Energy From Thorium Discussion Forum

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PostPosted: Jan 01, 2013 1:16 am 
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Muons and ADNA proposing using accelerator-driven subcritical reactor for heat for production of synthetic fuels and chemicals

I have posted all the aspects of this concept many times in the past but some parts may have been deleted.

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PostPosted: Jan 01, 2013 7:29 am 
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Interesting, but why should you use an accelerator system in combination with a molten salt reactor ? It looks "cool", but it seems rather pointless to me.


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PostPosted: Jan 01, 2013 11:13 pm 
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It is quite understandable that you want a non-carbon source of heat.
There are decaying isotopes that produce heat. Pu-238 might be in short supply but Sr-90 and Cs-138 can be leached out of used fuel as chlorides. Some level of heat is produced by used nuclear fuel in storage itself.
There are more than 400 reactors producing heat for power. Some could be built and/or operated for process heat.
Why bother for more complicated/costly/unsafe processes.


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PostPosted: Jan 02, 2013 9:29 am 
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GEM-STAR wants to run on TRUs without having to use HEU to make up for expected neutron deficiencies. As the final resting place for such material, it is either a fast reactor or an ADS like GEM-STAR. I'm not sure, but I think Jagdish would prefer a fast reactor. :mrgreen:

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PostPosted: Jan 02, 2013 9:51 am 
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Short version. Accellerators are functionally pointless PR gadgets.

Long version. Accellerators keep the core below criticality when turned off, but there has never been a major control rod failure in any LWR (Fukushima units all shutdown fine with control rods). In fact, to keep the accellerator cost and energy drain acceptable, the criticality will have to be kept close to 1, basically over 0.99 in any practical design (and it's still not practical to deal with high energy protons in an environment that is already burdened enough with high energy neutrons). Because criticality varies with burnup, the criticality of such a design will at times equal 1 or more, and therefore will need control rods, defeating the very purpose (dubious as it was already) the accellerator tries to achieve!

In addition, it is possible that the accellerator logic fails to trip/scram the reactor when needed, just as a control rod based system can fail. In fact logic failure is much more likely that actual insertion failure, as there are many control rod drivers and the insertion system is robust (often having backup diverse systems such as liquid poison insertion). The idea of earthquake induced instant core deformation blocking control rods is clearly nonsense, as proven by Fukushima.

LWRs and MSRs can also easily achieve negative void coefficients, which is inherent safety (an accellerator control logic is still an engineered system and a complicated one at that).

Someone on this forum compared accelletors strapped to nuclear reactors to strapping a jet engine to a car. Yes, it's technically possible, but serves no purpose. Jet engine powered cars are not safer and not more fuel efficient - quite the contrary is true.


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PostPosted: Jan 02, 2013 12:13 pm 
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I believe I read that they want to run under .95 criticality but I don't recall where.

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PostPosted: Jan 02, 2013 4:57 pm 
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KitemanSA wrote:
I believe I read that they want to run under .95 criticality but I don't recall where.


That's the regulatory limit for criticality. But you can't conform to that in any practical accellerator design; the accellerator would be too big, costly, and energy hungry to make this practical and economic.


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PostPosted: Jan 03, 2013 2:33 pm 
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Cyril R wrote:
Short version. Accellerators are functionally pointless PR gadgets.

Someone on this forum compared accelletors strapped to nuclear reactors to strapping a jet engine to a car. Yes, it's technically possible, but serves no purpose. Jet engine powered cars are not safer and not more fuel efficient - quite the contrary is true.


More like bolting a car engine onto a jet plane.


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PostPosted: Jan 03, 2013 3:32 pm 
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To consume SNF you need a fast reactor structure. The accelerator is an artifact to keep the criticality below 1. Perhaps this simplifies the stability problems of fast reactors. This leads me to a few questions.

Has anyone done a cost projection and energy ballance on the accelerator that will deliver several kg of protons per year at several MEV? That will answer a lot of questions. The project is larger than simply theoretical neutron economy.

Won't the accelerator deliver local hot spots in the fuel since the beam is not widely and uniformly distributed?
Is the neutron mean free path long enough to smooth the locally high neutron flux?

Won't the local flux of secondary neutrons tend to be easily lost from the core since they are created on the surface of the core rather than at the center of the core? Would this lead to poor neutron economy if true.

What do you use as a beam window to shield the beam line from the gasses created in the core? Is the window the source of secondary relativistic neutrons?

A few enginnering details.
Rob

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PostPosted: Jan 03, 2013 6:52 pm 
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Look up GEM-STAR. They have a goodly number of presentations and reports available. Go to the source.

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