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PostPosted: Nov 26, 2013 9:54 am 
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If you smash a 1 GeV proton into lead or some other heavy object you get 20-40 neutrons or something like that (not sure the exact figure). This could then go to make say 20 fissions, so you get 20x200 = 4000 MeV, 4 GeV. You get your energy back.

If you smash a 0.2 GeV proton into plutonium and it fissions you get 0.2 GeV back.

Your mileage in case of fission is at best 1:1. If the accellerator is 25% efficient (?) then you need to fission 4 kg of fissile to generate the power to destroy 1 kg of plutonium. EDIT: plus a 50% efficient reactor means its 8 kg of fissile to destroy the additional kg of plutonium.

That's absurd. Real world figures may be worse than this due to target losses etc.

I'm not sure if it fissions actually, more likely it smashes into many neutrons and something terribly radioactive and relatively light like a fission product. Some of the products may be long lived (different than fission products) so you may not achieve anything here.

If you want to smash plutonium-iron then it must be uncladded which means its a nightmare even compared to MSRs. LAMPRE had cladded molten Pu/Fe fuel.

Heavier particles than protons are disproportionally more difficult to accellerate. Even accellerator people admit that its not attractive to use heavier particles.


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PostPosted: Nov 26, 2013 2:49 pm 
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What seems to be lost from this conversation is if you keep the actinides within a neutron flux they will all eventually burn, the trick is to not extract them. (and obviously a faster spectrum does a better/faster job of actinide burning than a thermal one, but even thermal systems will get there eventually)


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PostPosted: Nov 26, 2013 5:07 pm 
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Lindsay wrote:
What seems to be lost from this conversation is if you keep the actinides within a neutron flux they will all eventually burn, the trick is to not extract them. (and obviously a faster spectrum does a better/faster job of actinide burning than a thermal one, but even thermal systems will get there eventually)


This.

If you want to convert all actinides, including those with poor cross sections, the most practical thing to do is incorporate these materials into the blanket of a fission reactor. This is simply the most cost effective way to destroy the waste. You could also denature the wastes in a single fluid reactor but then you have even higher fissile requirements.

Then again...

maybe that isn't the simplest method. You could take a design like Project PACER...dump the waste actinides and salt into an underground reinforced cavity, then drop hydrogen or conventional fission bombs in the cavity. That will get you a hell of a lot of neutron flux in a short burst.


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PostPosted: Nov 27, 2013 4:17 pm 
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Some points I question from the included PDF of Rubbia's talk.

Quote:
The recent Fukujima accident, after the previous warning signs of
Three Miles Island accident, has brought to sudden rest one of the
most advanced and heavily Nuclear Energy exploited countries, creating
a strong movement against a continuation of the Nuclear Power.


Three Mile Island wasn't a warning for a Fukushima type accident, it was the result of incomplete instrumentation and lack of understanding of what was going on in the reactor leading the operators to make the wrong choice. Fukushima could have easily been prevented by TEPCO building a higher sea wall and mounting backup generators on the top of buildings, the company had over a decade of warning about the possibility of very high tsunamis in the past in the region.

And much of the damage from both incidents has been more psychological than physical, maybe that's the lesson we need to take from both.

Quote:
This has proven the inadequacy of the present “probabilistic” concept
vastly used by the Nuclear Community and the necessity of an entirely
new, alternative, “deterministic” approach. In order to be vigorously
continued, Nuclear Power must be profoundly modified.


Why must it be modified, for zero possibility of risk?

What other sector is being held to something even close to this standard. The initial drive in the US and other related countries was to engineer not design the risk out of NPPs with a very high rate of success, we don't read weekly of serious nuclear accidents, they come per decade or less. And revolutionary design was already produced in the 1960s, they're called passively safe Molten Salt Reactors. It seems to me there's far more to go wrong with reactors relying on active particle beam control of criticality than a reactor designed from the start to rely on it's own internal geometry and inherent control measures for stable operation. An accelerator adds another levels of complexity, the whole point of designing MSRs by the people who created nuclear power production in the first place was to make reactors as self stable as possible.

