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PostPosted: Apr 22, 2013 11:16 pm 
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Ed P wrote:
The KISS principle is great for a first fluid fueled reactor! The more pieces and systems there are, the more things that will give problems in the development and construction. This will help keep things on track better, thus making the reactor look better by staying on schedule and operating. Also, the less systems there are the more easily it keep modular with less pieces to be shipped. Keeping the first heat exchanger in the vessel helps with this as well, as long as the package doesn't get too long to ship by truck.

I too, whole heartedly support your direction David. :-) I hope your concept to do without the graphite works out as well, both to prevent having to change it, and prevent having to deal xenon absorption in the graphite.



Hi Ed,

I know I've worked on and discussed many design options, some with some without graphite but just to be clear the IMSR design I have begun to divulge and discuss does look to employ graphite moderator. I will be keeping core details somewhat under wraps and of course will continue to optimize and explore options but I do favor the advantages that a graphite core offers even though there are drawbacks of graphite. Basically as I've said, the IMSR tries to combine features of the SmAHTR (integral design, salt cooled) and DMSR (Single Fluid, graphite moderated burner reactor). There is more to it than that, but all in good time.

David LeBlanc


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PostPosted: Apr 23, 2013 5:22 am 
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David wrote:
[quote=
I know I've worked on and discussed many design options, some with some without graphite but just to be clear the IMSR design I have begun to divulge and discuss does look to employ graphite moderator. I will be keeping core details somewhat under wraps and of course will continue to optimize and explore options but I do favor the advantages that a graphite core offers even though there are drawbacks of graphite. Basically as I've said, the IMSR tries to combine features of the SmAHTR (integral design, salt cooled) and DMSR (Single Fluid, graphite moderated burner reactor). There is more to it than that, but all in good time.

David LeBlanc


Are you to the point that you are willing to discuss the trade-offs from your perspective of the graphite vs. no graphite, especially if it relates to getting a fluid fueled reactor (IMSR) up and running. I do understand that there are benefits to both sides, but, as indicated, have heard more about the challenges of the graphite.


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PostPosted: Apr 28, 2013 1:13 pm 
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Congrats on your progress David.

I noticed in your 2010 paper for the Canadian Nuclear Society, you said, "It is likely a uranium
only DMSR would require as little as 50 tonnes natural U per GWe year as opposed to 35 tonnes for
the LEU+Th DMSR but still far less than the upwards of 200 tonnes required for LWR or 150 for
CANDU
".

If this is still the case (or even if is uses half the U of a LWR or CANDU for the same electric output) then that is a great selling point. I would not mourn the lack of thorium. It would be a good data point if you could tell people how much this extends the available uranium resource (i.e. how long could such reactors supply all the electricity in the world before the cost went up by 2 cents/kWh due to uranium scarcity?).

Also, focusing initially on the once-thru cycle is good. But it would be better if you could show a plausible road map for adding reprocessing later. Wouldn’t molten salt fuel reduce the cost (per kWh) of reprocessing compared to LWR or CANDU fuel? Wouldn’t molten salt fuel make it easy to guarantee that all Pu-bearing fuel was so radioactive as to be self-protecting (i.e. by adding some dirty salt to freshly recycled fuel).

Another angle to consider is the political sensitivity of the export business. The developed world does not want the developing countries to be tempted to obtain technology for enrichment or reprocessing, nor do we want them stockpiling plutonium (separated or not). If there were an economical way for us to take back used fuel, keep the Pu, Am, & Np here (perhaps to burn in domestic IMSRs or fast reactors), and send them fission product waste in ready-to-bury packages, that would be a great product (I know a startup company can't offer a sophisticated product like that, but the reactor is the key first element). I presume that the used fuel from an IMSR would have less Pu (per kWh) than used LWR fuel?

It looks like the power density will be very good. That will make it easy to put [the reactor - edited] underground; people seem to like that.

An appealing feature of SmAHTR (and the IFR) is the pool design. It is easy for the casual observer to convince herself that the coolant is not going anywhere (i.e. through leaky pipes, faulty drain valves, etc). I think that is even more important with fuel in the coolant, so I’m not really a fan of the dump tank.

