David LeBlanc is a physics researcher at Carleton University in Ottawa, Ontario. He founded Ottawa Valley Research Associates Ltd. to advance molten salt reactor designs. Is an important contributor to the energyfromthorium.com forum and is becoming lecturer on the related subjects of Thorium Reactors.
My approach in design has always been to simplify as much as possible. The DMSR runs on a liquid salt mixture of low enriched uranium and thorium without the need to develop salt processing methods to remove fission products. It is just a very simple vessel filled with inexpensive graphite with no components or barriers needed within the core region itself.Thus it is basically just a larger version of the highly successful Molten Salt Reactor Experiment that ran from 1965 to 1969. The benchmark DMSR design runs at a lower power density than previous MSR designs in order to get a full 30 year lifetime out of the graphite to remove the complication of replacing graphite. It should be noted though, that it is still much higher power density (and smaller) than any other graphite moderated gas cooled designs.The salt is run in batches with the addition of small amounts Low Enriched Uranium to keep it running. After a long run of perhaps 10 to 30 years, this salt is then removed to have an optional one time only processing done, likely at a central facility.At the very least, the contained uranium can be fairly simply removed and reused and there is an economic incentive to do so. It is hoped a nation also performs the harder removal of the other actinides (Pu, Np, Am, Cm) and also recycle these in the next salt batch. This step is not likely to be done for economic reasons but it is the right thing to do environmentally since by doing so the remaining mix of fission products are only of concern for a few hundred years. This relatively short term storage we can certainly have great confidence in as opposed to trusting disposal methods that need to assure things for hundreds of thousands of years. Furthermore, the proliferation resistance of this design is quite likely the highest of any reactor design running or proposed. Molten salt reactors running on the pure Thorium to U233 cycle do have attractive anti-proliferation features but represents the use of highly enriched uranium which many might argue against regardless of added safeguards. The uranium in a DMSR is always denatured with too much U238 to have any worry of bomb use. Like any reactor (even pure Th-U233 ones) there is Plutonium present but it is very difficult to remove and has a mix of undesirable isotopes that make it much poorer than what is currently in Light Water Reactor waste.This mix of low tecnological uncertainty and high proliferation resistance comes at the modest price of needing a bit more resources than a pure Th-U233 cycle. However it is as little as 20 tonnes of natural uranium per GWe-year and small amounts of enrichment (vs 200 tonnes for a LWR).The fuel costs including enrichment are under 0.1 cents per kwh so it is hard to imagine even the pure Th-U233 cycle reaching this since salt processing costs must be covered. Work on pure Th-U233 cycle designs should continue but the DMSR approach seems to offer just way to many advantages to ignore.
This approach for a pure Th-U233 design can get to high total powers, easily several hundred MWe per “tube within tube” but it is also a great approach to run quite small power levels as well. This approach has a completely encompassing blanket salt that catches all the neutrons coming from the fuel salt in the central tube. Thus, unlike most other reactor designs, one doesn’t need to worry about increasing how many neutrons are lost due to “leakage” if trying to make a small, low power core. I should add a note that this approach is not yet patented but is currently progressing fairly smoothly through this very time consuming (and inexpensive) process.
The tube within tube approach works quite well without any graphite at all within the central tube. Other work that looks to remove graphite typically is faced with needing a much higher fissile starting load (how much U235, U233 or Pu). However with an encompassing blanket salt you can run the central salt with a very low concentration of fissile fuel and the salt itself slows down the neutrons quite effectively to give a softer neutron spectrum that has other advantages than just needing less fissile material. More modeling is needed but early indications point to needing only a few hundred kg of fissile material per GWe (1000 MWe) versus many tonnes in other approaches without graphite.
(note: My tube within tube design is a Two Fluid or perhaps 1 and 1/2 fluid design. It can be run with the uranium denatured but it doesn’t offer the same level of proliferation resistance as the Single Fluid DMSR because with a blanket salt a proliferator could simply stop adding U238 to the blanket.)
Isn’t running without graphite a huge advantage?
Running without any graphite would be nice but I don’t think I’d call it a huge advantage.
But there’s still a need for advanced metals like Hastelloy etc?
Yes of course, we need something for the barrier (Molybdenum alloy, Hastelloy, Carbon composite etc) and we’d likely have lots of Hastelloy N for the outer vessel wall and heat exchangers.
That is a bit outside my area of expertise but certainly the regulatory environment drives up the price of nuclear power. It must be noted though that when starting with designs that are inherently safe like Molten Salt designs, the burden on regulators to assure public safety is enormously relieved and in a logical world at least, this should relate to much lower regulatory headaches and added costs.