Quote:
New breeding reactions based on Tritium, natural Uranium or Thorium
and which may last for many thousand years, far beyond fossils, must
be pursued but with much stricter safety and deterministic levels. The
long-lived waste problem has to be solved. For such new processes a
distinction between renewable and not renewable energies is academic.


Doesn't this describe LFTRs, producing far less waste and being far more efficient with the input fissile material. FS-MSRs can further be developed to deal with the large stockpiles of spent fuel we already have. It seems to me with the combination of designs like ESBWR, AP1000 and the coming thorium MSRs we've got all the technology to produce safe, ample power we need.

Isn't the idea to take what's already been done and bring it into a modern state of economic and technological development as efficiently as possible. It's crawl, walk, then run, and that should mean getting a functional LFTR certified as soon as possible then worrying about adding complex refinements latter.


Last edited by DougC on Nov 27, 2013 5:27 pm, edited 1 time in total.

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PostPosted: Nov 27, 2013 4:55 pm 
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Mr. Big Nobel Prize Winner Rubbia is painfully poorly informed. The current approach to safety is partially deterministic and partially probabilistic. There are a great many deterministic requirements such as the single failure criterium, TMI requirements, operating procedures and inspection practices, etc. Probabilistic analysis is always needed because no deterministic approach results in zero probability of failure in the real world. Accellerators are active components that can have logic and trip failure, they are basically a different type of control rod with different but very real failure modes.

It's reasonable to state that common sense has failed in the final design of some nuclear powerplants. If you look at how Windscale, Chernobyl, and Fukushima were designed, there are very major design flaws in each of these, to the point of being glaringly obvious mistakes. But a proper probabilistic analysis would have caught the errors easily. One in 50-100 year tsunami (based on simple statistical records) leading to station blackout is way not acceptable in a properly done probabilistic analysis.

There was no control rod failure at any Fukushima unit. So accelletors, basically billion dollar control rods, are an answer in search of a problem. The issue was decay heat, which accellerators magnify due to increased complexity of the core, target material overheating scenarios, etc.

Modern nuclear plants have increased deterministic defences. The best examples being passive core and containment cooling systems which will work without any power. Rubbia's concepts are considerably more dangerous, both deterministically and probabilistically, than something like an ESBWR.


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PostPosted: Nov 27, 2013 5:32 pm 
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I think the predicted failure rate for ESBWRs is three serious reactor incidents per 100,000,000 years that's getting pretty deterministic already isn't it.

It seems to me the only practical method to even get core material out of an ESBWR core in any rational time period is striking the reactor with a nuclear weapon, at which point the reactor contamination is probably the least of your worries.


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PostPosted: Nov 27, 2013 8:04 pm 
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Quote:
Rubbia's concepts are considerably more dangerous, both deterministically and probabilistically, than something like an ESBWR.


What do you think about the decay heat removal system of the Rubbia's Energy Amplifier ?

The reactor is in a double vessel and It uses a passive air cooling to cool the external vessel. If you have holes in the inner and the outer vessel, the leak of the molten lead can clog the air current and you lose the passive cooling. It's also a weakness in the containment. Am I correct ?

It also uses natural convection of the molten lead to transfer the heat of the core to the heat exchangers located at the upper part of the vessel. Maybe it can also use natural circulation in the secondary loop (which I believe is the power generation fluid). But It must have enough lead in order to keep the heat exchangers submerged in lead in case of failure of the two vessels, it's not obvious because the vessel has a great height.

On the other side you have a lot of time to mitigate this kind of accident because you have a lot of lead and you can put water on lead I guess. Maybe you have more than 72 hours to do something, like with the ESBWR.


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PostPosted: Nov 28, 2013 5:59 am 
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You are correct Fab. A dual vessel and containment failure would block passive cooling flow. Hence severe core overheating and failure. This is then aggravated by the RVACS which is open to air. It will act like a chimney to help push out radionuclides, fission products from the failed (overheated) cladding plus some polonium from the coolant. Definately not a safe situation here.

Now if a double failure occurs with an ESBWR for example, then at least you have a huge time for core dryout and boiloff to occur, so you have a lot of time to add water through a variety of ways (spray, pool makeup, direct vessel injection). This time would not be available in the accellerator system. You have a somewhat signficant release of polonium nearly instantly, and a large release of fission products soon after due to the reduced heat capacity of the core (compared to the heat capacity of millions of liters of water than ESBWR has before core uncovery).