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Nathan Wilson, MSEE


Last edited by Nathan2go on Apr 28, 2013 8:26 pm, edited 2 times in total.

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PostPosted: Apr 28, 2013 3:26 pm 
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Nathan2go wrote:
It looks like the power density will be very good. That will make it easy to put underground; people seem to like that.



FRANCE:NUCLEAR
http://www.pbs.org/wgbh/pages/frontline ... rench.html

Things were going very well until the late 80s when another nuclear issue surfaced that threatened to derail their very successful program: nuclear waste.

French technocrats had never thought that the waste issue would be much of a problem. From the beginning the French had been recycling their nuclear waste, reclaiming the plutonium and unused uranium and fabricating new fuel elements. This not only gave energy, it reduced the volume and longevity of French radioactive waste. The volume of the ultimate high-level waste was indeed very small: the contribution of a family of four using electricity for 20 years is a glass cylinder the size of a cigarette lighter. It was assumed that this high-level waste would be buried in underground geological storage and in the 80s French engineers began digging exploratory holes in France's rural regions.

To the astonishment of France's technocrats, the populations in these regions were extremely unhappy. There were riots. The same rural regions that had actively lobbied to become nuclear power plant sites were openly hostile to the idea of being selected as France's nuclear waste dump. In retrospect, Mandil says, it's not surprising. It's not the risk of a waste site, so much as the lack of any perceived benefit. "People in France can be proud of their nuclear plants, but nobody wants to be proud of having a nuclear dustbin under its feet." In 1990, all activity was stopped and the matter was turned over to the French parliament, who appointed a politician, Monsieur Bataille, to look into the matter.

Christian Bataille resembles the French comedian Jacques Tati. His face breaks into a broad grin when asked why he was appointed to this task. "They were desperate," he says. "In France, executive power dominates much more than in Anglo-Saxon countries. So that if the Executive asks parliament to do something it means they are really at the end of their ideas."

Bataille went and spoke to the people who were protesting and soon realized that the engineers and bureaucrats had greatly misunderstood the psychology of the French people. The technocrats had seen the problem in technical terms. To them, the cheapest and safest solution was to permanently bury the waste underground. But for the rural French says Bataille, "the idea of burying the waste awoke the most profound human myths. In France we bury the dead, we don't bury nuclear waste...there was an idea of profanation of the soil, desecration of the Earth."

Bataille discovered that the rural populations had an idea of "Parisians, the consumers of electricity, coming to the countryside, going to the bottom of your garden with a spade, digging a hole and burying nuclear waste, permanently." Using the word permanently was especially clumsy says Bataille because it left the impression that the authorities were abandoning the waste forever and would never come back to take care of it.

Fighting the objections of technical experts who argued it would increase costs, Bataille introduced the notions of reversibility and stocking. Waste should not be buried permanently but rather stocked in a way that made it accessible at some time in the future. People felt much happier with the idea of a "stocking center" than a "nuclear graveyard". Was this just a semantic difference? No, says Bataille. Stocking waste and watching it involves a commitment to the future. It implies that the waste will not be forgotten. It implies that the authorities will continue to be responsible. And, says Bataille, it offers some possibility of future advances. "Today we stock containers of waste because currently scientists don't know how to reduce or eliminate the toxicity, but maybe in 100 years perhaps scientists will."

Bataille began working on a new law that he presented to parliament in 1991. It laid plans to build 3-4 research laboratories at various sites. These laboratories would be charged with investigating various options, including deep geological storage, above ground stocking and transmutation and detoxification of waste. The law calls for the labs to be built in the next few years and then, based on the research they yield, parliament will decide its final decision. Bataille's law specifies 2006 as the year in which parliament must decide which laboratory will become the national stocking center

Bataille's plan seems to be working. Several regions have applied to host underground laboratories hoping the labs will bring in money and high prestige scientific jobs. But ultimate success is by no means certain. One of these laboratories will, in effect, become the stocking center for the nation and the local people may find that unacceptable. If protesters organize, they can block shipments on the roads and rail. The situation could quickly get out of hand.

