Energy From Thorium Discussion Forum

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PostPosted: Aug 30, 2008 7:06 pm 
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Third, get help. The South Africans are developing a pebble bed modular reactor (PBMR). Why reinvent the wheel? At a minimum if INL is not already having these discussions, explore the possibility of a joint effort. The PBMR folks have already committed to building a demonstration 200 Mw reactor. INL's reactor is expected to be about 300 Mw. Unless the engineering approaches are radically different, it looks like an interesting opportunity.


Modularity has always been one of my favorite ideas. Making a big thing from a lot of little things has been the key to success in many fields. For example, the software industry has perfected this concept to a high degree and would not exist in its absence.

If specified properly, a small modular reactor can be the answer to flexible nuclear power. A small reactor has many advantages that are maintained even when it is used in a large cluster.

The super computer built from many PC processors is a standard IT approach these days.

If the interfaces, controls, and outputs are well designed, everything works smoothly, whether it is for a single module or a many module configuration.

With modularity, you can have small, a little bigger, pretty big, and huge, all in one design package. You can power New York City or Smallville all with the same hardware.

The MIT reactor design is my current favorite because of its modularity.

INL should strongly encourage and promote modular design and development of the total range of reactors to avoid the duplication of design, development, custom construction and qualification not to mention unnecessary expense.

For example, turbines, generators, and various types of recuperators and heat exchangers can be qualified and available for off the shelf use.

The INL can maintain a trusted reactor module catalog or library for use by any small reactor developer.

This can be extended to pebble fuel handling systems, tritium removal systems, pebble inspection systems, reactor control systems, including cluster control systems, process heat modules, and a variety of hydrogen production modules.

Modules should be sized to be truck deliverable and factory mass production line buildable.

Each trusted module can be specified by materials use, operating environments and interface/control definitions.

A reactor module manufacturing supply chain will quickly form with one or more trusted manufactures of each trusted module in competition to support the small reactor business.

A molten salt reactor can use many of these common modules if an indirect cooling loop using helium in the secondary loop is adopted in its design.

If the molten salt reactor used 60MM graphite pebbles for moderation many PBMR modules can be used in its design with a large saving in development and certification cost.

This is the time to lay out a good plan to maximize the advantages of small modular reactors.

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PostPosted: Aug 30, 2008 7:16 pm 
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Axil wrote:
If the molten salt reactor used 60MM graphite pebbles for moderation many PBMR modules can be used in its design with a large saving in development and certification cost.

I don't see why that would be beneficial:
PBMR modules are designed to operate under about 1,000 PSI pressure (~70 bars), which makes them unnecessarily expensive for the low-pressure systems of an MSR.

Unless you're just talking about the turbogenerator unit ?

From recent discussion on this forum, it sounds as though supercritical CO2 is a cheaper solution than Helium.....


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PostPosted: Aug 30, 2008 8:18 pm 
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Jaro, I had this post in mind.

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After all, I am just proposing a very short startup period where TRISO fuel is only used to boot strap the thorium nuclear reaction in agreement with David’s plan. For the other 30 - 60 years of operation, just mostly thorium fuel is used. In addition, minimization of the lifetime reactor cost is what will sell in the end to the utilities, all other things being equal.


Axil,

Yes, that mode of operation would have benefit. If the TRISO is only used as a way to burn LEU (Low Enriched Uranium) to boot strap to a pure Th-U233 cycle in the core and blanket salts. It would probably take a more fissile than other startup methods, but LEU is much easier to ship around. You just burn out enough TRISO pebbles until there is enough U233 in the core salt to continue and eventually all pebbles are just graphite (with maybe a Silicon Carbide coating for fire prevention). Probably no attempt at the difficult TRISO reprocessing but this leaves some nasty transuranics wastes in the pebbles though. I have proposed another way to startup on LEU but if a design was going to use graphite pebbles anyway, this would certainly be a possible way to start up on LEU.

The advantages seem to be an even safer and publicly acceptable way to ship out startup fissile material but the main drawbacks are you produce a lot of transuranic wastes that are very hard to process out (for the first few years anyhow). As well dealing with decay heat of the startup TRISO pebbles adds some complication.

