shape of the molten Thorium core if the spherical tank holding the molten thorium is only half full, it needs slightly larger than a full sphere, but far fewer {neutrons escape than from} a thin slab, from which almost all released neutron would just escape instead of sustain nuclear chain reaction.

Thus the spherical tank holding the reacting liquid thorium has a metal plug in the bottom, which melts, if the thorium core begins to overheat, as it could if the pumps supplying the water to be turned into steam should fail. Then the molten thorium runs out of the bottom of the sphere and falls into a large flat pan, where most neutrons escape to the air - the chain reaction immediately stops.

The entire shut down depends only on gravity, no need for cooling water or electrically driven "control rods" etc. which can warp and jam, etc.I.e. SAFE, fully automatic, shut down only requires gravity.No water, no pumps, no electricity, no control rods plunging into the core, just gravity. Also note there are no fuel rods, clad with zirconium, which can (and does) react with hot steam to produce hydrogen and then hydrogen explosions.

All these “safety points” from: http://www.sciforums.com/showpost.php?p=2718805&postcount=19
Which I hope you will read to become better informed and then point out any faults with information there and in the external links given there (and in post 2).

 

I agree that solar, wind and biofuels are important but we cannot rely on them as a sole source of power. The world population is expanding at a near exponential rate and world power demands will continue to sky-rocket. I applaud your use of solar energy but for some people it is not a feasable alternative. If I could afford I would convert to solar in a heartbeat.

 

Fraggle Rocker; Even though the gen3 nuclear plants like fukushima have advanced safeties in place it is still possible for a catastrophic meltdown. Some of the key safety features of the reactor I have read about are as follows.
1. MSR's liquid fuel is not under pressure. This reduces the risk of explosion and therefore eliminates large containment vessels. In the event of a breach the spill would be localalized and offer a much lower threat to nearby populations.
2. Freeze plugs- These are plugs of frozen salt kept cooled by special electric fans. In the event of a power loss the plug melts and the fuel drains into a holding tank where it will slowly cool much like melted wax. tubes of carbon in the holding tanks help eat up spare neutrons and help in stabilizing the reaction.
3. The fuel loop- The molten salt-thorium solution is pumped through a continous loop through the reactor and heat exchangers. Fission can only occur when the diameter of the vessel reaches six feet. This limits the reaction to the reactor itself.

As for your questions concerning weaponization, as the resultant material is U-233 I believe it would require further enrichment for true weaponization. However I am not an expert on Fission weapons so you may want to check with someone who is.

As far as downsides, there will always be risks when you are dealing with any type of fission reactor but untill we develop true fusion technology I feel that Thorium MSRs are a much better alternative to standard nuclear reactors.

One added bonus is that due to their smaller size and lower potential risk they could be built closer to population centers. This would help reduce energy loss through transmission. Current reactors lose anywhere from 20 to 30 percwnt of their power during transmission.
(note; parts of this response are qouted from popsci mag july 2011)

 

BillyT; Thanks for the extra data.

 

Kinda contradicting yourself there, but to your points:

Well, at that point the fuel is U233 which was produced by the "seed" fissile material, which starts to convert the thorium to uranium. The technical term is that thorium is "fertile" and can easily be converted to a fissile material. In most reactor designs the seed remains in place for years to generate a sufficient quantity of U233 to sustain the reaction.

The reaction is: neutron + thorium-232 -> thorium-233 -> protactinium-233 -> uranium-233. The neutron comes from the seed or a neutron generator. The uranium-233 is a fissile element which is capable of sustaining a chain reaction.

In a properly designed reactor, after a few years there is a sustainable amount of U-233 around the seed which is undergoing fission. This both generates power and provides neutrons to transmute more thorium to uranium.

Right. You accelerate protons and fire them at a target, which neutrons are spalled from.

Right. And we ran the first uranium reactor back in 1942. In 1960, we built commercial strontium-90 reactors to power remote locations (like the McMurdo base) - those turned out to be nightmares. Longevity does not mean "ready for real time."

Agreed. U-235 can also be used to run conventional reactors, and plutonium can be used as MOX fuel in conventional reactors as well.

In a CANDU reactor, 100% of the mined uranium is useful as fuel. It runs on nonenriched uranium.

