Energy From Thorium Discussion Forum

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JUST ONE LFTR PROTOTYPE WOULD BE A HUGE BOOST

At first glance, those threads look really good. It will take some time for me to explore them thoroughly and perhaps do a write-up incorporating material from them, including links. It should be as narrowly focused as possible on safety and still be sufficiently comprehensive to cover the subject adequately. I hope that I can find material regarding a LFTR that has been operational for a long time.

This is true. John Slough, the man behind this effort, is working to scale up the fusion reaction by increasing the magnetic confinement up to the 10 T field he envisions for a hybrid thorium reactor.

John Slough's philosophy is one that I am sure would appeal to the engineers in this forum. Although it would, of course, be nice to understand what is going on in scientific detail, he doesn't waste time worrying about it. He tries things out, and if it works, he builds on it. For example, they did an experiment where they smashed two FRCs into each other. You might expect that they would squish past each other, or tip, or disrupt, and do any number of deleterious things, but in fact they stopped and stuck, even when the experimenters weren't careful about alignment. I probably would have been so worried about all the bad things that could happen, and maybe even theoretically should happen, that I would never have done the experiment.


It seems to me that this thorium hybrid concept is in disfavor from all sides of the nuclear community , both the fission and fusion community dislikes this approach.

The fusion community wants a steady state device. They have an aversion to pulsed devices. They don't even want a tokamak reactor to power up and down in a 24 hour cycle, although that would probably make a lot of sense.

They like machines that make a big bang even less. Pulse power puts strain on the reactor structure. You have to pay a lot of attention to cycle fatigue and arcing and all.

But if that's where the physics leads you, good engineering and experience will probably let you make a home there. John is thinking in the 10 Hertz range and a natural fusion power level like 10 MW, but there may be a lot of freedom to choose your operating point. With thorium as a fusion energy multiplier, the hybrid power heat output will be a few hundred times that level.

At this time the design goal is to get to fusion breakeven i.e. ”Q = 1”. IMHO, this is good enough for a successful thorium hybrid. The next step is to get the fusion people up to speed on all the off the self advancements that will have occurred on thorium fission reactors like AHTR and LIFE.




The design goal of 10e17 neutrons per second per pulse is very possible to achieve. At 100 pulses per second, that gives 10e19 neutrons per second total fluence. Over a short time span of a few months, that will build up a working inventory of U233. When enough U233 is produced, the neutron production rate from fusion can be decreased to sustain a steady state hybrid reaction… say down to a fusion pulse rate of a few pulses per second or less. The hybrid will produce heat and power all through this U233 buildup phase, however.

After U233 buildup, lowering the neutron steady state rate produced from fusion will extent the working lifetime of the fusion first wall proportionately.





What is eliminated is the 5% U235 Light Water Reactor fuel in the core of a two fluid Lftr as a neutron source. Because U235 must be denaturized by IAEA rule, there will always be U238 to deal with. In easy to acquire light water reactor fuel, 95% of that core salt is U238. It is this U238 that produces all the transuranic waste.

You say “Some of the uranium fails to fission and generates plutonium, americum, and californium.”

In a pure thorium fuel cycle, only a trace of PU239 and higher waste products are generated.



I see the core of this type of fusion hybrid as an easily replaceable diamond pipe that holds vacuum. This tube runs down the center axis of a long cylinder enclosing the liquid thorium blanket salt; a tube in shell configuration if you please.

The fusion accelerators are at either ends of the diamond tube well out of the region of fission and are easy to operate an maintain. These two accelerators shot T-D plasma down the evacuated diamond tube to and adjustable point of fusion anywhere down the entire length of the long diamond tube.

By adjusting the timing of the pulses from the two counter-facing plasma accelerators, the point of fusion can be moved along the entire length of the diamond tube where no one tube location is used more than another in a ware balancing strategy. This will greatly extend the life of the first wall.




In a thorium fission reactor, the breeding ratio is very tight. One of the design risks on a thorium reactor is that it may not always achieve a breeding ratio greater than 1 due to unexpected loss of neutrons. Adding additional Light Water Reactor fuel to provide the possibility of supplemental neutrons may always be needed.

Clearly getting from a breeding ratio of .95 to 1.01 is a disproportionate cost and design expense that a low cost fusion neutron source can eliminate. The adjustable fusion source can be turned on and off as needed to keeps the hybrid reaction going. For example, there is no pressing need to aggressively remove waste from the hybrid to save neutrons. Keep the solid waste in the reactor until they stabilize, and then remove them.



