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PostPosted: Apr 20, 2009 1:52 pm 
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The Lawrence Livermore National Laboratory has announced a follow on Fusion Fission Reactor Project that it suggests could dramatically reduce the nuclear waste "problem".

https://lasers.llnl.gov/missions/energy ... ture/life/

LIFE would couple a scaled down Inertial Confinement Fusion Laser Driven fast neutron generator with a sub-critical Molten Salt Fission Reactor that could burn a wide variety of fission fuels including uranium, plutonium, thoriam, and spent nuclear fuel.

Many participants on the Forum have looked at using a combination of LFTR and LCFR to generate abundant power with very little high level nuclear waste. LFTR reactors start out producing less TRU and generate mostly fission products. LCFRs could potentially burn up the what small amount of TRU is generated by LFTR reactors and reduce dramatically the amount of material that would have to be placed in a long term Yucca replacement repository.

Does anyone know how a small ICF neutron source would compare with a LCFR in terms of the efficiency of burning up TRU and spent nuclear fuel?

LLNL really needs a follow on large program to keep the Lab alive, particularly if the Obama Administration want to curtail any additional strategic weapons work. Could a combination of hundreds of LFTR reactors serviced by a couple of LIFE fusion-fission reactors fill the same role as LFTRs serviced by a smaller number of LCFRs?

If only a few LIFE engines have to be built to handle the reduced TRU waste flow from LFTR reactors it might not matter as much that LIFE, requiring a large laser and expensive carefully produced fusion fuel, is more expensive than LCFR to build and operate.


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PostPosted: Apr 20, 2009 2:29 pm 
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This is a question of the chemical processing not the reactor type.
Any LFTR design that recycles all the actinides will eventually fission all actinides except those that escape the chemical processing.
If can do what we think we can do I do not understand the gain from adding a fusion component to any of the reactors.

Without fusion I think we can burn up as much of the actinides as we can chemically separate from the fission products.
We estimate this to be around 100 grams of actinides / GWe-yr.

Sure could use more bandwidth on getting LFTR built rather than the fusion.


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PostPosted: Apr 20, 2009 3:00 pm 
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Charles W. Forsberg of the Oak Ridge National Laboratory has published the following:

Since the 1950s there have been multiple proposals for MSRs using chloride salts. Recent studies in France have begun to provide an understanding of the characteristics of a chloride salt. The French concept is called REBUS22 and uses a classical plutonium fuel cycle with trichlorides of uranium and TRUs dissolved in the sodium chloride: that is, 45 mol % (U + 15.6% TRU)Cl3 + 55 mol % NaCl. Natural chlorine (composition: 75.4% 35Cl and 24.6% 37Cl) is used. The use of a chloride salt, with its higher atomic number, results in a harder neutron spectrum.
Two major advantages are associated with the use of this type of salt. The higher breeding ratio enables a breeding ratio significantly greater than one with relatively small rates of salt processing required to remove fission products because higher equilibrium fission product loading is allowed in the salt. The million tons of depleted uranium in storage could provide the fuel after the initial fissile loading.

However, there are major challenges: (1) a significantly smaller knowledge base for corrosion resistant materials in chloride salts compared to fluoride salts, along with a somewhat more complex salt chemistry7, 23; (2) a higher fissile inventory relative to other MSR concepts; (3) higher melting points of the salt; and (4) the choice of what chloride salt to use. REBUS uses natural chlorine with 75.4% 35Cl and 24.6% 37Cl 24.6%. In the fast-reactor spectrum, 35Cl captures 5 times more neutrons than does 37Cl. Furthermore, the 35Cl generates 36Cl, a long-lived radionuclide that complicates waste management. Thus, there are major neutronic and waste management incentives to use isotopically separated 37Cl, as part of a longer-term MSR concept.

The simplest and most cost effective waste burner is a once through fast spectrum unmoderated MSR that uses fluoride salt rich in sodium. Such as reactor can achieve a burn up as high as 99.9%

IMHO, I don’t think that it is cost effective to add lasers or repeated reprocessing to such a efficient liquid fluoride once through waste burner to get to 100%.

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PostPosted: Apr 20, 2009 4:31 pm 
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Do you have some reference for achieving 99.9% burnup with NO processing?


