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PostPosted: Nov 11, 2013 12:49 am 
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Luke Moylan wrote:
Also an additional question, if you guys don't mind.

In the event of a fuel salt spill in the cell complex of a 2-fluid reactor, the containment buildings would retain the majority of the radiation, no worries. But when the salt cools and solidifies, it produces Fluorine gas, which is very reactive. The Fukushima incident involved the build up of H2 inside the containment structure, which then exploded, because there was no passive filter. Are there current technologies that can passively filter F2?

I can't find any results with a google search.

Thanks!

The fluorine gas generation is not a result of the salt cooling and solidifying. It is the result of radioactive decay reducing the amount of fluorine tied up in that compound (for example changing a trivalent element into a divalent element). It is a decades long process. ORNL warned about this early on that you didn't want to let fuel salt solidify and then leave it for a long time. When they shutdown MSRE they did almost this. They guessed it might work to just warm up the salt periodically. Only decades later did they learn that it wasn't good enough. So moral of the story, if you have a fuel salt spill, clean it up in a reasonable time.


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PostPosted: Nov 11, 2013 12:53 am 
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Luke Moylan wrote:
I'm looking for inspiration from some of the safety calculations performed for the MSRE (I know it's a single-fluid LFTR), and I would like to know if I'm reading this graph correctly.

http://www.energyfromthorium.com/pdf/ORNL-TM-0251.pdf

On page 7, we have a graph representing a fuel pump failure with no corrective action taken. After about 65 seconds we have the fuel reaching a max. temp. of just over 1400 F, which is about 760 C.

Is this indicating that even when left to its own devices, the MSRE was largely self-controlled? This temperature should be within capability of the graphite, and reactor vessel to handle, shouldn't it?

I'm assuming these figures are based on the 235U since the report is from '62. Would there be a significant change when going to 233U?

If we adapt the same scenario over to the 2-fluid LFTR, I'm thinking we'll see a similar response? But if the blanket salt is lost, and the fuel salt has a pump failure, I'm also thinking it won't be as self correcting due to the neutron availability for fission?

Please enlighten me with your opinions.


The Grenoble team did some safety analysis for the neutronics core. Stuff like hypothesized reactivity insertion (like someone screwing up and inserting 3kg of 233U rather than 3kg of 232Th) and showed no problem. They also check the effects of a reactivity insertion without any justification for the amount or speed of the reactivity insertion (due to the lack of a specific design).


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PostPosted: Nov 11, 2013 1:52 am 
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Lars wrote:
The Grenoble team did some safety analysis for the neutronics core. Stuff like hypothesized reactivity insertion (like someone screwing up and inserting 3kg of 233U rather than 3kg of 232Th) and showed no problem. They also check the effects of a reactivity insertion without any justification for the amount or speed of the reactivity insertion (due to the lack of a specific design).


Is that the French team? Could you please provide a link if you know of one?

Thanks!


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PostPosted: Nov 11, 2013 7:57 am 
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Lars wrote:
Luke Moylan wrote:
Also an additional question, if you guys don't mind.

In the event of a fuel salt spill in the cell complex of a 2-fluid reactor, the containment buildings would retain the majority of the radiation, no worries. But when the salt cools and solidifies, it produces Fluorine gas, which is very reactive. The Fukushima incident involved the build up of H2 inside the containment structure, which then exploded, because there was no passive filter. Are there current technologies that can passively filter F2?

I can't find any results with a google search.

Thanks!

The fluorine gas generation is not a result of the salt cooling and solidifying. It is the result of radioactive decay reducing the amount of fluorine tied up in that compound (for example changing a trivalent element into a divalent element). It is a decades long process. ORNL warned about this early on that you didn't want to let fuel salt solidify and then leave it for a long time. When they shutdown MSRE they did almost this. They guessed it might work to just warm up the salt periodically. Only decades later did they learn that it wasn't good enough. So moral of the story, if you have a fuel salt spill, clean it up in a reasonable time.


The bulk of the problem is generation of UF6.
Talking to ORNL guys who were there, they say they were well aware of the problem.
When the molten salt program was shut down, they asked for $50e3 to removed the uranium from the fuelsalt but it was denied.
They are now talking 500e6 to do the job.


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PostPosted: Nov 11, 2013 8:50 am 
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I have a second doctorial thesis (in French) from Dr. Merle-Lucotte with the safety analysis case. If you send me your e-mail I'll send it to you. It is too big to upload. lars@ti.com


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PostPosted: Nov 11, 2013 9:49 am 
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Lars,

Thanks for your offer! Unfortunately I've finished writing the section on safety in my paper, and won't have time to revise it before submission (classic uni student :roll: )

Again, thanks for your offer.

If you have any reliable sources on potential costs, waste production/disposal, or proliferation resistance, I would be very interested to have a look!

Cheers!


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PostPosted: Nov 11, 2013 9:51 am 
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Also thanks djw1!

I saw a video on youtube which said very much the same thing, haha. That's what happens when the higher ups don't listen to the engineers!