This type of FRC fusion can burn deuterium exclusively in a pure D-D fuel cycle. But if some tritium is produced in the fission process, then burn it. No harm done.



Laser Inertial Fusion Engine (LIFE) at the the National Ignition Facility (NIF), will be the test case. We will see.

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The old Zenith slogan: The quality goes in before the name goes on.

It takes somewhere between 500kg and 5000 kg fissile for a 1 GWe LFTR.
If we assume a middle number of 2000kg, and if we grant that he achieves his goal of 1e17 neutrons per pulse and that the system can be pulsed at 100 Hertz and that you capture all the neutrons in a fertile -> fissile conversion with none lost then it will take 16.4 years to get your first load. Buying u235 is cheaper. Yes it comes with u238 and we do need to work around that either by saving the u233 from the blanket and swapping out the fuel or by evolution of the fuel. A true two fluid approach would work well for this. Given that we don't have a solid answer for the startup conditions we should keep this on the table but I think it is not the likely path to generating a startup charge. For startup charge I'm thinking 20% LEU plus (depending on politics at the time) spent fuel Pu. While it is certainly harder to get 20% LEU it appears to be feasible and we only need it to start.


In the pure thorium LFTR you will produce around 20kg Pu per GWe year. I consider this much more than trace amounts. If we recycle the Pu then we can get it down to a much smaller level (I estimated < 100g Pu/GWe-yr) but there are politics involved with building the skills to remove the Pu from the spent fuel. I'm leaning toward not building this capability into each reactor but rather having a central station that takes the spent fuel and separates out the Pu.

You talked about 10MW as the power level of the fusion reaction. Can you quantify the expect flow of neutrons into the molten salt?

The breeding ratio for LFTRs vary from somewhat below breakeven (a single fluid, denatured reactor) up to 16% (though I think this won't be achievable in real life). I'm not sure just how much it will cost to do sufficient processing to break even. I'm not thinking it will be all that much when we are done.

If this is 95% fission LFTR with a litium based salt then you will have tritium produced in sufficient quantity to require care. Solvable but no different for ADS or standard LFTR.

Accelerator design and costs do not revolve around large unknowns, we've been building them for most all of the last century. For reliability you'd probably want some redundancy, but we aren't talking about pushing the state of the art here, and even in high-end research accelerators it is generally the target sensors and data systems that dominate the price of the system more than the accelerators.

No need for apologies, I can relate!



So that's a given? That we are basically starting with a basic LFTR setup with little or no substantive design and cost differences?


"beyond the current state of the art" how so?


I'm quite sure that no one envisions that a human hand must always man a literal on/off switch. The idea, however, is that you run a subcritical system which can achieve criticality only with an outside injection of thermal neutrons. If you have the potential of runaway reactions, then you have a poor or improper subcritical design. Now if you are imply that it is impossible to design such a system, or that it is extremely difficult and costly to implement such a system, then that is a separate argument, and one that should definitely be explored further.


Any proper nuclear core design will incorporate fail-safe features regardless of whether it is a critical or subcritical core design. The issue of an on/off switch isn’t in whether or not such is actually what happens, or even whether or not such is a reliable or best-means-approach for reactor shut-down. The issue of an on/off switch is the general public perception of control and security that it conveys. Now it might be possible to come up with an explanation and argument that destroys or invalidates that public perception, but you aren’t going to replace it with explanations about passive thermo-regulation design features. I’m talking about taking advantage of public opinions and perspectives (regardless of their basis in fact), in a manner that pushes our common nuclear power advocacy, rather than what many seem to see as techno-babble infighting that does little aside from arming the anti-nuclear advocacies with arguments against nuclear power.

Agreed, specifically with the actinides burn-up issue, many reactor types can accommodate a system to “process” this type of waste (regardless of whether or not they are actually deriving any useful energy from the process) and it may be good PR to start trumpeting this as a means of “dealing with the nuclear waste problem.”
Most people are coming around to the problems with other types of energy, I believe that we can focus on the positives and save the problem issues for actual debates with the proponenets of other energy sourcing. Coal is a big baddy, diesel/fuel oil would come second on my list and NG would tail-end the list. I can probably tolerate some NG usage, at least in the near term, but eventually we really need to get away from open-cycle combustion as an energy generating system.