David L.

If the MSR can meet the (~70 bars), helium interface between the primary coolant loop of the molten salt and the secondary high pressure helium cooling loop then the MSR can use all the helium based modules including the Brayton cycle' helium turbine generator, the helium based process heat interfaces, and the helium driven hydrogen generators.

If high volume mass production of these helium modules can keep the cost under the cost of a custom built or limited production supercritical CO2 unit then helium might be cheaper.

It all depends on how many high temperature reactors of various types use helium to generate large numbers of helium based modules manufactured by mass production.

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PostPosted: Aug 30, 2008 8:52 pm 
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Actually Axil, the fluoride reactor can use a significantly better approach to the closed-Brayton-cycle than the pebble-bed (gas-cooled) reactor because it can use the hot fluoride salt to reheat the gas successively, improving the net work of the cycle and keeping efficiency high. I have modeled these cycle variations extensively in the Brayton cycle simulator I've built:

viewtopic.php?f=30&t=15


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PostPosted: Aug 30, 2008 9:44 pm 
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Thanks Kirk

I will grant a new supercritical CO2 turbo generator. I hope the increased efficiency is worth it. In a perfect modular world, one type gas should be used in the secondary cooling loop for all reactor types. See what you can do.

As a system engineer, I would now ask if CO2 can be used in the helium based process heat interface as an alternative to helium. If not, then can a secondary helium cooling loop be added and used to drive the process heat unit?

The same questions apply to the hydrogen generator, heat exchangers etc.

The control software must be structured to allow sufficient flexibility to control the MSR without a complete redesign. Control software development is expensive. Some early thinking/lobbying on this can save much money down the line.

My assumption is like the PBMR, the MSR is completely automated.

In modular development, early thinking /lobbying/action bears big dividends.

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PostPosted: Aug 30, 2008 9:47 pm 
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CO2 vs. Helium is one trade, but the modification I mentioned didn't have anything to do with gas selection--it has to do with how you can heat the working fluid successively to increase net work, which leads to smaller turbomachinery and lower system costs.


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PostPosted: Aug 31, 2008 9:00 am 
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in my opinion,

Part of the problem with the clean up contract is that is it is tied to square footage. So you get a lot of perfectly good low risk office buildings and ware houses torn down and replaced with trailers. Some of the buildings on the D&D list have you wonder what people are thinking. i.e. You have a containment building at TAN that would have been perfect to test these reactors were are talking about. A rail road door high bay hot shot with remote crane. a 15 year old chemical storage building at INTEC. A 15 year old robotics building at INTEC. yet, The INTEC process building will not be down this contract ( although it will be almost ready). At the same time you have Battelle needing to use some of these facilities in the future. An example is the MTR reactor building. It has a bunch of offices and labs. old but still usable, which Battelle needs to use. yet the CH2m-hill contact tells them to tear it down. Now Battelle would like new offices and labs but has no money to build them. You have similar problems at CFA. Empty office buildings that could and should be renovated and used. But the clean up contract says to tear them down down.

If you have DOE spilt then they become more indecisive then ever. You have one side eating the "seed corn" of the other side. The tearing down of buildings will have an end here real soon. Once you set something up they do not want to go away. So, what would be their mission? How much of the INL will then be torn down?

I think we need a containment building like the one that came down at TAN. It had a railroad door in it with an over head crane and a control room. tie it into that rail lines at INTEC. This allows you to build a test reactor anywhere. Bring it into the INL on rail car and test it. Once done you take it out and bring in another design. The good thing it does not tie you into any one design.


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PostPosted: Aug 31, 2008 8:29 pm 
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8 years to review a license? Do I see a lack of will on the part of the government. We are talking experimental reactor.

Do you think a small experimental thorium reactor could get built faster?


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PostPosted: Aug 31, 2008 8:45 pm 
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Again, I think there is some confusion about time lines. The NGNP reactor isn't even in the design stage. Until DOE funds that work, and picks one of several possible designs for regulatory review, nothing will happen at the NRC. The NRC review would likely take 3-4 years not 8.

However, you are correct that there appears to be a lack of government will, and funding, for the project.

