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PostPosted: Nov 24, 2013 5:33 pm 
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Well Kirk, I guess you will have to ask the ADS guys to explain their choices in the next conferences.


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PostPosted: Nov 25, 2013 2:41 pm 
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That' s something I always thought about, granted that most of the MSR troubles are in the upfront costs (fissile start-up, uranium 233 need, etc...), why don' t invest in the idea of a hybrid ADS-MSR, i.e. subcritical fluid fuel reactor powered externally by an accelerator ? This would avoid the need of an high fissile start up, particurally of impratical U-233, of a fast fuel/salt reprocessing/recycling, etc...


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PostPosted: Nov 25, 2013 3:36 pm 
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Alex P wrote:
That' s something I always thought about, granted that most of the MSR troubles are in the upfront costs (fissile start-up, uranium 233 need, etc...), why don' t invest in the idea of a hybrid ADS-MSR, i.e. subcritical fluid fuel reactor powered externally by an accelerator ? This would avoid the need of an high fissile start up, particurally of impratical U-233, of a fast fuel/salt reprocessing/recycling, etc...

As I heard, the thought was to be super-critical then add control rods. In other words, they need even more startup fissile than LFTR proper. I have heard folks talk as if you could make your fissile with the accelerator but this isn't realistic unless you get very dramatic improvements in the accelerator. I think the challenges of getting 233U or doing the processing are far less. And in the meantime we can go the DMSR route and avoid even those challenges in the short term.


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PostPosted: Nov 25, 2013 3:38 pm 
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Electrobreeding isn't practical. You're fighting up against the foothills of e=mc2. Never a good place to be fighting.

Fissile materials produce electricity. Not the other way around.

Asking why not put an accellerator onto a molten salt reactor is like asking, why not strap a jet engine to a car? Well you could and it would work, but at great cost and no gain - in fact there are only negatives, such as increased cost, increased fuel consumption, increased noise, increased emissions... except for a certain techno gee whiz factor. Yes, it's clear that Rubbia is a gee-whiz kind of guy.


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PostPosted: Nov 25, 2013 3:52 pm 
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I think most of the people at CERN are, by default, big fans of accelerators. Convincing them not to attach an accelerator to a reactor is going to be a real challenge. Convincing governments across the Continent that the guys at CERN aren't the smartest people in the world is a real challenge.

Result---continued government funding into the concept of an accelerator-driven reactor. And frustrated reactor guys.


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PostPosted: Nov 25, 2013 5:52 pm 
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I'm a little confused by this, if Weinberg and his people could build a working MSR in 1965, albeit a small one that used active cooling and had no electrical generation then where's the drive to add complexity by things like accelerators for criticality control. From what I've read ORNL was ready in 1973 to begin building the MSBR, which would have cost a fraction of the cost of the LMFBR and could have been online in the mid 1980s.

What is it about the design that some people want to add a bunch of stuff to what appears to me to already be an elegant design. Once you get past the high heat containment and high pressure in the generation loop that Cyril and others have pointed out here.

And wasn't a preliminary form of instream processing already achieved with the MSRE, what are the hurdles that some seem to think need complex solutions to cross?


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PostPosted: Nov 25, 2013 6:15 pm 
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I think it would be difficult for someone who has been president of CERN, as Carlo Rubbia has been, to propose something without an accelerator. At a previous thorium conference, there was also the Project-X proposal from Fermilab, involving a new LINAC coupled to a subcritical reactor. But it appears to me that these physicists are really more interested in funding for new and fancy accelerator technology, advancing the scientific boundaries of particle physics, than in "uncool" and "unsexy" nuclear energy and reactors.

Nevertheless, coupling an accelerator to a subcritical reactor, might make nuclear energy less threatening in the perception of the general public and the politicians, and make them more willing to provide funding for such projects (life is often, and sadly, about perception). The question should also be asked what big physics challenge is next for the particle physics/accelerator guys after the Higgs-Boson has been "discovered" by the LHC. The destruction of "nuclear waste" and the provision of cheap, plentiful nuclear energy by ADS reactors might be that next big challenge that could warrant a lot of public research funding, although ADS reactors are overly complicated in comparison to MSRs.

A couple of months ago there was the ADSMS concept proposed by professor McIntyre of Texas A&M University who wants to "fire" molten chloride salt pots with neutrons from a cyclotron. Some of this research might also be of interest to people who are interested in MSRs.


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PostPosted: Nov 25, 2013 7:25 pm 
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Governments generally make very poor decisions in where to allocate financial resources. We should be more worried about getting private industry to open their pockets to advanced nuclear than to worry about pandering to baseless fears about nuclear criticality to obtain funding to attach a worthless appendage to a perfectly useful reactor. Shame on Rubbia and all the other ADS advocates for their active obfuscation of the progress of clean, safe nuclear energy.


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PostPosted: Nov 25, 2013 8:21 pm 
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Accelerator driven systems can do things that nothing else can though.

Like obliterate annoying isotopes in heavily degraded plutonium by shattering it with masses of protons.

Out of interest, why do all ADS systems that I have seen use a DU or comparable target for the proton beam and then feed the reactor with spallation neutrons from it instead of simply hitting the fuel elements with the proton beam?

It appears even the most dogged nuclear 'ashes' like 242Pu have huge (p,f) and (p, xn) [where x is a relatively large number] cross sections which would lead to them rapidly being incinerated.


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PostPosted: Nov 25, 2013 11:04 pm 
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E Ireland wrote:
It appears even the most dogged nuclear 'ashes' like 242Pu have huge (p,f) and (p, xn) [where x is a relatively large number] cross sections which would lead to them rapidly being incinerated.


