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PostPosted: Mar 29, 2010 9:03 pm 
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Introduction


I have made an initial proposal for a revised version of the The Aqueous Homogeneous Reactor(AHR).



That proposal was born upon the prudence to consider the AHR through the lens of a forward looking vision and frame that vision within a context of current technological possibilities, rather than being needlessly constrained by the fixed and out mooted restrictions and limitations imposed by the technologies of the distant past.


In those times long past, The AHR was supplanted by the MSR. In those days, such a decision may have held some merit.


Over these many years since the prototype of the AHR was first tested, many new and exciting technologies have matured and can be repurposed to improve the design of this type of reactor. In my opinion, this accelerating march in technology especially in chemistry can be much more impactful to the AHR design as applied to the pure thorium fuel cycle than anything that can be applied to the MSR.


Many passive safety and fissile breeding features and benefits are advantages that the AHR brings to the table demanding in all prudence a second look.


Their self-controlling features and ability to handle very large increases in reactivity make them unique among reactors, and possibly safest. At Santa Susana, California, Atomics International performed a series of tests titled The Kinetic Energy Experiments. In the late 1940s, control rods were loaded on springs and then flung out of the reactor in milliseconds. Energy output shot up from ~100 watts to over ~1,000,000 watts with no problems observed. The take away: the AHR boosts a have very high neutron flux that are easy to manage.


New technologies can mitigate its various long standing disadvantages. In fact, new cutting edge technology can make the AHR a prime reactor development candidate.


I would like to examine these technologies that have recently sprung from work done in fusion, nano-sono-chemistry, material sciences, and hydrogen storage research.


What motivates this rehabilitation of such an old idea framed in a modern context?


Advantages



First the advantages; in its design and operations, the AHR can provide a breeding ratio with a wide margin of design safety. Like the MSR, the AHR is self-regulating with the fission products continuously removed from the circulating fuel.


But unity breeding in the MSR is a close thing. Not many design tradeoffs can be made against the MSR breeding ratio. It doesn’t take much to push the MSR into a breeding downslide collapsing into sub-unity either in terms of design or operation. Take away: it is so very easy to push the MSR into a sub-unity breeding mode.


As an illustrative example, in a recent post, Rebbat states as follows:


Quote:
“From my personal preference, I would rather design reactors with a high unity gain;
in fact, from a breeding standpoint, a ratio of 1.3 or higher. The reason why is
very simple, such a high ratio would allow me to breed extra fissile, stored in salt,
for the maintenance periods. I can see these periods requiring me to drain the
reactor of spent fuel salt. And flush it with clean salt to increase the safety factor
of my workers. I'll need that extra fissile for a fresh start up.”


Also, I could run such a reactor in pure burner mode. The option to breed would
simply be an option.



I agree with this. Rebbat must be thinking about some sort of AHR design. An Lftr approach can never reach a ratio of 1.3 or higher it is just not in its nature.


Second, if you must suffer the presents of IAEA resident inspectors who are overlooking reactor operations in the reactor complex, it should be at least worthwhile. A descent fissile productivity margin should be the reward for the regulatory aggravation, not a meager .01% over unity.



Third, a high breeding ratio means that there will be far fewer neutrons wasted to degrade the reactor barriers and heat exchangers.


Next, a deep thermal neutron spectrum will breed and burn U233 in an optimum fashion. The fluoride reactor is best in the epithermal neutron range; the natural home for the uranium fuel cycle.


Using Plutonium or U235 is a misapplication in the AHR. U233 is the proper fuel for a deep thermal breeder.


Design Issue Mitigation


Let us now look at how current technology can remove some of the downsides from the original AHR design.


Many of these downsides are centered on the use of heavy water as a moderator/coolant. It is the central roll of this water that makes the AHR an aqueous reactor.


One major limitation on the AHR was its low operating temperature and associated low thermodynamic efficiency and the associated very high pressure vessel operating pressures. This of coarse is due to the physical limitations of its moderator and coolant; heavy water.