I think the public will want, and has the right to see ever increasing safety of nuclear operations. Current reactors already have reached extremely high levels of safety but by expensive engineering solutions and the “defence in depth” approach. It does indeed look like the industry is facing a situation of potential customers weighing added safety features like “core cathers” versus somewhat lower capital costs. Fortunately for molten salt designs we are able to offer designs with the utmost in safety to the public in very cost effective ways.
I’m afraid that is too far from my area of knowledge to offer useful comment.
I’m from a mining town and while I admit there are environmental downsides to any mining operations, the benefits to the local and world economies are enormous. Current uranium mining efforts are dwarfed by those for other metals like copper or iron and certainy coal mining. In 2009 there was about 2 Megatonnes of uranium ore mined while 2500 MT of copper ore was mined. We should try to minimize mining but I don’t foresee any “real” problems of significance even if the world chose to greatly increase even conventional reactors that are very inefficient in uranium use.
I certainly think Canada can go its own way and we’ve proven this in the past with our development of CANDU reactors which are a significant portion of the world’s fleet. While the basic public, political, and regulatory environment is arguably much better than in the U.S. the high inertia of our heavy water heritage will be hard to counter at least through AECL itself. However, even molten salt designs can be quite attractive using heavy water. My feeling is that in the long run, graphite or no moderator at all will prove best but it might be our foot in the door to broader interest of the current Canadian nuclear establishment.
Do you mean Uranium as a fissile source? There is a great deal of very useful fissile material (mainly Pu) in current spent fuel. However if we want to build thousands of reactors worldwide we can soon find ourselves with a shortage. We can even run MSRs with only this waste, i.e. no thorium or even U238 to convert to more fuel. In this mode though, we run out very quickly. As simple start charges to start pure Th-U233 reactors we can go much further but it still represents a potential shortfall.
I worded number 8 badly. I was trying to say “Is there any point or is it possible to run MSR’s with other types of fuel (ie uranium only in the salt) or is Thorium so damn efficient that it’s crazy not to use it. Maybe the idea of running a reactor with just uranium is too proliferation friendly?
A uranium only version of the DMSR is something I’m certainly looking into and depending how you look at it, it could be considered even more proliferation resistant than the standard DMSR that uses both uranium and thorium. The reason is that as soon as you have thorium you also have protactinium which you can separate from all the other denatured uranium and wait for it to decay to U233. This has to be weighed against having a bit more Pu in the salt and needing more uranium annually. Having no thorium in the salt has several other minor advantages but such an overview would take quite awhile to explain.
Refurbishment has been adding useful life to many plants, including CANDUs but at some point, and not too far off it just gets too expensive and new plants are needed to replace the plants that are upwards of 40 years old already (60 years is often suggested as a limit)
Current reactors designs are likely a much better choice than more fossil fuel plants and at least more economically feasable that renewables (which should be part of the mix but very hard to see handling baseload demand). Current designs are certainly not cheap and have many unresolved issues but are at least better than the current alternatives.
Yes, I certainly think MSRs will prove the best long term choice. It may be a long time before they are the only type of reactor but they certainly should play a very large role going forward.
Yes, there certainly seems to be a shortage of trained people and it could indeed curtail progress of all efforts. Hopefully the university system can ramp up to help. A good example is the newly formed University of Ontario Institute of Technology (UOIT). Their nuclear program is growing at an exponential rate and shows no signs of slowing down. Now if I can just convince them (and others) to start doing more MSR research…
- The “D” stands for “denatured”—the uranium in the reactor contains too much U-238 to be useful in weapons. The concept also dispenses with processing the salt to remove fission products; the same salt is used throughout the 30-year life of the reactor with small amounts of low enriched uranium added each year to keep the fissile material constant. The amount of uranium fuel needed—about 35 metric tons per GWe year—is only one-sixth of what is used by a pressurized water reactor. . . .
The amount of fissile material needed to start new reactors is also very important, especially in terms of a rapid fleet expansion. The 1 GWe DMSR was designed for 3.5 metric tons of U-235 (in easy-to-obtain low-enriched uranium) which can be lowered if uranium costs go up. A new PWR, by contrast, needs about 5 metric tons, whereas a sodium-cooled fast breeder such as the PRISM design requires as much as 18 tons of either U-235 or spent fuel plutonium. Any liquid fluoride reactor can be started on plutonium as well, but this turns out to be an expensive option, since removing plutonium from spent fuel costs around $100,000 per kilogram
See Charles Barton’s Post called Phoenix Rising May 2005 that covers David’s trip to ORNL earlier this year and where the DMSR was discussed.
Youtube Talks by David LeBlanc
ORNL Talk – May 2010
CONTACT DAVID AT email@example.com