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PostPosted: Dec 09, 2008 12:43 am 
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If you can extract 236U for a reasonable price all manner of nice things happen. We skip the 237 node that is so bad for the neutron economy, we skip making TRU's, the U236 is benign and can simply be sent to LLW. In equilibrium I see 550kg of U236 out of 7,700 kg of U. Any idea how accurately we will be able to extract the U236. In particular, we must not include any 233U or 234U into the waste stream, we would prefer to leave the 235U in the reactor but we can afford some leakage of 235U into the waste stream. How much of the u236 can we hope to pull out and at what cost?


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PostPosted: Dec 09, 2008 1:10 am 
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I thought that Np237 is actually valuable, as it can be used to produce Pu238 for RTGs, no?

Or would it be better to extract U236 and than transmute it to Pu238?


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PostPosted: Dec 09, 2008 1:32 am 
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Yes it is valuable but the market is small.

"Since 1993, the U.S. has purchased all of the plutonium-238 it has used in space probes from Russia. 16.5 kilograms total have been purchased." per wikipedia.


At equilibrium a 1GWe reactor has an inventory of 155kg of 238Pu.


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PostPosted: Dec 09, 2008 1:35 am 
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Lars wrote:
If you can extract 236U for a reasonable price all manner of nice things happen. We skip the 237 node that is so bad for the neutron economy, we skip making TRU's, the U236 is benign and can simply be sent to LLW. In equilibrium I see 550kg of U236 out of 7,700 kg of U. Any idea how accurately we will be able to extract the U236. In particular, we must not include any 233U or 234U into the waste stream, we would prefer to leave the 235U in the reactor but we can afford some leakage of 235U into the waste stream. How much of the u236 can we hope to pull out and at what cost?



http://www.fas.org/sgp/othergov/doe/lan ... /silex.pdf

Summary

Do to Laser power factor limitations at the time(2005), Silex “was not capable of producing significant amounts of HEU (highly enriched uranium),” wrote John L. Lyman, who visited Silex Systems with three IAEA representatives in February 2005, when he was working at Los Alamos. He cited a number of important processing limitations.

Limited wavelength- conversion output

One problem is the limited optical output available on the 16 µm line, generated by Raman shifting 10.8 µm output from a pulsed carbon dioxide (CO2) laser in a high-pressure parahydrogen cell. The CO2 lasers can generate 1 J pulses, but only at a limited repetition rate, and only a fraction of the pulse is in the pump band.

Unspecified “additional nonlinear optical tricks” are needed to convert the CO2 pump light to the correct wavelength to pump the Raman cell. The lasers are 1% efficient and the Raman conversion 25% efficient, so the overall efficiency is 0.25%.

Operation of the CO2 lasers at their current 50 Hz repetition rate is not sufficient to produce significant enrichment, according to Lyman. “A mature facility would have the capability to increase that rate by more than an order of magnitude,” he wrote. The problem is not just that higher repetition rates are needed to increase the amount of uranium enriched. “At low rates, the process does not work because of large amounts of unprocessed material in the product stream,” Lyman wrote. “At 50 Hz, only 1% of the material in the feed stream is processed, with 99% going unprocessed, limiting the possible amount of enrichment.”

Another issue is the limited amount of material that can be processed at once. The vapor must be cooled to ensure good separation of the absorption lines of the two isotopes. But under those conditions, Lyman wrote, “rapid catastrophic condensation occurs if the UF6 molecular density gets too high.” In his experience, that maximum density is 10e15 molecules per cubic centimeter.

With many details classified or proprietary, it is hard to quantify the processing. Lyman wrote that if a laser could illuminate a one-liter volume at an ideal repetition rate, it would take about 100 hours to produce one kilogram of U-235-assuming complete separation of the U-235 and U-238 isotopes. However, most processes require multiple stages of separation, and according to Lyman’s comments, a 5000 Hz laser would be needed to process all the feed stream (a mixture of UF6 and an unidentified diluting gas).


Comment:

The key to this technology is a high duty factor laser.

But why not a number of lasers firing like a Gatling gun.

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PostPosted: Dec 09, 2008 8:06 am 
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You guys work all night. Here's a GE description. Is it worth trying to engage companies like GE in the LFTR forum?
http://www.silex.com.au/s03_about_silex/s30_1_content.html


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PostPosted: Dec 09, 2008 10:19 am 
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ref.
http://www.fas.org/sgp/othergov/doe/lan ... /silex.pdf

Quote:
... electrical requirement of 100 Kw for the Laser for a single process vessel. This would be the minim power requirement to process 1.0 kg of U235 in eight days...