Interesting, though I don't think its an issue that people haven't taken it seriously, but rather that the advocates are the only ones really interested in that approach, and nuclear power advocacy isn't likely to catch fire in an age that largely holds much of science in disdain and contempt.

In response to the John slough system being inferior to LFTR.

If John Slough can deliver then his fusion transmuter hybrid might be available as early as 2012 for $30-40 million in development while a LFTR would take longer and cost more. It was noted that it would take 16.5 years for the fusion transmuter to produce Uranium 235 needed. However, if each module only costs $20-30 million then $300 million for ten modules would cut the production time down to 1.65 years. Nuclear reprocessing plants currently are very expensive. $20 billion for the Japanese Rokkasho reprocessing facility . Five hundred fusion transmuter modules would cost about $15 billion (and the price could go down with factory mass production).

http://nextbigfuture.com/2009/12/develo ... y-for.html

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http://nextbigfuture.com
Coal kills 300+/day and fossil fuel pollution 1000+/day and is a major contributor to climate change. Nuclear power is needed until coal and oil are eliminated.

I confess to being out of my league managing multi-hundred million dollar developments (the largest I've done is around $10M).
But as I read John Slough's information I don't see a full reactor prototype in the plans at all - even at the $40M level.
This is a good thing for his credibility since I don't believe one can develop a reactor for this amount of money.

I based my cost estimates on ORNL's projections (updated to today's dollars). I don't understand where all the money goes - but I know that I don't know what it takes to develop a new reactor so I depend on their estimates.

His second stage diagram ($2.5M) shows a hoped for production of 5e14 neutrons per pulse - which is 1/320,000 th of the neutrons per second in a 1GWe reactor. I don't expect him to build anything scaled for a 1GWe reactor for $2.5M but you should be aware there is still a long way to go yet for him.

If in 2012 he can achieve the neutron production he hopes for (his ?800 pulses/sec and 1e16 neutrons per pulse) would be a major accomplishment. (Unless I made a dumb math error this would mean the fusion machine provides around 5% of the neutrons for the reactor). One still needs to develop the fission reactor. You have no power gain until the fission reactor is added. The question is whether the addition of 5% of the neutrons from a fusion reactor somehow reduces costs for the fission reactor OR enables new operating modes.

In another Helion Energy presentation which I have at the link already presented (updated) They are saying that 50 Helion Fusion engines could burn, transmute all of current US stockpiles of nuclear waste (unburned fuel) in 20 years.

The already presented graph of Helion energy being in the cost sweet spot - expand the chart and see on the left that they have cost estimate below $100 million for their fusion engine. Ballparking $30-70 million.

50 times $100 million ( a high side estimate)- $5 billion is far cheaper than waste repositories or reprocessing.

Double it for "balance of plant" ballpark. double it again for extra margin. $20 billion but faster to get to and does more than
the Rokkasha plant.

If the 2012 unit is not the fully ready thing, based on the timelines it could be 2-4 years more to get to a useful commercial system.

Say 2016.

the $2.5 million proposal looks like ARPA-E size or government stimulus fundable thing. Plus U of Washington gets enough in its regular physics budget to pay for it.

Still faster than development of a LFTR.
Potentially faster and cheaper than building a repository. (especially with regulatory and political issues)

Just the transmutation part even without the dedicated fission reactors would be worthwhile. I think they could transmute fuel for some of the regular reactors now to use

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http://nextbigfuture.com
Coal kills 300+/day and fossil fuel pollution 1000+/day and is a major contributor to climate change. Nuclear power is needed until coal and oil are eliminated.

The claim for 50 fusion engines to consume the entire US stockpile in 20 years is based on a Sandia report
http://fti.neep.wisc.edu/pdf/fdm1307.pdf

In this you will find that in addition to the fusion neutron source supplying a small percentage of makeup neutrons one must also:
separate the actinides from the spent fuel
develop a lead cooled, fluid reactor
develop a first wall material that can survive being in the center of a fast reactor
develop on-line fission product removal.

All these things are not included in Helion fusion engine development program and in fact will require more development work than LFTR. LFTR has the advantage of being similar to MSRE and hence has much development work already completed. I don't believe anyone has built a lead cooled, fluid fuel reactor yet at any size.

