Energy From Thorium Discussion Forum

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PostPosted: Sep 06, 2013 3:07 pm 
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http://www.reddit.com/r/askscience/comments/1luupt/askscience_ama_ask_a_molten_fluoride_salt_lftr/

-Iain


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PostPosted: Sep 06, 2013 3:31 pm 
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Is this Todd Allen at the University of Wisconsin?


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PostPosted: Mar 06, 2014 4:24 pm 
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Ed Lyman + a UCS colleague and a journalist nuclear AMA on Reddit today; various posts ask about LFTR / MSR, all waved away by the hosts (shocking)

http://www.reddit.com/r/science/comments/1zpsxh/were_nuclear_engineers_and_a_prizewinning/

Reddit user zerocool1 (MSR-expert AMA host in link Iain posted) chimes in a couple times, those posts are worth reading, the rest, um, mostly no, not so much.

Last note, UC Berkeley Nuclear Engineering Department supposed to be doing a Reddit AMA sometime next week.


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PostPosted: Mar 06, 2014 5:01 pm 
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Kirk Sorensen wrote:
Is this Todd Allen at the University of Wisconsin?

No, this is Brian Kelleher. He did his PhD on FLiBe, corrosion and the like.

If you're interested: http://www.scribd.com/doc/162086939/PhD-Thesis


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PostPosted: Mar 17, 2014 12:37 pm 
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Per Peterson and UCB nuclear engineering colleagues AMA on Reddit is here: http://www.reddit.com/r/science/comments/20b7v9/science_ama_series_were_professors_in_the/


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PostPosted: Mar 17, 2014 5:33 pm 
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MSJ, thanks for the notification. For the sake of convenience, I'll paste here some of the most interesting responses by Per Peterson.

Quote:
The thorium fuel cycle has clearly attractive features, if it can be developed successfully. I think that most of the skepticism about thorium emerges from questions about the path to develop the necessary reactor and fuel cycle technology, versus open fuel cycles (uranium from seawater) and closed, fast-spectrum uranium cycles.

The most attractive element of the thorium fuel cycle is the ability to operate sustainably using thermal-spectrum neutrons. This allows the design of reactor core structures that use high-temperature ceramic materials like graphite, which have substantial thermal inertia and cannot melt. Because these ceramic materials also provide significant moderation, it is difficult to use them in fast-spectrum reactors and thus the most plausible fast-spectrum reactor designs need to use metallic structural materials in their cores.

So thorium reactors are compatible with higher intrinsic safety (cores which do not suffer structural damage even if greatly overheated) and that can deliver heat at higher temperature, which enables more efficient and flexible power conversion.

Molten fluoride salts are compatible with these high-temperature structural materials, and given their very high boiling temperatures make excellent, low pressure heat transfer fluids. In the near term, the largest benefits in using fluoride salts come from the low pressure and high temperature heat they can produce. This can be achieved with solid fuel, which is simpler to work with and to obtain regulatory approvals.

But molten salt technologies also have significant challenges. One of the most important is managing the much larger amounts of tritium that these reactors produce, compared to light water cooled reactors (the quantities are closer to what heavy-water reactors, such as the CANDU, produce, but methods to control and recovery of tritium are much different for molten salts than for heavy water, and key elements remain to be demonstrated).

Quote:
Question: Why you would want a molten salt reactor, given online reprocessing (protactinium extraction and isolating it for a few half lifes) would make it a massive proliferation risk. Simply increase your reprocessing rate(ie the ratio of fuel in isolation vs in the core and you would get weapons grade U-233. Why is this not always listed as a showstopper?

Per Peterson: In discussing the security of nuclear fuel cycles, it's important to differentiate between physical security and proliferation risks.

Physical security involves preventing the theft by terrorists or criminals of nuclear materials that might be credibly used to fabricate crude nuclear devices, and is a responsibility of the nation that regulates nuclear energy. All advanced fuel cycle technologies that recycle plutonium together with minor actinides provide large barriers to theft, not because the recycled fuel is extremely radioactive, but because it is sufficiently radioactive that it must be handled remotely in heavily shielded hot cells that can be designed to provide large, passive barriers to entry and theft of the material. This contrasts to fuel cycles that use separated plutonium or highly enriched uranium, where the materials have low radiation levels and the containers are contact handled.

U-233 is a quite unattractive material for a nation to select to use for proliferation, due to the high gamma radiation released by a daughter isotope of U-232 which always occurs at some concentration with U-233. But because it is credible that it might be used, it is important that thorium fuel cycles be subject to the same safeguards monitoring by the IAEA as other fuel cycles, to provide timely detection of any effort to divert the U-233 from the fuel cycle.

Quote:
The high melting temperature [of fluoride salts] is both a problem and a benefit. The extremely high boiling temperatures of the salts (>1300°C) that assure low-pressure operation would not exist unless the freezing temperature was also relatively high (the same applies to lead and lead-bismuth cooled reactors). Moreover, for FHRs we use pool-type reactor vessels, and if a reactor vessel ruptures, it is good that molten salts do not want to leak through any cracks that might form in the reactor cavity wall, because they freeze and plug these holes.

Quote:
But there is another important market failure that affects nuclear energy and is not widely recognized, which is the fact that industry cannot get patents for decisions that the U.S. Nuclear Regulatory Commission makes. For example, there are major regulatory questions that will affect the cost and commercial competitiveness of multi-module SMR plants, such as how many staff will be required in their control rooms. Once the first SMR vendor invests and takes the risk to perform licensing, all other vendors can free-ride on the resulting USNRC decision. This is the principal reason that government subsidies to encourage first movers, such as cost sharing or agreements to purchase power or other services (e.g., irradiation) make societal sense.


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PostPosted: Nov 09, 2014 1:26 pm 
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Mr. Sorensen had a Reddit AMA about two years ago wherein he mentions providing power to a military facility within five years. He was hoping for Redstone Arsenal. What is the status of that project? Are we closer to the goal than at the time of the AMA?

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PostPosted: Nov 09, 2014 1:35 pm 
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It is on hold pending an administration more favorably disposed towards such things.


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PostPosted: Nov 09, 2014 4:12 pm 
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Kirk Sorensen wrote:
It is on hold pending an administration more favorably disposed towards such things.


So be sure to vote and choose wisely.

Would it be too far off topic to ask why Redstone Arsenal was chosen as the site for this LFTR experiment? Is it merely because of the proximity to Flibe Energy headquarters?

I read through the discussion quickly and I'm a bit disappointed that the use of MSRs to dispose of existing nuclear waste wasn't given much thought. I guess I can see why, the problem of getting the reactor running in the first place is a much more interesting problem and also required before discussing the problem of how to use spent fuel rods and fuel for the MSR.

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