Nuclear waste is an enormously difficult political problem which to date no country has solved. It is, in a sense, the Achilles heel of the nuclear industry. Could this issue strike down France's uniquely successful nuclear program? France's politicians and technocrats are in no doubt. If France is unable to solve this issue, says Mandil, then "I do not see how we can continue our nuclear program."







MONITOR AND STORE UNDERGROUND. DO NOT BURY. MONITOR AND STORE. DO NOT BURY. PROTECT THE SOIL.


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PostPosted: Apr 28, 2013 7:09 pm 
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NicholasJanssen wrote:
MONITOR AND STORE UNDERGROUND. DO NOT BURY. MONITOR AND STORE. DO NOT BURY. PROTECT THE SOIL.

My suggestion above was to put the reactor below ground level. This is to help protect it from "external events", such as truck bombs and airplane strikes. This is a common design feature with new reactors such as sodium-cooled and salt-cooled reactors (because these reactors are not very tall). Light Water Reactors typically have very tall containment buildings around them, but the new small LWR from Babcock and Wilcox (the 125MWe mPower) promises an underground containment.

But regarding nuclear waste: nuclear waste repositories have nothing to do with soil. We live on the Earth's thin outer layer, with the natural biosphere only extending down a couple of dozen feet. Our fresh water all comes from the top 1000 feet, and the fossil fuels we use come from the top mile or so.

Below that, it's geology (not biology) all the way down, for thousands of miles. The geology area is where mother nature recycles her extra CO2 (by chemically processing rocks) and where she stores her extra radioisotopes (that's where geothermal energy comes from). In the biosphere, a lot can happen in 10,000 years; not so in the geology area. Putting our CO2 and nuclear trash down there is completely harmonious with nature.

With that said, I realize many people are concerned with the safety of nuclear waste storage. The President's Blue Ribbon Commission on America's Nuclear Future devoted a lot of effort to studying public relations brc website archive.

Personally, I advocate eventual adoption of reprocessing used nuclear fuel to reduce 99% of the long term radio-toxicity (but only after we switch to reactors that facilitate this). That way, if we start with 100 or so years of monitored storage (when the stuff is the most hazardous), we can then move it to un-monitored permanent storage with no real risk of something bad happening. But I'm not at all bothered by a few decades of direct burial of nuclear waste, since I believe that our decedents will still be using nuclear power 10,000 years from now, and the waste from our activities will be negligible compared to their own. On the other hand, if our high-tech civilization falls, and our decedents are simple farming people, then they won't be digging any 2000 foot deep holes, so our waste won't get in their way.

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Nathan Wilson, MSEE


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PostPosted: Apr 28, 2013 8:11 pm 
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Nathan2go wrote:
NicholasJanssen wrote:
MONITOR AND STORE UNDERGROUND. DO NOT BURY. MONITOR AND STORE. DO NOT BURY. PROTECT THE SOIL.

But I'm not at all bothered by a few decades of direct burial of nuclear waste, since I believe that our decedents will still be using nuclear power 10,000 years from now, and the waste from our activities will be negligible compared to their own.


Yes. Reprocessing is very important. But you fail to reach out to the common people with such lengthy paragraphs. Constantly monitored storage by professionals is the absolute requirement to promote nuclear energy.

Anytime someone says "buried" or "underground" you will lose people. You must try to use "secured monitored bunker" because then your message will be delivered correctly. Communication is the message received, not the message sent. Talking the right things to the right audience is important.

That particular QUOTE confounds me to no end! Are you silly enough to believe that the future will have more waste than we have now? The OPPOSITE, the future they will dig up our valuable waste and turn it into useful things.


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PostPosted: Apr 28, 2013 9:26 pm 
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Ed P wrote:
David wrote:
[quote=
I know I've worked on and discussed many design options, some with some without graphite but just to be clear the IMSR design I have begun to divulge and discuss does look to employ graphite moderator. I will be keeping core details somewhat under wraps and of course will continue to optimize and explore options but I do favor the advantages that a graphite core offers even though there are drawbacks of graphite. Basically as I've said, the IMSR tries to combine features of the SmAHTR (integral design, salt cooled) and DMSR (Single Fluid, graphite moderated burner reactor). There is more to it than that, but all in good time.