With the use of a heavy water moderator also comes corrosion problems and the propensity of water to decompose radiologically (due to fission fragments) releasing gas bubbles have been a perennial design problem.


This radiological decomposition is also expensive. Two percent of the heavy water is destroyed each year and the cost of its replacement is substantial.



So the basic design question to ask is why bear the burden imposed by heavy water when it can be easily replaced by a more capable and stable moderator/coolant. There has been a great deal of very recent work in hydrogen storage systems that can bear fruit for the AHR design. Many new and exciting hydrides have recently been discovered with very high hydrogen content that can easily replace heavy water.



The failures in the hydrogen storage systems are the winners in the new AHR technologies. The hydrides that strongly bind hydrogen and have high temperatures for thermal decomposition are of little use for those interested in hydrogen storage systems since they want hydrogen to be stored and released easily; the more easily the better; but very strong hydrogen retention is of great utility for use in the AHR when deuterium replaces hydrogen.


Lithium hydride is the hydride that has very strong hydrogen retention properties and a high hydrogen vapor pressure. LiH liquefies at 700C and retains hydrogen under limited pressure all the up to 1000C and beyond. So lithium-7 deuteride is a great replacement for heavy water in the AHR to get its operating temperature and efficiency up and the reactor vessel pressure down.
See figure …Lithium Hydride temperature profile…below.



Lithium is a great coolant. I believe that the fluorination of lithium is a coolant design compromise to enable the chemical solubility of uranium in FilBe. Pure lithium is a far superior reactor coolant than FilBe is. Lithium can carry lithium-7 deuteride in an AHR coolant/moderator approach.
Chech out the following figures for a comparison of pure lithium against FilBe… Lithium Thermal Coductivity…and…Lithium Specific Heat…below.


As an interesting aside, the use of lithium-7 deuteride opens up the possibility to use an emerging power conversion device that directly transform nuclear radiation from fission into electricity.


This new concept that Liviu Popa-Simil and Claudiu Muntele devised is based in innovative application of nanotechnology. They are constructing tiles that can be assumed to be shaped to form a sphere around a radiation source. The tiles are made from carbon nanotubes, which are packed with gold with the assembly then surrounded by lithium hydride. The action is in the radiation crashing into the gold that in turn releases a shower of high-energy electrons. The electrons exit into the lithium hydride that harbors electrodes to permit the electrons to form a current that will flow out of the device. Popa-Simil says, “You load the material with nuclear energy and unload an electric current.”



Transforming the energy of radioactive particles into electricity is twenty times more effective (up to power density of 1 kw/cm^3) than thermoelectric materials. It will be big impact when it is commercialized which they expect will be ten years or more.


This new thermonuclear approach holds the promise to work at the temperatures for power plants and could double the efficiency of nuclear power.

See for past opinions:

http://energyfromthorium.com/forum/view ... &sk=t&sd=a


For the latest design details also see

Code:
United States Patent Application   20100061503
Kind Code    A1
Popa-Simil; Liviu    March 11, 2010


http://appft.uspto.gov/netacgi/nph-Pars ... 0100061503

Why should all those alpha particles that are born in the lithium coolant and moderator weaken the AHR reactor barriers when they can be shielded and directly converted to electric power?

The new AHR would be an ideal platform for the application of this sort of direct power conversion.


The next post in this series will deal with sedimentation prevention and vessel burn-through


Attachments:
Lithium Specific Heat.jpg
Lithium Specific Heat.jpg [ 162.2 KiB | Viewed 3150 times ]
Lithium Thermal Coductivity.jpg
Lithium Thermal Coductivity.jpg [ 167.36 KiB | Viewed 3159 times ]
Lithium Hydride temperature profile.jpg
Lithium Hydride temperature profile.jpg [ 125.19 KiB | Viewed 3153 times ]

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PostPosted: Mar 30, 2010 3:03 am 
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Multiphase reactions such as gas/solid, gas/liquid or gas/liquid/solid are widely used in today’s chemical, petroleum and biological processes. Some examples of such reactions are production of cyclohexanol/cyclohexanone from cyclohexane and Benzoic acid/benzaldehyde from toluene by DSM, production of styrene via MBA by Arco, oxidation of propylene by Aristech, Fischer-Tropsch synthesis by SASOL, and hydro-cracking, hydro-isomerization processes by many petrochemical companies.