While I agree with the physics there, a system _designed_ to melt down and breach the reactor may not be so popular. With conventional systems, a leak results in a loss of coolant accident, which in the worst case leads to melting of the core and possible escape of core material into the environment. A thorium reactor almost guarantees it.

That is not to say that you can't design a safe system; indeed, the thorium fuel cycle is overall very promising. But it needs a lot of work compared to PWR/BWR reactors. Just saying "we'll just let the entire core of incredibly hot, incredibly radioactive uranium and thorium fall into a big pan, and let the neutrons escape into the air" isn't a sufficient plan.

Agreed, those are good safety features. Many modern lightwater reactors (like the AP600) incorporate them as well.

Again, I think thorium reactors are pretty promising, and we should be working on them. But they are nowhere near as mature as light water reactors and will take a lot of work to make them even as safe as current reactors.

 

Is there some reason why considerable U235 from dismanted bomb could not make it self sustaining IMMEDIATELY? I.e after the inititial charge only more thorium is added (and accumulated fission products periodically removed)?

Thanks for: "The reaction is: neutron + thorium-232 -> thorium-233 -> protactinium-233 -> uranium-233. The neutron comes from the seed or a neutron generator. The uranium-233 is a fissile element which is capable of sustaining a chain reaction. "

Yes I have liked it for years. I guess the capital cost of the heavy water moderator is why it is not more used. Sure would be nice if enrichment plants did not exist (but that would make nuclear subs nearly impossible as they need small reactors and thus require about twice the level of enrichment that a commercial power reactor does as I recall.) They were a useful deterrent during the insanity of MAD as could stay under water for trips around the world, even.

Why not MORE populare as cheaper and much safer? No meltdown because as the temperature rises above bottom "plug's" melting point, the entire reaction core drains out to a very flat geometry. Gravity, and gravity alone, stop the reaction in a few seconds as now all most all neutrons escape from the new core geometry.

The conventional pressurized boiling water reactor has the reacting uranium contain fuel rods which prevent any geometry change until it melts down everything and do melt down if cool water flow is lost. Meltdowns are impossible in a bottom plug thorium reactor(until gravity ceases to exist).
Furthermore there is no water in contact with the thorium core; however, in conventional uranium reactor water is the coolant. When it over heats, that water (steam) reacts with the zirconium cladded fuel rod to make high pressure hydrogen and explosions that can rupture the already high pressure reaction chamber. There is not even moderate pressure in a thorium reactor and no way to make a hydrogen explosion as core is liquid sodium cooled - no water even near the core.

 

You have to allow enough time for the neutron source to transmute enough thorium to U233 to start a self-sustaining reaction. Since in a MSR you can't rely on the thorium near the seed to _stay_ near the seed you have to create enough U233 in the entire molten salt/thorium mixture.

Once the concentration of U233 allows a fission chain reaction then you can remove the seed.

Well, a mixture of molten uranium, thorium and salt is going to melt through the reactor containment and spread out over a large area. One could claim "well, that's not really a meltdown per se, the core is always melted down" but it would be a hard sell overall I think.

There is of course pressure. No way to avoid that if you assume gravity and pumps. However, it's a lot lower than either a BWR or a PWR.

Well, at some point you have to transfer that heat to a phase change fluid for use in a Carnot cycle engine (i.e. turbine.) In all MSR's I've seen, that phase change fluid is water. So you have molten salt -> sodium -> water as a heat transfer chain.

Needless to say, if the molten sodium ever touches the water in the heat exchanger, the results will be fairly dramatic. Again, manageable I think, but certainly not simple.

 

Two more quotes on thorium reactor:
“…India's Kakrapar-1reactor is the world's first reactor which uses thorium rather than depleted uranium to achieve power flattening across the reactor core.[31]India, which has about 25% of the world's thorium reserves, is developing a 300 MW prototype of a thorium-based Advanced Heavy Water Reactor (AHWR). {Much like CANDU, BT thinks} The prototype is expected to be fully operational by 2011, following which five more reactors will be constructed.