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PostPosted: Apr 20, 2009 5:31 pm 
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Lars wrote:
Do you have some reference for achieving 99.9% burnup with NO processing?


viewtopic.php?p=16136#p16136

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PostPosted: Apr 20, 2009 8:23 pm 
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This reactor has fission product processing just like LFTR.


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PostPosted: Apr 20, 2009 9:25 pm 
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Lars wrote:
This reactor has fission product processing just like LFTR.


The once-true reference (i.e. Based on ADNA Tier-1 (Bowman) was for and accelerator driven system. My reference was for a system with reprocessing.

My previous post should read as follows:

The simplest and most cost effective waste burner is a fast spectrum unmoderated MSR that uses fluoride salt rich in sodium. Such as reactor can achieve a burn up as high as 99.9%

IMHO, I don’t think that it is cost effective to add lasers to such an efficient liquid fluoride waste burner to get to 100%.

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PostPosted: Apr 20, 2009 10:48 pm 
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There is no need for LIFE; LFTR can do what LIFE proposes for a lot less money and technical risk.


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PostPosted: Oct 04, 2009 1:05 am 
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Dr Ehud Greenspan likes LIFE and TRISO fuel.


Ehud Greenspan
Department of Nuclear Engineering
University of California


Personal views on hybrid reactors

this white paper was submitted to the Fusion-Fission Hydrid Workshop of September 30, 2009, is to express my views on the preferred application for and approach to the design of hybrid reactors and to inform the new generation of hybrid reactor researchers of the hybrid reactor data base developed in the seventies and early eighties.

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PostPosted: Oct 04, 2009 3:24 am 
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Problem of neutron source for the Ignition Facility for burning up the actinides has not yet been solved. How about using an existing source of high energy neutrons-the fast fission core? This could easily be controlled by positioning a part of the core shaped as a cylindrical piston moving inside the remaining annular cylinder.
Shall it be possible to use these neutrons as a trigger for multiplication and burning of actinides? Shall the neutrons have enough energy for triggering a multiplication?


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PostPosted: Aug 07, 2010 5:19 am 
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jagdish wrote:
Problem of neutron source for the Ignition Facility for burning up the actinides has not yet been solved. How about using an existing source of high energy neutrons-the fast fission core? This could easily be controlled by positioning a part of the core shaped as a cylindrical piston moving inside the remaining annular cylinder.
Shall it be possible to use these neutrons as a trigger for multiplication and burning of actinides? Shall the neutrons have enough energy for triggering a multiplication?


Fission neutrons don't have enough energy to do things like n,2n in large quantities. Beryllium is the only thing that comes close at reasonable neutron energies but even then the n,2n mutiplication is tiny for neutrons born at 2 or 3 MeV. Since beryllium moderates it will bring the neutron energy down to well below the n,2n threshold.

If you have very fast neutrons, from deuterium-tritium fusion for example, most of the heavier elements will have a tendency to do n,2n and sometimes even some n,3n. Lead and bismuth are good, U-238 even better since it also fast fissions and neutron capture will result in more fuel. The cool thing about such heavy elements is that they keep neutron energy very high so you might get a serious fast fission and/or n,2n bonus. There are at least three major problems though:

1. Fusion is complicated and expensive, so assuming access to very fast fusion neutrons is rather reckless.
2. Fast neutrons are good at destroying your reactor. The heavy elements have to be put in some sort of container, which will get destroyed sooner rather than later.
3. The secondary neutrons have much lower energies (not a problem for a heterogeneous reactor though).


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PostPosted: Aug 07, 2010 10:36 am 
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Thanks. Still people including Bill Gates are working on travelling wave reactor, employing a travelling fast fission core.


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PostPosted: Aug 07, 2010 11:30 am 
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Sure, the travelling wave reactor has neutrons born at 2 or 3 MeV, much less damaging than 14 MeV D-T fusion neutrons. Bill Gates won't get himself a lot of n,2n though. But above 1 MeV fast fission of U-238 is very significant. Same for the fertile Pu isotopes - they have significant fast fission x-sections. The fissile isotopes (odd numbered) are typically better the slower the spectrum, but even their fast fission x-sections aren't trivial. If you can keep your neutrons from getting moderated, fast fission will be very nice. Slow neutrons are better at breeding Pu though. One of the reasons heterogeneous designs are intriguing. Get more neutron budget from fast fission, breed and burn more with thermal fission. IF the LIFE thing works, it might be a good synergy with Jaro's HW-MSR, but its all very doubtful if you ask me.


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