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PostPosted: Nov 11, 2013 10:16 am 
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Luke Moylan wrote:
Lars,

Thanks for your offer! Unfortunately I've finished writing the section on safety in my paper, and won't have time to revise it before submission (classic uni student :roll: )

Again, thanks for your offer.

If you have any reliable sources on potential costs, waste production/disposal, or proliferation resistance, I would be very interested to have a look!

Cheers!

Latest I have from Grenoble is "Recommendations for a demonstrator of Molten Salt Fast Reactor"
Fast Reactor International Conference 2013, Paris, France – E. Merle-Lucotte

I also attached the best reference for proliferation resistance from Dr. Forsberg.


Attachments:
fosberg_lftr_antiprolif.pdf [140.72 KiB]
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PostPosted: Nov 11, 2013 10:44 am 
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I'd also like to refer to the world class book on nuclear energy from the late Cohen:

http://www.phyast.pitt.edu/~blc/book/chapter6.html#5

especially the part on the "worst case nuclear accident" is a good read in the context of safety analysis.


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PostPosted: Nov 11, 2013 9:49 pm 
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Lars,

Thanks for the reference. I will be able to integrate some of the information into the relevant section in my paper!
The PR-MSBR is an interesting concept, and perhaps a worthy one if the US develop the technology and start to sell the rights to foreign countries that might not have the best motives.

Unfortunately the article is obviously focused on the single-fluid reactor, which makes adapting the information slightly more difficult. It seems like a two-fluid reactor will always have the risk of fissile material separation, as the fissile material is processed from the blanket salt and put into the fuel salt.

There's an excellent article in a journal that I can access through my uni, "Nuclear energy: Thorium fuel has risks." Unfortunately I don't think you will be able to access it without being a member, or renting it. http://www.nature.com/nature/journal/v4 ... 2031a.html

Either way, it focuses on the fact that thorium is a nuclear material, from which U233 can be bred, and that there are several techniques for doing this inside OR OUTSIDE of a nuclear reactor.

Thus thorium as a resource needs to be monitored by ensuring countries disclose their hot cell locations. If we match this with the Forsberg article, we have a case that the LFTR allows for careful monitoring of thorium resources, assuming information about fuel produced and fuel used etc. is disclosed by the plant, which is information that can be corroborated by assessing the plant's neutronics etc. The waste-side of LFTRs is considerably more proliferation resistant than alternative NPPs.

Cyril R,

Great link that relates to my original question! If I get the time I will 100% squeeze in some sentences based on his assessment of the "worst case scenario."

Thanks to both of you!


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PostPosted: Nov 14, 2013 3:44 pm 
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Just an update for you lovely citizens that were helping me.

I found an MSRE safety analysis, and they had what was know as the 'maximum credible incident'. They thought the worst possible accident would occur if there was a salt leakage, and just enough water to make the maximum amount of saturated steam in the containment cell. The fission products were then supposed to have leaked from the building and through the stack.

For my paper, I assumed the same scenario, but made up a multiplication factor (rookie assumption) based on the mass of fuel salt in a 2-fluid reactor. I didn't include the blanket salt mass in the multiplication factor because most of the fission occurs in the fuel salt, and the continuous processing reduces the fission products from the blanket that could be released by the steam. The result was that the concentration of fission products was 45x greater than the MSRE.

The amount of curies released from such an incident was still 0.18% of that released from TMI. Total inhaled dose would be lethal within 2.1 km down wind (600 rem). Radiation sickness would begin with varying symptoms within 9.5 km (50-500 rem). Maximum emergency doses would be received within 13.5 km (300 rem to thyroid, 25 rem to the bone).

I also noted that such an incident could likely be designed out from inception by the proper use of barrier walls and flow channels for the salt and water (which could come from pump motor coolant and cell door coolant).

Thanks for your help!


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PostPosted: Nov 14, 2013 4:13 pm 
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The old safety analysis were done with too much conservatism. There were all sorts of silly assumptions like "fencepost man"(dose given to someone who just sits in one location 24/7), and very conservative weather assumptions, fission product settling on surfaces, etc. Just changing a few of those assumptions makes the lethality zero. Just one example, a simple filter in the stack would reduce dose in your scenario by over 99.9% (so more like 0.5 rem rather than 600).

More recent best estimate investigations showed the previous analysis to be seriously in error. By orders of magnitude. This is the SORCA, the state of the art reactor consequence analysis.

It should also be borne in mind that the MSRE was an experimental reactor built at a time when passive safety wasn't even a known concept.

Could you post a link to the MSRE safety document? Is it the one in the document repository?


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PostPosted: Nov 14, 2013 4:29 pm 
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I 100% agree with you, and have mentioned the extreme pessimism in many of the assumptions in my paper.

The report was: http://www.energyfromthorium.com/pdf/ORNL-TM-0732.pdf


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PostPosted: Nov 18, 2013 5:17 pm 
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Cyril, nice job on the Wikipedia article! http://en.wikipedia.org/wiki/Liquid_flu ... um_reactor


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PostPosted: Nov 18, 2013 5:44 pm 
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Thank you Robert! Could use some more editing and brevity though.


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