Of course Rubbia may rebut this by mentioning it is extremely unlikely for both the vessel and containment vessel to fail, but it isn't impossible (ie beyond design basis earthquake rupturing the seismic isolators and subsequently vessels). Hence the only defence for this design is, ironically, a probabilistic defence.

Deterministically it clearly isn't safe.

In addition to the unlikely RVACS failure postulated above, any system with an accellerator has increased fragilities that do not occur in conventional fission reactors. In particular, things like proton windows that must pass protons but keep out nasty radionuclides, the increased and diverse radionuclides produced from the target material, increased geometrical complexity from the target and -neutron transport to core requirement...

Now, I'm not saying such a reactor is dangerous. It's clearly safer than coal.

But it's clearly not safer than conventional fission reactors.

In my opinion the best design approach is to start with a deterministic design from scratch, then refine it with probabilistic analysis later on. This way we get the best of both worlds, the common sense from deterministic approaches that eliminates certain scenarios altogether (like station blackout), but the refinement and efficiency of the probabilistic approach where determinism would be unreasonable or impractical (some scenarios have no upper bound - eg asteroid strike).


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PostPosted: Nov 28, 2013 6:45 am 
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Well, thanks Cyril.


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PostPosted: Nov 29, 2013 9:32 am 
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E Ireland wrote:
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.



I'm not finding large proton fission cross sections for Pu-242. The proton, fission cross sections typically are not much different than neutron fission cross sections. For example, for Pu-242, up to a couple of hundred MeV the Pu-242 (p,f) cross section is less than 2 barns (again, similar to neutron fission). Perhaps at higher energies protons have an advantage, but I don't have any data handy on that. The other reason why you don't directly use protons is because they are too valuable for producing neutrons. From spallation you get a multiplication of ~20 or so and if you are operating your ADS with a keff of 0.95 you get a multiplication of another factor of 20, for a total of a factor of 400. The proton, fission reaction would have to be 400x as effective as neutron fission to be competitive.

Of course, you can just make keff=1 and forget the whole accelerator thing.


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PostPosted: Nov 29, 2013 11:48 am 
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E Ireland wrote:
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.

Perhaps you could provide a reference. I don't find any.


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PostPosted: Nov 29, 2013 11:55 am 
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Lars wrote:
E Ireland wrote:
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.

Perhaps you could provide a reference. I don't find any.


The evaluation nuclear data files has proton data up to 200 MeV. You can find a summary in:

http://www.oecd-nea.org/janis/book/book-proton.pdf


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PostPosted: Nov 29, 2013 4:02 pm 
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A comparison of fission in various isotopes using neutrons, protons and photons (gammas):


Attachments:
Pb208_Bi209_Th232_U238_Pu239_(n,f)_(p,f)_(g,F)_to_100MeV.gif
Pb208_Bi209_Th232_U238_Pu239_(n,f)_(p,f)_(g,F)_to_100MeV.gif [ 17.82 KiB | Viewed 740 times ]
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PostPosted: Nov 30, 2013 12:24 am 
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FUKUSHIMA,And The End of Humanity.Michio Kaku

https://www.youtube.com/watch?v=STSmFZeE50E&app=desktop

Just when you think it can't get any worse.

You NEED to watch this, folks.

Whoops, I posted this in the wrong place. Sorry.


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PostPosted: Nov 30, 2013 3:50 am 
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Michio Kaku is a total crackhead. I've seen many astronomy documentaries with him "starring". All sorts of nonsense about how we couldn't use nuclear warheads to blast asteroids out of their courses because we would all die of radiation (even though there have been many nuclear bomb test and they have had only limited local effects). No surely its better to just let the asteroid smack into the earth eh Michio? Well no, Michio has a plan, use a solar sail or a little counterweight gravity tug. Completely ineffective for larger asteroids.

Then there's even greater nonsense from this guy about "multiverses" and "parallel universes".

This guy is out there. I mean, MILKY WAY out there.


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