One of the biggest challenges with LFTR is the lifetime of the first wall. In our case, that first wall is on the outer perimeter of the reactor chamber where it sees around 5% of the neutrons. In the reactor proposed in the paper above the first wall is between the fusion and fission reactors. It sees the full neutron flux from the fusion machine (and those are very fast so they more damaging to the wall). In addition it is near the heart of the fission reactor where it will see a large fission neutron flux.

This is not to say he should stop work. Solving the energy problem is a very high value proposition worthy of several parallel efforts. But you will not have a power producing reactor for $40M using this approach. He hopes to build a fusion engine with break even power for this money scaled to supply 1/20th the neutrons used in a 1GWe reactor.

You still have the expense of developing the fission reactor - that is not included in any of his costs. The fission reactor is the one that supplies 95% of the neutrons and all of the output power available to sell.

If aneutronic B11-H fusion is not practical from either a technical or economic standpoint anytime in the near future, then D-T fusion is best served by a fusion/fission hybrid concept, and the Hilion reactor topology is well positioned for this approach.

Any big project should be developed in well thought out, mutually supportive and orchestrated phases. The thorium fusion hybrid should conform to this type of development strategy. The first phase should be the development of a U233 fuel factory. The first market would be existing Light Water Reactors and the new AHTR pebble reactors.

The price for the U233 would be well below the current U235 equivalent price. I think that such a fusion/fission fuel factory is very price competitive and is capable of producing U233 very well below this current $70 lbs yellowcake equivalent. The price of yellow cake has varied from $15 to $137 per pound recently and currently it is about $70 per pound.

http://www.osti.gov/bridge/servlets/pur ... 90-JB2FXN/

The best type of fusion/fission hybrid has a very small zone of fusion preferably a point source. The Hilion reactor has this very important feature and because of the small size of the fusion zone it facilitates an all inclosing blanket with almost perfect closure. Because of the ideal efficiency of its almost perfect liquid blanket envelope, I can see this type of subcritical reactor producing about 5500 kgs of pure U232/U233 per year. Very few neutrons would be wasted. Beryllium in the blanket would almost double the production of the fusion neutron flux. To maximize U233 production, no lithium should be included in the blanket. Tritium would come from the waste flow of its dependent parasitic fission reactors; its customers.


The reactor does not need heat exchangers of turboelectric generators; it can dump the heat produced by fusion (typically 10 megawatts) to the air so a thermal power circuit wound not need to be developed or deployed. Because it is subcritical, it would not need a containment structure either.

If the protactinium is removed from the liquid fluoride beryllium/thorium blanket through on-line blanket salt reprocessing immediately after its creation, no fission heat would be produced by U233 fission.

Since this hybrid does not need to produce electric power or connect to the grid, this hybrid can operate intermittingly to allow frequent change out of its first wall. Such a diamond pipe can be replaced in a matter of hours. A coating of lithium hydride on the inside of this first wall diamond pipe might greatly reduce alpha particle damage.


I believe that this is the development strategy currently envisioned for the Helion fusion engine development program.

If the U233 can be produced with a 1% or greater U232 content, then no U238 denaturing would be required by IAEA rules. This highly enriched and proliferation proof U232/U233 nuclear fuel would make light water reactors and AHTR very clean and eliminate the waste problem associated with the uranium fuel cycle. This alone would be a big selling point for the thorium/fusion hybrid and get the thorium fuel cycle off at a run.

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The old Zenith slogan: The quality goes in before the name goes on.

The best suggestion for a U233 factory may be a neutron economic PHWR/CANDU using slightly enriched uranium and thorium in Radkowsky seed and blanket system.

Recently I read an article detailing safety concerns about reactors. Per the article (and this would not apply to LFTRs or ADS), an accident could cause the fuel in the core to become rearranged so that it would have a positive temperature coefficient which could make it impossible to shut the reactor down. The article writer saw that as a serious design deficiency. Can that be a problem and, if so, is there a good solution for it?

You are mistaken in that a core rearrangement event would have any effect on a liquid fuel reactor.

If you are talking about thh solid graphite moderator assemblies in a LFTR somehow failing in such a way as to cause a restart event, remember that the graphite moderator and fuel has to maintain a critical geometry. If this built in geometry is damaged it is not very credible that it would fail in such a way as to cause a recriticality, the tolerances are too precise.