The AHR can follow this chemical industry technology for multiphase reactors: mainly the Stirred tank reactors (STR) and the Slurry Bubble Column Reactors (SBCRs). In the latter, the solid phase consists of fine catalyst particles, which are suspended in the liquid phase due to the gaseous reactants introduced into the reactor from the bottom often through a sparger. These reactors are becoming more competitive with and are replacing fixed bed reactors due to their inherent chemical engineering advantages:


    • Higher reaction rate per unit volume;
    • Better temperature control;
    • Higher online factor;
    • Higher effectiveness factor;
    • Lower pressure drop; and
    • Higher gas holdup and mass transfer rate.

All the chemical engineering advantages listed above for the SBCR are also important for good AHR nuclear performance and elimination of AHR wall corrosion and reactor vessel burn-through from slurry sedimentation.


The design and scale up of a SBCR approach requires, among others, precise knowledge of the kinetics, hydrodynamics, and heat as well as mass transfer characteristics of the slurry.


More precisely, liquid and solid side mass transfer coefficients, phases holdup, flow regimes, pressure drop, and axial as well as radial solid distributions are fundamental parameters for modeling, design, and scaleup of such AHR reactor designs. Furthermore, the hydrodynamic and mass/heat transfer coefficients should be prototyped under actual reactor operational conditions since high pressure (possible 10-80 bar), high gas throughput, large reactor diameter (5-8m), and high slurry concentration (30-40 vol.%) may be needed in order to describe and quantify a large scale AHR design.


Even through this slurry technology is complex in terms of parameters, it is also well understood and amenable to computer modeling.


The effective slurry design will maintain a uniform homogeneous small gas bubble flow with the highest possible concentration of solid slurry particles.

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PostPosted: Mar 30, 2010 5:20 pm 
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One of the interesting and most useful properties of the Aqueous Homogeneous Reactor (AHR) is the fission recoil separation effect (FRSE).

When fission occurs, the product isotopes of the fission are almost always blasted out of the particle into the surrounding liquid suspension medium. It is highly unlikely for the fission products ruminants will reenter or physically recombine with the slurry particle population. The fission products form a particulate suspension separate from the original slurry.

In the AHR, the fission process physically separates its waste products and it is only necessary to sort them out.


This is the main reason why AHR are favored in the production of radio isotopes.


Undoubtedly, this method can present some advantages and better yields for the production of Mo-99 and other short lived radioisotopes, since they have to be extracted from a liquid in which practically no uranium is present.


One of the basic ideas on these suspension reactors was to apply the fission recoil separation effect as a means of purification of the fuel: the non-volatile fission products can be adsorbed in dispersed active charcoal and removed from the liquid.


IMHO, FRSE can be used to provide a waste removal capability that no other form of fission can support. This solution centers on a slurry/waste particle analysis and control procedure that can now be developed base on the laser ionization mass analyzer.


Background

The laser ionization mass analyzer, LIMA, was originally developed as a bulk microprobe instrument giving elemental information similar to that obtained from the conventional electron probe microanalyser, but with the advantage of full periodic table coverage. The LIMA is therefore capable of detecting all elements including hydrogen, helium, lithium, and beryllium. Other advantages of LIMA are isotope discrimination and the ability to obtain chemical information from materials as a result of the emission of complex ionic fragments from surfaces under laser irradiation.

Image

As experience grew with the use of the prototype LIMA it became clear that the technique was a particularly versatile tool which could not only perform well as a bulk microprobe, but with suitable experimental procedures could also be used as a sensitive depth profiling instrument with moderate depth resolution ( 0.01 m).


