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PostPosted: Jul 10, 2013 7:52 pm 
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This report from the Breakthrough Institute evaluates and compares Gen III and Gen IV nuclear power technologies to determine which offer the best prospects for cost reduction in the near to medium term. The report uses four criteria:

- inherent safety
- modular build
- thermally efficient
- high degree of readiness

You can see a summary matrix of the findings on page 9. In short, the salt-cooled pebble bed reactor is the only technology that meets all four criteria. LFTR would then be a likely evolutionary advancement from the PB-AHTR.

This is the development path that Per Peterson has envisioned on this discussion board. In fact, Per Peterson was a contributor to the Breakthrough Institute report and I think his view is well represented. I'm curious if other people share this view of the PB-AHTR and LFTR relationship. Also curious if anyone agrees with the report's technical evaluation of LFTR commercialization challenges. The report says that flibe monitoring and filtering will require a major time-consuming research effort. That's the same opinion David LeBlanc has, but the Breakthrough Report does not evaluate his once-through liquid fuel reactor with offsite filtering.

Part of the LFTR discussion is quoted below, and there are a few more pages about LFTR in the report.

---------------------------------------------------------------------------

How to Make Nuclear Cheap: Safety, Readiness, Modularity, and Efficiency
By Jessica Lovering, Ted Nordhaus, Michael Shellenberger
The Breakthrough Institute, 7 July 2013

Quote from pages 35-36:

Readiness

The PB-AHTR (Pebble Bed Advanced High-Temperature Reactor) was engineered to use off-the-shelf components and the established US nuclear supply chain. The fuel pebbles were created for the gas-cooled, high-temperature reactors described above. The molten salt coolant was designed and tested in fast reactors. The pool configuration is based on the sodium-cooled fast reactor, and its Brayton engines can be purchased off-the-shelf and are widely used in today’s highly efficient natural gas turbines.

While fluoride salt has a large operating range of temperatures, it also has a high freezing temperature (300-500oC). The risk is not meltdown but rather lost capital investment should the salt coolant freeze and seriously damage the reactor. While experience from some initial models suggest that a solidified coolant could have certain benefits, such as sealing in melted fuel or preventing leaks, further testing at different scales and under extreme conditions will be necessary before the design is ready for approval.

The PB-AHTR was engineered to use metals such as 316 stainless steel that have been certified by the American Society for Mechanical Engineers (ASME) — an NRC requirement — for the primary system pressure boundary and structures. Other materials such as Alloy N and molybdenum may be better suited in terms of long-term performance, but it is uncertain how much more testing and characterization these materials need before they can be approved by the ASME and the NRC.

The LFTR brings the advantage of utilizing a liquid fuel, which obviates the need for costly fuel fabrication and cladding, but requires careful monitoring and filtering of dissolved fuel. Technologies capable of monitoring and filtering liquid fuels have not been developed or proven, suggesting that the commercial scale development of the LFTR will likely evolve from the PB-AHTR design if and when the PB-AHTR is commercialized.

The Chinese Academy of Science announced in early 2011 that they would massively scale up their research and development of a molten salt-cooled design and complete a research reactor by 2017.

Bottom Line

Among new nuclear technologies, the PB-AHTR alone meets all of the key criteria identified in this assessment as critical to achieving substantial cost reductions relatively quickly. It operates at ambient pressure and utilizes a fuel and coolant that are not prone to runaway heating or meltdown. It is well suited to be fully modularized. It is largely based on components and materials that have been proven technologically at commercial scale. The PB-AHTR still faces a number of uncertainties, technical hurdles, and supply chain challenges but could be ready for commercialization by the mid-2020s. The LFTR is likely to follow the PB-AHTR into development and commercialization — the LFTR represents both an advancement over the PBAHTR and a potential evolutionary bridge to the commercialization of fast reactors, as its dissolved fuel, pool type, design, and molten salt coolant are features of molten-salt fast reactor designs.


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PostPosted: Jul 10, 2013 8:41 pm 
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Joined: Apr 28, 2011 10:44 am
Posts: 247
Gentlemen,

Here are the facts of life:

1) Flibe does not exist in anything like the quantities we need.

2) The only proven methoid for making flibe is extremely expensive
and an enviromental disaster in the making. See Y-12.

3) Both PB-AHTR and LFTR (understood as a 2 salt breeder) require flibe,
the former in a very highly enriched form.

4), To claim any system that require flibe satisfies "high degree of readiness"
is deep into denial. (BI has lots of company here.)

5) LFTR also requires a barrier material that does not exist.