David LeBlanc


Are you to the point that you are willing to discuss the trade-offs from your perspective of the graphite vs. no graphite, especially if it relates to getting a fluid fueled reactor (IMSR) up and running. I do understand that there are benefits to both sides, but, as indicated, have heard more about the challenges of the graphite.



Ed,

The tradeoffs between graphite or no graphite is indeed an encompassing subject and there are likely thousands of posts here discussing it. If you boil it down to comparing a solid moderator free fast spectrum to one with a softer spectrum I think it is very challenging, and more so than some will admit, to bring a fast spectrum design to market (especially in terms of such designs are exceedingly hard to do low unit power and still be attractive). Of course there are lots of interesting gray areas in design that are very interesting and I'd mention that likely the best engineered fast spectrum salt design I've seen is the Russian MOSART design which still called upon using graphite to help protect their vessel from neutron flux so it is rarely a cut and dry issue.

David LeBlanc


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PostPosted: Apr 28, 2013 10:09 pm 
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Quote:
If this is still the case (or even if is uses half the U of a LWR or CANDU for the same electric output) then that is a great selling point. I would not mourn the lack of thorium. It would be a good data point if you could tell people how much this extends the available uranium resource (i.e. how long could such reactors supply all the electricity in the world before the cost went up by 2 cents/kWh due to uranium scarcity?).


Nathan,

Thanks for the comments. Such exercises won't convince skeptics but fun nonetheless so here goes... Even a poor mileage IMSR should get 50 tonnes per GWe Year and the price of uranium would need to be about 3300$/kg to rise the fuel cost to 2cents/kwh. There is a rule of thumb with mineral extraction that each time you double the real price of the commodity (i.e. adjusted for inflation) you get a 10 fold increase in potential resources since you look for more and can now economically mine lower grade deposits. With Uranium at 100$/kg (a lot less at the current moment) the 3300$/kg price represents 5 doublings or potentially opening up 100,000 times more resource so from the current known recoverable resource of 5 million tonnes to 500 billion tonnes.

Here is a great overview of the uranium resource issue.

http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Uranium-Resources/Supply-of-Uranium/#.UX3eA8p8x8o

The entire planets electrical use is about 2300 GWe, if we extend that all the way to 10,000 GWe to cover most other energy use as well then we'd need 500,000 tonnes of U a year. This gives us a nice round million years before the fuel cost starts to even make a dent in the price. I doubt will need these reactors for more than a couple hundred years though so I think we'll be good. By then fusion, di-lithium crystals or some other thing we haven't even imagined yet can take over.

David LeBlanc


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PostPosted: Apr 28, 2013 11:59 pm 
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You could get uranium from sea water for less than 3000$/kg. If you could outsource the reprocessing, you could get cheaper fuel. At least two of the nuclear powers, Russia and China could do it commercially. The US and some other countries find the stocks of SNF a real hindrance to continuation of nuclear power. Thorium is desirable due to superior fissile U-233, but is avoidable or postpone-able.


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PostPosted: Apr 29, 2013 10:14 am 
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Quote:
An appealing feature of SmAHTR (and the IFR) is the pool design. It is easy for the casual observer to convince herself that the coolant is not going anywhere (i.e. through leaky pipes, faulty drain valves, etc). I think that is even more important with fuel in the coolant, so I’m not really a fan of the dump tank.


I like pool design too, though SmAHTR doesn't really use this, it is an integral vessel with the HX in the vessel. I think it's more appropriate for large reactors as they need a big heat sink to dump initial decay heat that can't be easily removed by passive systems. There are many more options for small reactors because of their huge surface area to volume ratio. In a molten salt reactor, coolant going somewhere is less of a criticality issue than with molten salt cooled, solid fuelled reactors. This is because in MSR, the fuel goes out with the coolant. If the reactor sits in a steel lined concrete cavity, then any spillage would make the core subcritical. In stead the issue here becomes decay heat removal and keeping containment, since fuel salt spillage means a big mess goes somewhere.

Because of this, I'm currently doing basic thermo modelling of a water cooled steel plate concrete cavity, which I think is among the most fitting for such a small reactor. Early results are promising, the concrete temp is always below 100 degree C and it's easy to add enough water in a passive thermosyphon loop connected to a big tank, for 1-2 months of boiloff cooling. It is basically walk away safe even with vessel failure plus permanent loss of power plus permanent loss of scram. If the vessel fails the passive cooling just gets better. It is also very compact which suits the application well.