In detail, LIMS operates by removing ions from the sample using a microfocused high-power density laser beam, and then analyzing the mass of these ions. The removal of material for analysis is accomplished in one of two laser irradiation modes: 1) by laser desorption (LD); and 2) by laser ionization (LI).


Once the ions are removed from the sample either by LD or LI, the ions are subjected to analysis using a mass spectrometer of time-of-flight design, wherein the mass values of the ions are quantified based on their transit time across a high vacuum region through which they are accelerated by an electric field of known value.


Laser ionization produces ions from the specimen during the vaporization of the material with the laser beam. LI therefore operates under high irradiance levels of more than 1010 W/cm2, and can sample well into the bulk of the specimen. For instance, LI analysis can sample depths on the order of 1000 to 2000 angstroms per laser shot for GaP.


On the other hand, laser desorption can only produce ions from the specimen surface or from substances that are adsorbed on the specimen surface because it operates under relatively low irradiance levels of less than 109 W/cm2. LD sampling depths are on the order of 100 to 200 angstroms per laser shot.


Typical applications of LIMS as a microanalytical tool include: 1) bulk microanalysis of conductor and insulator materials; 2) surface analysis of thin films, contamination, and adsorbed elements and molecules.


The main advantages offered by LIMS is its high elemental sensitivity, wide mass analysis range, and relatively small beam diameter (1 to 5 microns). Because of these, LIMS can distinguish between the bulk material, the materials that are just adsorbed on the surface of the specimen, and materials incorporated in a matrix.

Application

A portion of the slurry particles can be removed from the slurry stream as the coolant carrier is on its way to the heat exchangers.


Using LIMS, it will be possible to examine each particle in the slurry individually one at a time for its elemental composition, size, and isotopic content. This information can be matched against an element and particle specification, sorted for isotopic composition to determine if it should be returned to the slurry, sent to protactinium storage, or resigned to the nuclear waste pile sorted by element.



High isotopic purity is not a requirement of this process. Small light partials are generally waste products and large heavy particles are slurry. The element/isotopic resolution of this process should be kept low.



Heavy elements (thorium or greater) goes back into the reactor, light elements stay out and go though more chemical processing.



After the particle is characterized by the LISM process and exits that section of the column, as the particle is flying through the LIMS reaction column, a directing electric field can be applied to divert it to the appropriate particle exit cavity. The timeframes required to examine the volumes of particles processed per unit time that are necessary in this process are nanoseconds or less.


The amount of slurry/waste material processed per day should exceed 100 Kg/day.


This sort of processing has already been applied in mass in the examination the droplets in a fine aerosol one droplet at a time. As follows:


Quote:
Epstein, Hila; Afergan, Eyal; Moise, Tamar; Richter, Yoram; Rudich, Yinon; Golomb, Gershon, 2006, “Number-concentration of nanoparticles in liposomal and polymeric multiparticulate preparations: Empirical and calculation methods,” Biomaterials, 27(4):651–659

The actual number of particles in formulations of nanoparticles (NP) is of importance for quality assurance, comprehensive physicochemical characterization, and pharmacodynamics. Some calculation methods that have been previously employed are limited because they rely on several assumptions and are not applicable for certain preparations. Currently there are no validated experimental methods for determining the particle number-concentration (Nc) of liposomal and polymeric nanoparticulate preparations (<500 nm). This study examines a new empirical method for counting the number of particles in nanoparticulate formulations including drug-containing liposomes and polymeric NP. In the new method, suspended NP are nebulized to form aerosol droplets which are dried and counted using a scanning mobility particle sizer (SMPS). Experiments were conducted with three different preparations, empty liposomes (200 and 400 nm), drug-loaded liposomes (200 nm), and polymeric NP (150 nm). It was verified that no detrimental morphological or structural changes of the formulations have been induced by the SMPS technique, and that the obtained Nc values represent the original particles. It is concluded that nano-formulations with concentrations of up to 107 particles per 1 cm3 air, corresponding to approximately 1012 particles per 1 ml solution, can be directly counted within the size range of 30–900 nm. The measured values are compared to newly developed theoretical calculations to assess the viability of these calculations.

