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PostPosted: Feb 26, 2015 6:44 pm 
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alexterrell wrote:
I've been reading through the documents and some points / questions arise (sorry if repeating):

1. In the Offgas system (Exec summary, page 49):
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Virtually all the 137Xe and 90Kr will have decayed to 137Cs and 90Sr before the offgas leaves the OGR. These two particularly troublesome fission products will not show up in the offgas stream. Rather they will oxidize to fluorides and dissolve into the fuelsalt.


Wouldn't it be better to get these fission products out of the reactor into separate storage? After all, the Offgas system is designed to remove some, but not all, troublesome fission products. Why not get the Cs and Sr out while you can.
[\quote]
Turns out that these have a relatively small capture cross-section so their presence in the fuel salt isn't detrimental to the neutronics. The offgas system will also see a large amount of fuel salt mist so the Cs and Sr are mixed in with fuel salt as they are generated. We could add a demister but then that is another thing to go wrong.
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2. I'm still concerned about the depth of the silos, given the coastal / riverside location for the plants. How about evaluating:
- A six metre high silo hall - high enough for forklift / small crane access to pumps etc, and high enough to allow the secondary and tertiary heat exchangers to be above each other.
- A silo roof build in 8 segments (for a 4 reactor hall) that can slide (similar to some stadium roofs) to expose a can to the crane; or 9m diameter plugs in the silo roof that can be lifted by the main crane prior to can removal.
- A basic 20m high industrial building to house the crane, prevent water ingress, and provide a first layer of (sacrificial) defence to external threats. The silo roof obviously has to withstand the collapse of this building onto it.
Otherwise, I think you'd still need an over building to the keep water out (rain and floodwater, but then cover it in solar panels for a green halio :) )

The silo hall is water tight and can take 10m water on top of it. An overbuilding would add nothing.
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3. ThorCon appears too reliant on manufacturing too much itself. I know it says "everything can be manufactured on a shipyard-like assembly line. But what should be outsourced? ThorCon's strategic advantage is what's in the Silos.

The starter shows:
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Starter 10 GWe/y Yard block diagram, 200,000 tons steel per year

In reality, the first plant is going to be 250MWe - maybe 1GWe. You can't justify a 800mx290m plant for that. So the first couple of Wall/Roof block lines will be bespoke projects - built by a ship yard between two container ships.

The plans are that the initial units will be outsourced to shipyard.
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4. At some point, Thorcon might need smaller, specialist barges. The Big Rhine spec barge http://en.wikipedia.org/wiki/Classifica ... _Waterways has a draft of 3.5m and an air draft of 8.8m, which might just about fit a can of 11.8m height.

Lots of ways to expand once we hit the majority of the market.
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5. The costs don't cover decommissioning. In theory this should be covered by Can recycling costs, but if the cans are not recycled (base case), then it needs to be stored somewhere for 2,000 years. In the UK, nuclear pays a levy to cover this cost (the fund is massively underfunded, but mainly due to weapons, 1950s research, and old reactor designs).

Decommissioning and recycling fuel are difficult areas simply because the political rules are unsettled. There is no good reason why decommissioning should be expensive. We already made the plant modular and can take back to the recycling center all the radioactive parts. But if the government decides to make it impossibly expensive you can drive the price up to preclude nuclear - which frankly appears to be the basic strategy of opponents. You could even end up in the situation where you can't put ultraclean water into the ocean because you can measure some tritium in it. We need to ensure that the host country is more reasonable.
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6. Slide 45 in the "bob_sales.pdf" says looking for nation with
• Industrial capability
• Skilled workforce
• Waterside sites
• Rational regulator

Where's that? UK, Canada, S.Korea, France amongst developed nations? Otherwise China, Turkey, Brazil, UAE (but less IP protection). As I mentioned earlier, the UK's CfD scheme might provide the financial incentive for an investor. There's no reason why "reactor 1" couldn't get a guaranteed £150/MWh for its electricity.

Still hunting for the country. Certainly the guaranteed £150/MWh for electricity (assuming they will take anything close to our full capacity) makes all the finances work out. We still face the hurdle in the UK of being a new technology that needs to be tested and then getting licensed.
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All regulators are fixed on PWR and solid fuel systems, so would need top level pushing to become "rational", which might not happen in some countries.

Undoubtedly some countries will be slower than others in accepting molten salt fueled reactors. Some may never get around to it (witness the lack of Candu's in the US). Developing appropriate regulations is a large hurdle for all molten salt fueled reactors.


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PostPosted: Feb 27, 2015 4:12 am 
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Certainly the guaranteed £150/MWh for electricity (assuming they will take anything close to our full capacity) makes all the finances work out.


Some renewables projects have been bidding for less than that recently:
http://www.theguardian.com/environment/ ... y-projects

Nuclear builds seem to be individually negotiated. For the UK electricity consumer (as opposed to Thorcon or other providers) a good deal would be £150/MWh for the first 250MW, and 75% of that for each subsequent unit (so £150, 112.50, 84, 63 etc.... down to market price).