If you assume a cost of 6.16 per kilowatt hour( average industrial cost
http://www.eia.doe.gov/cneaf/electricit ... ig7p7.html )

then the cost in electricity is 1182.00 per kilogram of U236( targeted isotope) plus the other costs of the plant. How much value is added to the fuel salt by removal of the U236? Can we put a number on it?


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PostPosted: Dec 09, 2008 3:29 pm 
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Free electron lasers sound perfect. They are efficient, and widely tunable.
The only issue is the radiation hazard from the synchrotron, but this is a
nuke facility, right? No problem. (I was surprised they weren't in use.)

http://en.wikipedia.org/wiki/Free_electron_laser


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PostPosted: Dec 09, 2008 3:55 pm 
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Resource:

https://www.llnl.gov/str/Hargrove.html


There is more then one way to separate out u236. I ran across and enlightening article about the US effort to enrich U235. It seems to me that the government is either grossly incompetent or that there exists a industry conspiracy to undermine nuclear power in the country.

The commercialization of the successful and proven laser isotope separation (LIS) technology was abruptly hated as follows:

However, the tests were interrupted by USEC's decision in June 1999 to halt development of LIS technology because a combination of near-term factors limited its funds. These factors included market-driven price declines for enriched uranium, significant cost increases to operate U.S. gaseous diffusion plants, and the need to continue shareholder dividends. USEC also judged expected investment returns were insufficient to outweigh the usual anticipated risk of new technology.
The decision halted the efforts of more than 500 people, including some 300 Livermore employees. In making the announcement, USEC President and Chief Executive Officer William Timbers, Jr., said, "The Lawrence Livermore team has displayed outstanding dedication, creativity, and responsiveness in its efforts to develop and commercialize AVLIS."



Image

Image

Image


For further information contact Steven Hargrove (925) 422-6178 (hargrove2@llnl.gov).


Steven Hargrove would be a great addition to the forum

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PostPosted: Dec 09, 2008 5:23 pm 
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I think they picked the wrong technology: AVLIS is a lot tougher than MVLIS, IMO.
Silex is of course MVLIS....


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PostPosted: Dec 09, 2008 6:21 pm 
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Equilibrium uranium isotropic composition for a 1 GWe fast reactor is: 4700kg 233U, 1750kg 234U, 555kg 235U, 549kg 236U, (and 0.4kg 237U and 1.3kg 238U). We generate 20kg additional 236U per year (1000kg 233U) * (0.1 absorb in u233) * (0.2 absorb in 235U) = 20kg.

If we process the entire fuel volume in one year we need to process 2.3 liters/hour = (20m^3)(1000 liters/m^3)/365 days / 24 hours. This would reduce our TRU content 25x but won’t eliminate it. So we still would need to do back end TRU recovery.

Any 233U or 234U that leaks into the waste flow is similar to TRU wastes. To get performance similar to 0.4% TRU leakage (with a 10 year cycle) we have to do leak less than 260grams/GWe-yr. So we would need to isotropically isolate the 236U to contain less than 1% 234U+233U. The 235U we would prefer to leave in the fuel but leaking some of it to waste isn’t a major issue. We lose one neutron for each atom of 235U shipped to waste but I would guess we will still win neutronically if we extract the 236U.

The most aggressive TRU processing claimed 4e-6 leakage, to match this performance one would need 0.001% leakage.

So, I think the requirements on U236 extraction is pretty severe - someplace between 1% and 0.001% leakage and processing 2.3 liters per hour. The leakage rate probably means multiple passes through – lets call it 8 passes with no justification. The current processing of 1 liter per 100 hour for a single pass for 100kg. So crudely we would need to scale up the processing about 50x = (2.3l/hr)/(1l/100hr)(20kg/100kg) .

Is there a chance this technology can do this? It seems much harder than the U enrinchment process that is their main target.


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PostPosted: Dec 09, 2008 7:03 pm 
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jaro wrote:
I think they picked the wrong technology: AVLIS is a lot tougher than MVLIS, IMO.
Silex is of course MVLIS....


IMHO, Lawrence Livermore lab picked the wrong country or at least the wrong government. It is not a coincidence that MVLIS comes from an Australian company. Like the IFR, proliferation fears makes the US decision makers irrational in the same way that some environmentalists are dead set and beyond reasoning against nuclear power.

Today, MVLIS is allowed in the US because MVLIS is more resistant to proliferation. Only a small amount of U235 enrichment is possible in the material flow because of intentionally low laser performance.

AVLIS, on the other hand, produces pure isotope. For U235, that is dangerous because of both proliferation and criticality danger.