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PostPosted: Mar 31, 2010 4:06 am 
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Uranium (including U233) is soluble in the form of uranyl salts while thorium salts are less soluble. Suspended particles of thorium is one of the possible solutions but I think easier and more economical solutions are possible. I have suggested a 3-D grill of thorium metal or metallic wool. Most of thorium can stay in place and fissile uranyl salts can be in solution. Heat transfer will be through steam leaving solutes including the uranyl salts fuel in the core.
Pressure of steam will have to be maintained in the reactor vessel but highly soluble BeF2 can be used to operate the reactor at reduced pressures for given temperature and also to moderate the neutrons in a smaller volume.
U233 created closer to the metallic surface can be dissolved in the fuel solution by adding oxidisers. Solution fuel is even easier to process for removal of neutron poisons than the liquid salt based fuel. Reactivity can be controlled by raising or lowering a fraction of thorium absorbants.


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PostPosted: Mar 31, 2010 2:20 pm 
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Reference:

http://www.rsc.org/chemistryworld/News/ ... 031001.asp


Image
The thorium compound is the first 15-coordinate complex (orange: Th, beige: B, purple: N, black: C, blue: H)


Recently, a new record breaking thorium hydride has been discovered: thorium aminodiboranate, Th(H3BNMe2BH3)4. A central thorium atom is bound to 15 separate hydrogens. This compound is so new that it does no yet have an application. But, this exotic thorium compound could find a natural home in the blanket of an Aqueous Homogeneous Reactor (AHR). When formulated with deuterium, a fast neutron from fissioning U233 would have a hard time getting through all that deuterium without being well moderated. The vapor pressure of this new compound promises to be very high, so the blanket temperature in which it floats could sustain high temperatures. Such a thorium hydride makes heavy water look poor in comparison.

This very stable new compound could be fabricated into a slurry grain and floated in a pure lithium carrier. Such new and exciting possibilities make a second look at the AHR redesign a prudent decision.

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PostPosted: Apr 01, 2010 1:23 am 
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Axil wrote:
Reference:

http://www.rsc.org/chemistryworld/News/ ... 031001.asp


Image
The thorium compound is the first 15-coordinate complex (orange: Th, beige: B, purple: N, black: C, blue: H)


Recently, a new record breaking thorium hydride has been discovered: thorium aminodiboranate, Th(H3BNMe2BH3)4. A central thorium atom is bound to 15 separate hydrogens. This compound is so new that it does no yet have an application. But, this exotic thorium compound could find a natural home in the blanket of an Aqueous Homogeneous Reactor (AHR). When formulated with deuterium, a fast neutron from fissioning U233 would have a hard time getting through all that deuterium without being well moderated. The vapor pressure of this new compound promises to be very high, so the blanket temperature in which it floats could sustain high temperatures. Such a thorium hydride makes heavy water look poor in comparison.

This very stable new compound could be fabricated into a slurry grain and floated in a pure lithium carrier. Such new and exciting possibilities make a second look at the AHR redesign a prudent decision.

Its just so that you'll need 11B for Boron, 15N for Nitrogen and Deuterium for Hydrogen. I guess it can be done but I'd prefer Uranyl(U233) salts and solid thorium.
I would also use heavy water only if light water or a solution of BeF2 does not give an acceptable conversion ratio.


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PostPosted: Apr 01, 2010 4:15 pm 
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I think Axil gets the prize for the most imagination on this forum.


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PostPosted: Apr 01, 2010 5:44 pm 
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robert.hargraves wrote:
I think Axil gets the prize for the most imagination on this forum.



"The only way of finding the limits of the possible is by going beyond them into the impossible."