… the best results occur with molten salt reactors (MSRs), such as ORNL's liquid fluoride thorium reactor (LFTR), which have built-in negative-feedback reaction rates, due to salt expansion and thus reactor throttling via load. This is a great safety advantage, since no emergency cooling system is needed, which is both expensive and adds thermal inefficiency. In fact, an MSR was chosen as the base design for the 1960s DoD Atomic Plane largely because of its great safety advantages, even under aircraft maneuvering. In the basic design, an MSR generates heat at higher temperatures, continuously, and without refuelling shutdowns, so it can provide hot air to a more efficient (Brayton Cycle) turbine. An MSR run this way is about 30% better in thermal efficiency than common thermal plants, whether combustive or traditional solid-fuelled nuclear. …”

Some benefits of thorium fuel when compared with uranium were summarized as follows:
(1) Weapons-grade fissionable material (233U) is harder to retrieve safely and clandestinely from a thorium reactor;
(2) Thorium produces 10 to 10,000 times less long-lived radioactive waste;
(3) Thorium comes out of the ground as a 100% pure, usable isotope, which does not require enrichment,…”

From: http://en.wikipedia.org/wiki/Thorium#Benefits_and_challenges

“… Because India is outside the Nuclear Non-Proliferation Treaty due to its weapons program, it was for 34 years largely excluded from trade in nuclear plant or materials, which has hampered its development of civil nuclear energy until 2009. Due to these trade bans and lack of indigenous uranium, India* has uniquely been developing a nuclear fuel cycle to exploit its reserves of thorium. … India has a vision of becoming a world leader in nuclear technology due to its expertise in fast reactors and thorium fuel cycle. ..."
From: http://www.world-nuclear.org/info/inf53.html
------------
*India is rich in thorium, may have one of the world’s largest supplies of thorium. (Cheap electric power for more than a dozen millenniums!)
Billy T comment: Ironically, despite the US operating a thorium reactor five decades ago, the US may import the technology from India!

 

You omitted the important difference. With the geometry change as core spread out in the catch pan, THE CHAIN REACTION STOPS IMMEDIATELY. with no need for cooling, electricity, pumps, etc. ONLY gravity quickly shuts the reactor off. The "China syndrome" with reaction continuing as core melts thru floor into the ground is impossible. (That made a good, but very far fetched movie.)

IMHO, that plus being cheaper, is a huge selling point. It doesn't hurt that there is hundreds of times less less long-lived radioactive waste to store either when selling it. There is still no accepted solution to this waste problem, but it could be orders of magnitude smaller for the same energy production.

 

Quite simple, I think; i.e. that heat exchanger is lower than any thorium, even if it has drained out into the catch pan. Last time I studies the question, water does not run up hill.

True, in small part of the heat exchanger, the water is steam under high pressure, but if a leak were to develop letting H2O cross to the Na side of the heat exchanger, you simply blast a big hole on the steam side of it so water and steam safely vent into a never-occupied, roofless, high-walled "room." (You remove a large, pre-placed, cover with explosive bolts like used to separate the shuttle's booster rockets -very safe and already "man rated.")

Once the pressure on the steam/water side of heat exchanger has dropped to the pressure on the Na side, almost all of the water will have "flashed" into steam and gone out the open roof. There some possibility that Na could come into contact with a little H2O, so there might be a flash fire in that topless "room" but definitely not anything like the strong, containment vessel bursting hydrogen explosion conventional uranium reactors typically have when they fail.

 

Certainly the molten salts I think need way more research funding, but I think the molten lead cooled reactor design is more viable near term.

 

See, this is being entertaining after all.

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Thanks for the info, guys.

 

You seem to still be thinking of a "seed volume" separate from the thorium, whereas I am thinking of a nearly homogenous mixed reacting core.

The utilization of thorium would naturally be higher near the center of the core (Center tends to be hotter but fact it is the slow neutrons that are used may off set some of this.) as fewer neutrons would be escaping from at center than near the edge; however, uneven heating in a liquid tends to mix it well.

BTW, I like ElectricF's suggestion that lead instead of sodium be used if feasible as then there is not even slight chance of a Pb/H20 fire with leak in the heat exchanger. (See last paragraph of post 17 for more on this slight risk of brief, well contained, Na/H20 fire.)

I admit that with four decades more development the uranium reactors are "more mature", but even the first of the thorium reactors look more attractive as much safer, significantly cheaper, and have orders of magnitude less long half life waste problem. Think how much better they will be when they have had a few decades of refinement. Hell in two decades we may have returned to Edison's "no transformers" electric power stations with small thorium reactors in dense population neighborhoods! - But I doubt that as uranium reactors have given nuclear power a bad public image.