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PostPosted: Sep 01, 2008 12:01 pm 
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It's hard for me to get excited about NGNP and figure out what it's for.

In an era of expensive fuel, it's even less fuel efficient than a LWR.

If it's intended for process heat, then it needs to be highly portable and it's not.

The hydrogen economy that it is supposedly intended for is going to be an electric economy instead and favor PHEVs instead of hydrogen-fuel-cell cars. Electricity is a whole lot more transmissible than hydrogen.


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PostPosted: Sep 01, 2008 12:26 pm 
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Kirk Sorensen wrote:
It's hard for me to get excited about NGNP and figure out what it's for.

In an era of expensive fuel, it's even less fuel efficient than a LWR.


Why do you say that? The HTR's can achieve much higher conversion ratios than light water reactors and also of course far greater burnup. No to mention they are pretty much the best reactor if you want to get rid of LWR or weapons grade plutonium. Add in the supreme safety and I dont se whats not to get excited about, except the ridiculous timeplan.

It might not be as good as a MSR from a resource point of view, but its closer in time, just as safe and leaps and bounds better than LWR's.


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PostPosted: Sep 01, 2008 12:29 pm 
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If the end goal is a gigawatt-year of electricity, how many tonnes of natural uranium ore does NGNP require vs. an LWR?

Some comparison chart analogous to this:

http://www.energyfromthorium.com/images ... ranium.jpg

With 20% enrichment and no plans for fuel reprocessing I strongly suspect that the numbers will be worse than LWR.


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PostPosted: Sep 01, 2008 1:11 pm 
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Kirk Sorensen wrote:
With 20% enrichment and no plans for fuel reprocessing I strongly suspect that the numbers will be worse than LWR.

Latest numbers I've seen say 9% LEU for the PBMR.
Of course NGNP could be something else.

With LWRs going to ~5% LEU, I'm not sure which one comes out on top.

But I would say that with the TRISO fuel containment, both GT-MHR and PBMR are easily safer than both LWRs and MSRs.

However, I also think that the on-line reprocessing possible with MSRs makes them a worthwhile trade-off, for the additional safety features required to achieve adequate containment & safety.

Using fuel the way LWRs, PBMRs, and GT-MHRs intend to do, is clearly a dead end, as far as uranium resources -- but a good bridging technology nevertheless....


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PostPosted: Sep 01, 2008 2:25 pm 
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Kirk Sorensen wrote:
If the end goal is a gigawatt-year of electricity, how many tonnes of natural uranium ore does NGNP require vs. an LWR?

Some comparison chart analogous to this:

http://www.energyfromthorium.com/images ... ranium.jpg

With 20% enrichment and no plans for fuel reprocessing I strongly suspect that the numbers will be worse than LWR.


I just dug into some articles and it highly depends on fuel type. If it runs on a 15-20% enrichment fuel cycle then your right. The target fuel cycle areva is aiming for with their prismatic block type HTR is a LEU(14%) fuel cycle going to burnups of 150 GWD/ton, 1 ton 14% enrichened uranium needs 33.4 tons natty uranium so 4.49 GWD/ton NU.
With 9.7% enrichment you can get 100 GWd/ton or 4.34 GWd/ton NU.
In a LWR with 5% enrichment and 50GWd/ton you get 4,34 GWd/ton NU. So with regular uranium fuel the difference is negible, I expected it to be better :evil:

With 14% LEU/Th fuel in a pebbled bed reactor you can get a burnup of 78GWd/tonHM. The uranium is 40% of the HM inventory, so 195 GWd/ton LEU or around 5.8 GWd/ton NU. Then its atleast a bit better than LWR.

If using the original german plan to start with HEU/Th fuel, reprocess and use the U-233 then you can get conversion ratio betwen 0.95-1. But the burnup has to be limited to 22 GWd/ton. It will always remain a option though if uranium prices keeps on beeing high.

The smartest thing would of course be to run it on pure Pu fuel or Pu/Th fuel and then it works great in symbiosis with LWR's without needing a gram of uranium. Thats what the russians want to do with the GT-MHR, win-win situation.


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