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PostPosted: Dec 09, 2008 7:43 pm 
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My current opinion is that AVLIS can be a better fit for the Lftr because of the reasons as follows:

Economy

The lasers of MVLIS consume vast amounts of electric power. The lasers of AVLIS are solid state and have a large duty cycle advantage.

The Raman cell is big and not that efficient as compared to dye. It has a relatively low duty cycle as compared to dye.

For MVLIS , the UF6 must be lowered in temperature from 1000C to 80K to be processed.

For AVLIS, the UF6 must be raised in temperature from 1000C to 3000C by electron beam heating which does not use much power at all.


Purity

At 3000C, the fluorine atoms and U236 atoms will dissociate so that the U236 atoms will polarize and be collated on an anode. This disposition will be pure U236. Criticality or proliferation will not be a problem when isolating U236.

The vacuum chamber of the AVLIS can be coated with diamond to eliminate uranium corrosion and increase the MTBF of the vacuum chamber.

The AVLIS technology was proven back in 2000. SILEX is still being developed.

I am not yet an expert on this stuff but will continue to research this. To cut waste to less the dirt levels is worth looking into.

Any advice, knowledge or opinion is greatly appreciated.

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Last edited by Axil on Dec 09, 2008 7:44 pm, edited 1 time in total.

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PostPosted: Dec 09, 2008 7:44 pm 
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Axil wrote:
MVLIS is more resistant to proliferation. Only a small amount of U235 enrichment is possible in the material flow because of intentionally low laser performance.

Are you sure ? ....that's news to me !

AFAIK, the only difference, laser-wise, is the different frequency required to ionise molecules (MVLIS) versus U atoms (AVLIS).

Why should separation performance not be equally good ?

In fact, SILEX was originally planning on marketing its enrichment services to those requiring isotopically pure non-radioactive substances (such as certain Zr isotopes -- they cited a number of other examples).
In each case, the separation was 100% on a single pass, thanks to laser frequency tuning.
Don't see why it should be any different for U, Pu, etc.


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PostPosted: Dec 09, 2008 7:57 pm 
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jaro wrote:
Axil wrote:
MVLIS is more resistant to proliferation. Only a small amount of U235 enrichment is possible in the material flow because of intentionally low laser performance.

Are you sure ? ....that's news to me !

AFAIK, the only difference, laser-wise, is the different frequency required to ionise molecules (MVLIS) versus U atoms (AVLIS).

Why should separation performance not be equally good ?

In fact, SILEX was originally planning on marketing its enrichment services to those requiring isotopically pure non-radioactive substances (such as certain Zr isotopes -- they cited a number of other examples).
In each case, the separation was 100% on a single pass, thanks to laser frequency tuning.
Don't see why it should be any different for U, Pu, etc.


From my pervious post as follows:

Operation of the CO2 lasers at their current 50 Hz repetition rate is not sufficient to produce significant enrichment, according to Lyman. “A mature facility would have the capability to increase that rate by more than an order of magnitude,” he wrote. The problem is not just that higher repetition rates are needed to increase the amount of uranium enriched. “At low rates, the process does not work because of large amounts of unprocessed material in the product stream,” Lyman wrote. “At 50 Hz, only 1% of the material in the feed stream is processed, with 99% going unprocessed, limiting the possible amount of enrichment.”


The laser flickers on and off. When it is off the material flow is not enriched. The duty cycle on these big powerful lasers are low.

For AVLIS, the laser is solid state with a very high duty cycle. When the laser is off, no excited U236 is produced and none is pulled to the anode, but that does not matter because the anode is not in the material stream.


Maybe SILEX degraded the process to meet US government proliferation and criticality requirements.

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PostPosted: Dec 09, 2008 9:33 pm 
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Axil wrote:

IMHO, Lawrence Livermore lab picked the wrong country or at least the wrong government. It is not a coincidence that MVLIS comes from an Australian company. Like the IFR, proliferation fears makes the US decision makers irrational in the same way that some environmentalists are dead set and beyond reasoning against nuclear power.

Today, MVLIS is allowed in the US because MVLIS is more resistant to proliferation. Only a small amount of U235 enrichment is possible in the material flow because of intentionally low laser performance.

AVLIS, on the other hand, produces pure isotope. For U235, that is dangerous because of both proliferation and criticality danger.


First, Hargrove is no longer at LLNL. Hargrove had proposals in to use AVLIS to mine the tails from the GDPs; a clear winner. Next, mix in the politics of zero congressional support for LLNL versus the other districts that would benefit from other enrichment approaches (advanced centrifuges) or the status-quo. The last uranium runs at AVLIS were pretty impressive. There were some material issues that needed to be resolved for sustained performance.


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