Arthur C. Clarke

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PostPosted: Apr 01, 2010 9:57 pm 
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One of the letters in the acronym “Lftr” stands for the use of fluorine in the liquid fluoride thorium reactor; so fluoride is one of the legs of the thorium three legged platform. But lately, even at the risk of heresy (if I can beg up front forgiveness), this use of fluorine seems to be the cause of far more problems and costs than it is really worth. That leg is weak and stunted.


In detail, fluoride means the use of expensive and as yet unproven super alloys of nickel.


Fluoride means uranium and fluorine corrosion which precludes most cost effective nuclear construction materials.


Fluoride means FilBe which constraints the reactors neutron spectrum to the epithermal range.


Fluoride means that the structure of the reactor will take a beating from fast neutrons.


Secretary of energy Chu when asked about the Lftr first brings up corrosion as an issue.


The one great advantage that the Aqueous Homogeneous Reactor (AHR) has over the MSR or the Lftr is that the AHR does not use fluoride. It can be rapidly built with currently available low cost tried and true nuclear code approved structural materials. And the AHR can be a true thermal breeder reactor.


The AHR can take a page out of the PB-AHTR play book.


Recapitulating some past wisdom, Per Peterson has said as follows:


Quote:
At Berkeley one of the principle reasons we've been focusing toward fluoride-salt cooled, pebble fueled reactors is that the technical issues for materials corrosion, component in-service inspection….



Pure lithium is even less corrosive and easier on reactor structural materials than “clear FilBe”. The use of expensive and exotic nickel isotopes (Hastalloy) is not required. Plain industry standard commercial off the shelf SiC can be used in the heat exchangers…there is no need for hideously expensive carbon-carbon composites. For the reactor vessel, plain old iron will do the job. Keep the AHR construction materials simple and cheap. This makes the AHR fast to build and therefore cheap to finance.


Once again from Per Peterson’s post:


Quote:
I'm not a materials expert, but I'm pretty sure that Hastelloy N and other austenitic stainless steels have relatively poor performance under neutron irradiation. That is one of the main reasons that the early use of stainless steel cladding was replaced with ziracaloy for LWRs and ferritic steel for SFRs. Ferritic steels are limited in the temperatures they can support (SFR's are limited to temperatures under 510°C for conventional ferritic steel, and under 550°C for ODS ferritic steel, which leaves very little margin for freezing with fluoride salt. Zirconium alloys will corrode severely in fluoride salts.




But Per Perterson still does not go far enough. He still wants to use “clean FilBe” even though that coolant is inferior to pure lithium.


Pure lithium melts at just 180.54 C; no more worry about freezing with fluoride salt!


No fluoride means that Zirconium alloys can do the job nicely in the AHR as follows:


viewtopic.php?p=27624#p27624

Yes Nano-Iron:

Quote:
But the NC State researchers have developed an iron-zirconium alloy that retains its nanocrystalline structures at temperatures above 1,300 degrees Celsius – approaching the melting point of iron.



Lithium is hard on Zirconium but a coating of beryllium or silicon oxide on the Nano-Iron will not only block hydrogen, deuterium, and tritium from escaping the reactor vessel but also protect the Zirconium in the Nano-Iron from corrosion.


These new and exciting possibilities make a second look at the AHR redesign a prudent decision.


More about the Per Peterson’s use of “clean FilBe” even though that coolant is inferior to pure lithium.


Per Peterson has said:

Quote:
On the question of corrosion, it is likely that materials can be developed that will have adequate service life with fuel salts. But thin section components (e.g., intermediate heat exchangers) must be designed to be replacable since they will credibly be the most subject to materials degradation and potential failure. Noble metal fission products tend to precipitate in cold parts of the fuel loop, meaning the IHX's. One must have the capacity to perform periodic in-service inspection to monitor for tube degradation (as one does during outages for PWR steam generators). This in-service inspection may be challenging due to the radiation and after-heat generation levels one would expect in the IHX, so technology development is needed in this area as well.