Ideally (from the consumer perspective), the Government would allow MSR providers to bid against each other. However, the negotiations for this would be intertwined with the regulatory approval, so each nuclear provider is taken on a case by case basis. (Hitachi for example won't be able to agree the strike price for their UK ABWR until they get approval, but there's a feeling for what the price will be - and it will be lower than the EPR strike price.)

There will be some uncertainty up to the election in May. Both main parties are broadly pro-nuclear, but they may have to ally with loony fringe parties.


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PostPosted: Feb 27, 2015 2:39 pm 
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The silo hall is water tight and can take 10m water on top of it. An overbuilding would add nothing.


Fair enough.

In the UK, nuclear build is happening on existing sites. Except in Scotland (they prefer wind and a reliance on England), and Dungeness in Kent.

The Dungeness community would like a replacement for their nuke, but the site is deemed at risk from rising sea levels over the next Century.

A small build like a 1GW Thorcon would be a lot easier to defend against rising sea levels. But - keeping the same silo hall - maybe raise it by 10m? You just have to protect the 10m against aircraft impact - but concrete is cheap.

An overbuilding could add protection against weathering and also allow Can changes to be hidden from view - in case can change overs are a terrorist target.


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PostPosted: Mar 01, 2015 7:17 am 
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Looking at the UK regulator stuff and the ThorCon MSR concept, think a key question will be:

What happens when/if a graphite logs break-up/disintegrate under the neutron bombardment?


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PostPosted: Mar 02, 2015 1:08 am 
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First, we replace the graphite when it has seen 4 years full power equivalent loading. So, if there were no defects in manufacturing then the graphite logs should not break up. However, just in case something does break loose there are screens to keep it from clogging the heat exchanger. The reactor core would need to be taken off line and returned to the recycling center to be cleaned and inspected and a new graphite core inserted.

So a graphite break up would be a financial loss to the owners, and a loss of power to the community, but it would not be a danger to anyone.


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PostPosted: Mar 02, 2015 2:56 am 
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Lars wrote:
First, we replace the graphite when it has seen 4 years full power equivalent loading. So, if there were no defects in manufacturing then the graphite logs should not break up. However, just in case something does break loose there are screens to keep it from clogging the heat exchanger. The reactor core would need to be taken off line and returned to the recycling center to be cleaned and inspected and a new graphite core inserted.



Thanks. Good answer.

Would the power level drop dramatically with the disintegration of one log?

Instead of changing the can out after 4 years, it might then be worth seeing if it can be stretched to 8 years.

If power level drops, then I assume the fuel salt needs to be transferred to a new Can before it solidifies. After a few months fission product decay heat would prevent that. That could however be problematic if a graphite element fails on day 2. I think graphite manufacturing is quite a standard process - but damage in transit may be an issue.

I suppose more likely is a log slab of graphite snaps in the middle, but is held in place by its neighbours. The reactor continues, with a small loss of power, and a slight increase in resistance to flow. The PHX pump motor characteristics will change slightly depending on motor type (increased back-emf, or reduced rpm). Then the computer has the fun game of diagnosing the issue from the data.
Quote:
So a graphite break up would be a financial loss to the owners, and a loss of power to the community, but it would not be a danger to anyone.


So in theory, as long as you can prove that to the regulators, they shouldn't be bothered about the graphite slab manufacturing process. Tick box and move forward 300 pages :)


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PostPosted: Mar 02, 2015 11:03 am 
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IF a log disintegrates the reactor comes off line and goes to zero power. The cans are duplex so we can switch to the other can in a few hours. Each module is 250MWe so if you have a 1GWe plant then you would go down to 750MWe for a few hours and then back up. Currently, there is a window of a few months after we switch from one can to the other where the outage currently would be longer (until the can cools down) - but I bet we figure out a solution to that when we focus more attention to that issue.

A log disintegrating would be cause for investigation - this is not normal wear and tear.

Could we extend from 4 years to 8? It comes down to the graphite. In the center of our core, over the first two years the graphite shrinks 2% due to impacts by fast neutrons (>50keV). From that point on it grows. At four years it is back to its original size. ORNL defined this as the life of the graphite and so far as I know that standard is what everyone has used. It is tricky designing the mechanical arrangement because the graphite changes size both with temperature and with neutron exposure. The temperature varies by 140C from bottom to top and the flux varies 2:1 from the edge to the middle (both radially and vertically) so different sections of the graphite expand different amounts. You do need to be sure that the graphite has room to expand and doesn't get crushed. Also, you can't have any piece that is too large or you will get that kind of crushing forces internal to the graphite and cause cracking.


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PostPosted: Mar 02, 2015 12:17 pm 
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Graphite breaking off is a generic hypothetical accident that considers all graphite moderated MSRs and FHRs.