The nodalization schematic isn't very clarifying, so here's a sketch of this option:

Attachment:
PCCS.pdf [57.89 KiB]
Downloaded 179 times


One word of caution though, not to dampen the optimism, but David's design isn't really integral because it still needs steam generators, nitrate salt loops (well at least I think these are needed), and someplace to put the offgas tank that has lots of nasty volatile radioactivity involved. So integral may be a bit unfair nomenclature.


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PostPosted: Apr 30, 2013 1:38 am 
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David,
Thanks for the info in uranium resources. I guess that explains why breeders have not caught on.

But I am still perplexed by the comparison to water cooled reactors. Since CANDUs have similar neutronic efficiency to IMSRs, shouldn't they have similar resource utilization when used with recycling? For LWRs at least, as I understand it, recycling only boosts the energy delivered from the uranium about 20%.

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PostPosted: Apr 30, 2013 3:48 am 
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CANDUs have extremely poor burnup, an order of magnitude lower than IMSR. The IMSR just keeps the fuel in the reactor, adds new fissile to the old gunk, so only a portion that just physically won't fit has to be skimmed off to a holdup tank, whereas CANDU must remove all of the old fuel with a new fuel addition. So while the conversion ratio of CANDU can be as good or better than IMSR, uranium usage is still much higher.


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PostPosted: Apr 30, 2013 11:17 am 
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Cyril R wrote:
CANDUs have extremely poor burnup, an order of magnitude lower than IMSR. The IMSR just keeps the fuel in the reactor, adds new fissile to the old gunk, so only a portion that just physically won't fit has to be skimmed off to a holdup tank, whereas CANDU must remove all of the old fuel with a new fuel addition. So while the conversion ratio of CANDU can be as good or better than IMSR, uranium usage is still much higher.


Yeah, but CANDU has the supreme advantage of not requiring enriched uranium! normal uranium is thousands of times cheaper and than enriched uranium!


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PostPosted: Apr 30, 2013 11:35 am 
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NicholasJanssen wrote:
Cyril R wrote:
CANDUs have extremely poor burnup, an order of magnitude lower than IMSR. The IMSR just keeps the fuel in the reactor, adds new fissile to the old gunk, so only a portion that just physically won't fit has to be skimmed off to a holdup tank, whereas CANDU must remove all of the old fuel with a new fuel addition. So while the conversion ratio of CANDU can be as good or better than IMSR, uranium usage is still much higher.


Yeah, but CANDU has the supreme advantage of not requiring enriched uranium! normal uranium is thousands of times cheaper and than enriched uranium!


I don't think so, cost of uranium and enrichment are more or less similar in today's market, for LWR levels of enrichment.


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PostPosted: Apr 30, 2013 12:38 pm 
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Cyril R wrote:
NicholasJanssen wrote:
Cyril R wrote:
CANDUs have extremely poor burnup, an order of magnitude lower than IMSR. The IMSR just keeps the fuel in the reactor, adds new fissile to the old gunk, so only a portion that just physically won't fit has to be skimmed off to a holdup tank, whereas CANDU must remove all of the old fuel with a new fuel addition. So while the conversion ratio of CANDU can be as good or better than IMSR, uranium usage is still much higher.


Yeah, but CANDU has the supreme advantage of not requiring enriched uranium! normal uranium is thousands of times cheaper and than enriched uranium!


I don't think so, cost of uranium and enrichment are more or less similar in today's market, for LWR levels of enrichment.


The wise uranium calculator shows a fuel cost of around $80M/GWe-yr of which $30M is the future waste management cost and $18M is the conversion (to UF6 + enrichment cost). To a first order I'd guess a CANDU and LWR probably consume similar amounts of natural uranium. CANDU saves on the conversion and enrichment but must fabricate much more (perhaps 6x) fuel and generates much more spent fuel (about 6x). The calculator shows a cost of $12M for fabrication and $21M for future waste management. These presumably would get multiplied up so I'm not thinking a CANDU has a cost advantage for the fuel.


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