In the AHR, the heat exchanges can be located inside the reactor vessel. They can be straight SiC tubes. Pure lithium can be the intermediate heat exchange fluid. There is no need to circulate the slurry…that only leads to erosion through abrasion. There is no need to develop new materials. There is no corrosion, no associated service life problems, no replacement strategy needed, no noble metal precipitate in cold parts of the fuel loop because there is no fuel loop.


The heat exchangers can follow the coal boiler model of vertical boiler pipes extracting heat from a (now nuclear) heat source; the fuel slurry will just roll off their smooth vertical sides…very simple… age old… and very robust.


Simplify is the catchword. There is simplicity and elegance to the idea that led Alvin Weinberg to favor the development of the AHR. This simplicity was personified by the saying that it was just “a pot, a pipe, and a pump.”

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PostPosted: Apr 01, 2010 10:30 pm 
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Axil wrote:
The one great advantage that the Aqueous Homogeneous Reactor (AHR) has over the MSR or the Lftr is that the AHR does not use fluoride. It can be rapidly built with currently available low cost tried and true nuclear code approved structural materials. And the AHR can be a true thermal breeder reactor.


No Axil, it is a severe disadvantage. Aqueous reactors have to operate at high pressures, fluoride reactors do not. Fluoride's corrosion problems can and have been solved. The high-pressure problem is fundamental to the aqueous design.


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PostPosted: Apr 02, 2010 12:06 am 
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Some of what I understand from what Axil says is unexcptionable:-

Quote:
Simplify is the catchword. There is simplicity and elegance to the idea that led Alvin Weinberg to favor the development of the AHR. This simplicity was personified by the saying that it was just “a pot, a pipe, and a pump.”

Simplicity of AHR, even with non-homogeniety of solid thorium suggested by me is unparalled. It also retains the advantage of constant removal of volatile fission products Kr and Xe of fluid fuel reactors.

Quote:
The one great advantage that the Aqueous Homogeneous Reactor (AHR) has over the MSR or the Lftr is that the AHR does not use fluoride. It can be rapidly built with currently available low cost tried and true nuclear code approved structural materials. And the AHR can be a true thermal breeder reactor.

AHR is more likely to be a true thermal breeder. Better high pressure reactor vessels can be accepted for bulk of cheap power from thorium if costly heavy water can be avoided. High temperature reactors have their uses (such as burning TRU's) but that can be kept to fast uranium fueled power plants. DOE is looking for disposal of spent fuel (25% cladding, 72% U238).


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PostPosted: Apr 02, 2010 5:15 am 
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Axil, you should read the report of the AEC's Fluid Fuel Reactor Committee, which did not recommend AHR development. ORNL AHR research was shut down shortly after that report was written.

I am not sure where you are coming from with your corrosion claims. The inter- granular cracking problem encountered during the MSRE were not related to Fluoride salts, they were related to dissolved FPs that penetrated the Hastelloy N. The corrosion resistance of Hastelloy N in a Fluoride Salts reactor environment was proven by the MSRE. Subsequent ORNL research pointed to two promising solutions to inter- granular cracking problem.


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PostPosted: Apr 02, 2010 8:44 am 
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Yes, here it is:

http://www.energyfromthorium.com/pdf/TID-8507.pdf

Processing solid thorium oxide is nearly intractable. This is another fundamental disadvantage of the aqueous approach.


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PostPosted: Apr 02, 2010 2:35 pm 
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Charles Barton wrote:
Axil, you should read the report of the AEC's Fluid Fuel Reactor Committee, which did not recommend AHR development. ORNL AHR research was shut down shortly after that report was written.

I am not sure where you are coming from with your corrosion claims. The inter- granular cracking problem encountered during the MSRE were not related to Fluoride salts, they were related to dissolved FPs that penetrated the Hastelloy N. The corrosion resistance of Hastelloy N in a Fluoride Salts reactor environment was proven by the MSRE. Subsequent ORNL research pointed to two promising solutions to inter- granular cracking problem.