One thing to keep in mind is that MSRs do not have thermal limits in the fuel. With solid fuelled reactors employing metallic cladding, the blockage of a cooling channel with a piece of debris, can cause cladding overheating. Without this limit MSRs are not very sensitive to debris blocking cooling channels. It generally won't be a safety problem for these reactors, more operational-reliability related.


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PostPosted: Jul 12, 2015 9:51 pm 
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Dr. Hargraves, I have a question about your paper located in the "Documents" section, "Liquid Fluoride Thorium Reactors, An old idea in nuclear power gets reexamined".

On page 305 the article states (emphasis mine)

"The heat and radiation of the reactor core damage the fuel assemblies, one reason fuel rods are taken out of service after just a few years and after consuming only three to five percent of the energy in the uranium they contain."

In the various MSR/LFTR papers, web pages and youtube videos (e.g. Kirk Sorenson and Dr. Joe Bonometti) the point is often made that solid fuel reactors only use up .5%-.7% of their fissile energy. Why is there a difference in the fissile efficiency between what your paper cites and those that cite .5%-.7% fissile efficiency?

Thank you

ETA: Well crap, I didn't realize this was a +year old thread with 11 pages. Sorry if this has already been answered. :oops:


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PostPosted: Aug 08, 2015 12:30 pm 
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I have read the 1.10 version and agree with cheap, simple and quick to build.
I disagree with the idea that a dual fluid solution is impractical unless you have a steel that simultaneously can survive the flouride salt and the neutron flow to the thorium.

One way, which would need to be tested is to do as has already been suggested: use graphite to separate the fluids and accept that there is some leakage between them.
This depends on graphite leaking little enough even as it is aged by a neutron flow.

Another is to use a different geometry: have one pot with the core fluid and another container surrounding the core. Have a low absorption gas on top of the fluids and allow neutrons to bounce the neutrons from the core off a roof into the surrounding fluid. That way the steel can be protected from neutrons by say graphite while still preventing the fluids from leaking. It is more complicated than a single fluid, but perhaps simple enough?
(I don't remember reading this, if it has already been suggested, please tell me where.)

What is wrong with the two pots idea?


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PostPosted: Aug 10, 2015 1:31 am 
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I have not seen a suggestion of reflecting neutrons around the fluid boundary to get to the other side, but I would think that many fewer neutrons could be moved by this method than just letting them pass through the wall.

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PostPosted: Aug 10, 2015 8:21 am 
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Getting neutrons to move should not be a problem as they move somewhat like a gas. Containing them might be. I don't know, someone who understands (soft?) spectrum reflectors might explain?


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PostPosted: Feb 05, 2017 8:15 am 
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FYI, a new ThorCon white paper:

http://thorconpower.com/docs/domsr.pdf


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PostPosted: Feb 05, 2017 11:07 am 
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FTG-05 wrote:
Dr. Hargraves, I have a question about your paper located in the "Documents" section, "Liquid Fluoride Thorium Reactors, An old idea in nuclear power gets reexamined".

On page 305 the article states (emphasis mine)

"The heat and radiation of the reactor core damage the fuel assemblies, one reason fuel rods are taken out of service after just a few years and after consuming only three to five percent of the energy in the uranium they contain."

In the various MSR/LFTR papers, web pages and youtube videos (e.g. Kirk Sorenson and Dr. Joe Bonometti) the point is often made that solid fuel reactors only use up .5%-.7% of their fissile energy. Why is there a difference in the fissile efficiency between what your paper cites and those that cite .5%-.7% fissile efficiency?

Thank you

ETA: Well crap, I didn't realize this was a +year old thread with 11 pages. Sorry if this has already been answered. :oops:


U235 and U238 contain similar potential nuclear energy. By enriching, a lot of U238 (plus a tiny bit of U235) is being thrown away.
The 0.5-0.7% waste includes the Uranium energy thrown away by enrichment. 3-5% includes only the energy extracted vs the original energy in the actual fuel loaded on the reactor.
Consider this:
250 tons of mined Uranium
after enrichment only 35 tons of LEU is made, 225 tons of Uranium becomes depleted uranium which is most useless for now.
of the 35 tons of LEU, about a single ton of nuclear elements gets fissioned (this actually varies if reprocessing+MOX is used and depending on the burnup levels of the reactor, CANDU is the most efficient thermal reactor today, while an old Gen II PWR/BWR does much worse).
1 ton vs 225 tons = .5 - .7% efficiency
1 ton vs 35 tons = 3-5% efficiency

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PostPosted: Feb 05, 2017 12:51 pm 
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With the low price of enrichment 250 tonnes of mined uranium becomes ~135 tonnes of 1.2% uranium.

A CANDU fissions roughly 2% of the nuclei in a 1.2% enriched uranium fuel element.
That means that roughly ~1.1% of the nuclei are fissioned.

Without any reprocessing and using reactors you can phone up the vendor of and order today.


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