Molten salt converters require neither flibe nor unobtainium.
It does not require a breakthrough.

I guess that's why the breakthrough institute ignored it.

Jack


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PostPosted: Jul 11, 2013 1:11 am 
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Joined: Sep 15, 2011 7:58 pm
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Quote:
2) The only proven methoid for making flibe is extremely expensive
and an enviromental disaster in the making. See Y-12.

Do a search on these forums. There was a post just about this. Just recently they discovered a method for isotopic separation of lithium that involves some carbon something or others, and does not involve mercury. Looks like that problem is solved.


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PostPosted: Jul 11, 2013 10:41 am 
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Joined: Apr 28, 2011 10:44 am
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Just about every year a new method for enriching lithium is invented
and we jump on this as the "solution". Next year we will probably have
yet another solution. This problem has been solved a half-dozen times,
yet every time a new idea comes along we drop last year's solution.

As fas as I can see none of these ideas, are even close to proven,
let alone costed.
We are in denial.


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PostPosted: Jul 11, 2013 11:39 am 
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Joined: Jul 14, 2008 3:12 pm
Posts: 5056
djw1 wrote:
Just about every year a new method for enriching lithium is invented
and we jump on this as the "solution". Next year we will probably have
yet another solution. This problem has been solved a half-dozen times,
yet every time a new idea comes along we drop last year's solution.

As fas as I can see none of these ideas, are even close to proven,
let alone costed.
We are in denial.


Not entirely fair. There are no molten salt reactors, and the proposed build for test reactors require only a small amount of Li-7. The market is just too small for enrichers to bother with investing even tiny amounts of R&D in it. It's similar to the tritium market today: producing it is easy, but tritium is not in major demand, and in fact is considered an environmental nuissance (unfairly - no one has ever been harmed by tritium).

The crown ether seperation (using lithium crown ether) looks pretty simple and using conventional chemical processes that are used to produce various common chemicals. The liquid extraction technology is widely used by many chemical companies. It does not appear to be unobtainium.

That said, a NaF substitute, like NaF-BeF2, looks pretty simple a change as well. The downside is primarily the research needed to test this new mixture - thermo-hydraulics, trifluoride solubility, chemistry and corrosion control, etc. We should not underestimate this part of R&D effort, which is largely absent with FLiBe. The other advantage that no one talks about is that FLiBe has really good heat transfer properaties, so it's a major gain in cost (size) of heat exchangers, pumps and the like. A much more viscous and lower heat capacity salt would result in bigger pumps, heat exchangers, etc. The systemic cost of this is considerable.

FLiBe is quite attractive for a secondary loop in the design I favor (with a third NaNO3-KNO3 loop). It has no long lived activation and very little short lived activation. If you substitute a cheap low melting salt such as sodium, there's much more short lived activation, making lots of things more difficult - you have a dirty coolant loop as opposed to a clean loop (as eg PWRs have).


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PostPosted: Jul 11, 2013 2:04 pm 
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Joined: Apr 28, 2011 10:44 am
Posts: 247
So if we depend on flibe, we have a chicken and egg problem.
No flibe until we have a market, and no market until we have flibe.

Thanks to ORNL we know a great deal about nabe,
We have ternary phase diagrams for NaF-BeF2-UF4
and NaF-BeF2-ThF4. ORNL really did not start looking
at lithium until it fell inot their laps thanks to the H-bomb.
We have decent viscosity and heat trasnfer and
we know the cross-sections. They are not that much
worse than flibe, and plenty good for a converter.

The remaining uncertainties (eg the quatenary system)
are trivial compared to proving, costing and then scaling up
a lithium enrichment system, assuming one of the candidates
really proves to be economic.

The pebble bed does not have the option of going to nabe
but we do. Thiis is a critically important advantage
which we ignore at our peril.

Anyway the only way out of the chicken and egg
is to start with nabe and a converter.


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PostPosted: Jul 11, 2013 10:47 pm 
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Joined: Apr 19, 2008 1:06 am
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An MSR using FNaBe is a good way to start. In its lifetime, it can produce besides power, a quantity of U-233. The power could be used for producing Li-7 using mass spectrometer via the anode rays or any better technology developed.
It may be worthwhile using excess U-233 and doing without graphite moderator, another bugbear in the thermal design LFTR, in later versions. FNaBe is good enough for fast spectrum. Light water is now used in most of the current nuclear reactors despite the knowledge and limited use of neutron-efficient heavy water for similar reasons. FLiBe and FNaBe could be in MSR alternates like the heavy and light water in solid fuel reactors.


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