Really? I don't even see proton-fission reactions reported out in my nuclide data table.

Code:
    <Nuclide nuclideID="942420" name="242Pu" atomicMass="242.0587368" decayConstant="5.879111E-14">
        <airMPC>1.52E-14</airMPC>
        <waterMPC>7.71E-8</waterMPC>
        <recoverableEnergyMeV>4.982</recoverableEnergyMeV>
        <recoverableEnergyGamma>2.95E-4</recoverableEnergyGamma>
        <DecayFractions alpha="1.0" spontaneousFission="5.49E-6"/>
        <XSNeutronGamma thermal="20.426" resonance="50.376" fast="0.042482"/>
        <XSNeutronFission thermal="0.0010487" resonance="0.15445" fast="1.4034"/>
        <XSNeutron2Neutron fast="0.010156"/>
        <XSNeutron3Neutron fast="6.4464E-5"/>
    </Nuclide>


Not that 242Pu keeps me up at night, wishing for an accelerator. I'm a lot more concerned about 239Pu, which a critical fission reactor will take care of nicely.


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PostPosted: Nov 25, 2013 11:05 pm 
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Destroying isotopes with an accelerator will be done on a scale of grams per year. Using fission will be literally a thousand times more productive.


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PostPosted: Nov 26, 2013 12:13 am 
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It has become very quickly clear that being at CERN and even worse getting a Nobel prize very quickly goes to your head. Both Carlo Rubbia and Jean-Pierre Revol were very condescending to others reactor types at the conference and even rude to their own accelerator colleagues. Rubbia was highly offended that someone would dare to question whether he had done an economic analysis to demonstrate the benefits of his ADS system, yet later the same day Carlo grilled another ADS proponent on why they had not done an economic analysis and ridiculed them saying their system wouldn't work for that reason. He has lost the ability to interact socially and professionally with other scientists. Don't get me wrong, he is still brilliant, but has lost the ability to be profesionally self sceptical. Jean-Pierre is not as bad, but also is not able to be self-sceptical and does not entertain the thought of being wrong.

I did expect that the conference would have a heavy load of with ADS systems at CERN, but not to the 50% extent and not to get ADS systems to basically be made one of two of the International Thorium Energy Organization's platforms. Second tier platform at best.

However, accelerators as neutron or charged partical materials irradiation testing devices, as medical radio-isotope producers, as neutron gamma spectrocopy for isotopic and elemental analysis of materials, etc. are still perfectly viable uses of accelerators. Increased power and reliability devices are even needed for these purposes because accelerator trips can cause cycles thermal temperatures during irradiation which is a different type of stress to the material and cloud the results of the irradiation results. It is also known that irradiation at lower temperatures following a cooldown is generally worse for brittle fracture performance because they damage tends to stay, rather than being annealed out. And, of course higher power means faster irradiation test results, and more test campaigns completed for more through put.


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PostPosted: Nov 26, 2013 4:52 am 
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Kirk Sorensen wrote:
E Ireland wrote:
It appears even the most dogged nuclear 'ashes' like 242Pu have huge (p,f) and (p, xn) [where x is a relatively large number] cross sections which would lead to them rapidly being incinerated.


Really? I don't even see proton-fission reactions reported out in my nuclide data table.


The figures I see suggest total proton induced reaction cross sections of at least several hundred barns (almost totally fission), which when you are dealing with a long lived isotope with a negligible fission cross section and a ~20b capture cross section, is huge.

Kirk Sorensen wrote:
Not that 242Pu keeps me up at night, wishing for an accelerator. I'm a lot more concerned about 239Pu, which a critical fission reactor will take care of nicely.


Why would you be concerned about 239Pu?
It is relatively non radiotoxic and fissions very easily.

242Pu gets in the way and doesnt fission or go away any time soon, it is essentially 'ash'.


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PostPosted: Nov 26, 2013 7:52 am 
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Proton fission is exactly what you don't want. The (p, xn) reaction for say a 1 GeV proton has a very big "x" number, whereas fission would produce far fewer neutrons.

Regarding shooting protons into the fuel itself: that is inefficient. Solid fuel has cladding which is mighty blocking the protons. Even liquid fluoride fuel has mostly F, Be, Li, that attenuate protons without high neutron yield. It's a waste of costly high energy protons.

Like Lars said, accellerator conversion of actinides is very poor compared to fission. Imagine taking the exhaust from your car and trying to convert that back to gasoline with electricity from the generator from the engine which has combusted the gasoline... this gets pretty stupid pretty fast for any meangingful amounts of gasoline, and most would argue that putting all that electrolysis, synfuel equipment and oversized generator in the car is needlesly costly and complicated even with zero gasoline production in the first place.

The basic advent of fission is that you can convert a small amount of mass into a large amount of energy. Sticking an accellerator onto it turns that advantage into a disadvantage: it is trying to turn a large amount of electricity into a small amount of mass conversion, even with all the neutron leverage it still makes no sense.


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PostPosted: Nov 26, 2013 9:04 am 
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I don't want the neutrons, I want the target isotope obliterated, neutrons produced by fission and spallation are merely a bonus.

And if you are shooting at Plutonium you could always take a leaf out of the book of the LAMPRE and go for a Plutonium-Iron eutectic which is 90.5 atom percent Plutonium.

You probably wouldn't use protons with anywhere near a GeV either, a couple hundred MeV would easily be sufficient, the extra energy would be better fed into increasing the driver current instead.

If you use Alpha particles it appears energies as low as ~50MeV are sufficient to trigger large scale 242Pu fission.


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