Quote:
Axil, you should read the report of the AEC's Fluid Fuel Reactor Committee, which did not recommend AHR development. ORNL AHR research was shut down shortly after that report was written.



I have already posted on this thread the following:


Quote:
In those times long past, The AHR was supplanted by the MSR. In those days, such a decision may have held some merit.


Over these many years since the prototype of the AHR was first tested, many new and exciting technologies have matured and can be repurposed to improve the design of this type of reactor. In my opinion, this accelerating march in technology especially in chemistry can be much more impactful to the AHR design as applied to the pure thorium fuel cycle than anything that can be applied to the MSR.


Many passive safety and fissile breeding features and benefits are advantages that the AHR brings to the table demanding in all prudence a second look.



Ironically as it turned out, the MSR solution recommended in this report was also flawed due to the “graphite plumbing problem”.


Nobody around here likes using graphite very much, but in the context of a fluoride based coolant using graphite is the only way that a thermal breeder can be configured. I want to think about other ways that a thermal breeder can be configured.


Quote:
I am not sure where you are coming from with your corrosion claims.



Per Peterson has posted here “In looking toward future priorities, economics is emerging as a major issue.”


Mitigating corrosion costs money. This is an exercise in tradeoffs. What design tradeoffs can be made to save money; to get to the lowest cost solution? When something works you just want to see if it can be made for less money. This is called value engineering.


The design that is the simplest and the least costly will win the day. The PB-AHTR is very complicated in its attempt to solve the “corrosion expense problem”. The PB-AHTR is full of tradeoffs.

The Lftr does a better job at corrosion mitigation and its design is well formulated but the cost of such mitigation, I think, can be reduced still further in a liquid thorium reactor.

As an example, David L posted as follows:

Quote:
I can`t recall if I mentioned online yet but I heard second hand from Per Peterson at Berkeley that some tests on SiC/SiC composites in fluoride salts at elevated temperatures (800C) did not work out well. The work as done at University of Wisconsin … I wonder what this does for the concept of compact heat exchangers, wasn`t SiC their choice material? That would be bad news if these type heat exchangers couldn`t work for either molten salt fueled (like ours) or molten salt cooled (as Forsberg and Peterson are promoting).



SiC/SiC composites are great materials for heat exchanges. SiC resists tritium penetration tens of thousands of times better than does any metal. Tritium will go right through hot carbon composites.


David L again states “simple carbon composites. For the fusion folks, they don`t like them because gases can
tend to diffuse through.”


I am coming from am open minded examination of possible lower cost alternatives to fluoride salts in a liquid thorium reactor.


To avoid confusion, the reactor concept that I have been describing is not an Aqueous Homogeneous Reactor anymore. It might be called the Lithium Homogeneous Reactor (LHR).


Lithium is great, I think that pure lithium 7 is a great liquid coolant for a thermal reactor, and lithium 6 is a great coolant for a fast spectrum reactor. I don’t understand why sodium is used over lithium 6.


Adding fluorine to Lithium just degrades it coolant capacity and overall performance.

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PostPosted: Apr 02, 2010 3:14 pm 
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If you mean to use liquid Li as your carrier fluid rather than H20 you would reduce confusion if it wasn't in a section titled aqueous.

I'm not much of a chemist but I imagine any hot element from the far left or far right of the periodic table (excluding nobles) will be very reactive and will simply refuse to be elemental - it will combine with something.

Combining lithium and fluorine makes for a very strong ionic bond and these two would rather be with each other than anything else.

The corrosion problem I think you must be referring to is tellerium granular attack. It will take a bit more R&D money to prove the results but ORNL made good progress and seemed confident of a resolution. The Russians and French both seem confident that this can be solved. The solution involves making small changes to the minor constituents of the Hastalloy-N. It represents virtually no production cost - just some R&D expense up front.


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