Energy From Thorium Discussion Forum

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PostPosted: Mar 24, 2014 1:25 am 
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As I understand, nuclear reactors need a very small of neutron producing material to initiate the reaction and achieve criticality.


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PostPosted: Mar 24, 2014 5:41 am 
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In theory - in practice you can just very slowly ease the reactor through the theoretical criticality boundary until a reaction starts from a uranium spotantaneous fission.

This is not the preferred mechanism in the west, but it is how the first reactors were started.


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PostPosted: Mar 25, 2014 1:22 am 
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fab wrote:
Speaking of that, we know that it's possible to use natural uranium in solid fuel, moderated by graphite, and cooled by CO2. So I was curious to know the neutronic possibilities of an MSR moderated by graphite.
Is it possible to achieve criticality with natural uranium (no thorium) in a Flibe's based salt (or in 7LiF based salt) and moderated by graphite ?
I guess that if it's possible the burn-up will be poor without aggressive online reprocessing and refuelling but it's just for curiosity.

A newbie starting with nuclear power and starting an MSR power program are two very different problems. An MSR fuel is a chemical broth and reprocessing of used nuclear fuel has to be assumed.
If thorium fuel or breeder is not the aim, there could be easier solutions.
The simplest starting point is a water tube boiler. The fuel space can be filled with the nuclear fuel in the shape of molten salts. Pressurized water in the water tubes will double as moderator too. The salt could be NaF-ZrF4 as used in the ARE. The nuclear fuel will not require air as in the normal boiler as the nuclear fire will be sustained by moderated neutrons, constantly bred in a critical core. It will be an under-moderated reactor though the moderation can be adjusted to some extent. A substantial amount of uranium from used nuclear fuel can be burnt in such MSR's with fissiles extracted from the same used fuel.
Burning of Thorium in such reactors may require chloride salts with enriched Cl-37.


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PostPosted: Mar 25, 2014 6:46 pm 
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jagdish wrote:
A newbie starting with nuclear power and starting an MSR power program are two very different problems. An MSR fuel is a chemical broth and reprocessing of used nuclear fuel has to be assumed.
If thorium fuel or breeder is not the aim, there could be easier solutions.


My premise is that a nation-state has access to ample but diminishing fossil fuels. They desire to get nuclear power quickly but do not want to have to deal with burying piles of nuclear waste. Reprocessing is assumed, MSRs are an option to have both power and reprocessing of fuel. A solid fuel reactor does seem to be a way to get to nuclear power quickly but developing MSRs shortly after to deal with the solid fuel waste does seem to be a nearly obvious choice.

A nation-state with access to the sea will have an effectively unlimited supply of uranium. Access to cheaper uranium ores and/or thorium will depend on local geography. I think it is safe to assume that thorium and uranium is available in any nation-state that has the infrastructure to manufacture nuclear reactors. While thorium and uranium is essentially available everywhere on Earth that is habitable it's just a matter of how much it will cost. Such a nation-state may find itself in a catch-22, cheap energy means cheap thorium but getting cheap thorium means getting cheap energy.

Thorium fuel or breeder reactors are not the aim, cheap and reliable energy is the aim. The assumption is that nuclear power will bring cheap and reliable energy, it may not be a correct assumption but that is what we are working with. If this assumption is not correct then the thread ends here since further discussion is outside the scope of this forum.

I was just reading news on how Brazil may have to ration power since the drought is threatening hydroelectric production and the rate of power consumption is growing faster than oil fired power plant construction. Brazil is another example of a nation-state that might fit within my premise. They will want more electric production capacity, they have access to uranium from the sea, perhaps thorium rich sands, and lots of oil but perhaps not enough oil production to meet future demands. Access to fresh water may be an issue, power for desalination may be a goal as well. Hydroelectric power means the possibility of storing excess nuclear capacity by pumping water behind the dam.

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PostPosted: Mar 25, 2014 9:57 pm 
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Kurt Sellner wrote:
My premise is that a nation-state has access to ample but diminishing fossil fuels. They desire to get nuclear power quickly but do not want to have to deal with burying piles of nuclear waste.


You just described the United Arab Emirates.

Kurt Sellner wrote:
Reprocessing is assumed,


Except for that part. They had to give up that right to get their Section 123 agreement with the United States.

Saudi Arabia appears to be trying to learn from that mistake by getting their nuclear technology from the Chinese or Russians and avoiding a Section 123 agreement with the US.

By telling countries they can't enrich or reprocess, we send them right to countries that will sell them both technologies. Good move America. \sarc


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PostPosted: Mar 25, 2014 10:45 pm 
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Kirk Sorensen wrote:
Kurt Sellner wrote:
My premise is that a nation-state has access to ample but diminishing fossil fuels. They desire to get nuclear power quickly but do not want to have to deal with burying piles of nuclear waste.


You just described the United Arab Emirates.


Yes. Yes, I did. I also described a lot of other nation-states. I had a lot of places in mind when I created my "rules". What's been on my mind recently is Brazil.

Kirk Sorensen wrote:
Kurt Sellner wrote:
Reprocessing is assumed,


Except for that part. They had to give up that right to get their Section 123 agreement with the United States.

Saudi Arabia appears to be trying to learn from that mistake by getting their nuclear technology from the Chinese or Russians and avoiding a Section 123 agreement with the US.

By telling countries they can't enrich or reprocess, we send them right to countries that will sell them both technologies. Good move America. \sarc


I've seen the mention of "123" before but wasn't quite sure what it meant. Now I know a bit more to look that up, thank you sir.

Is using a modern MSR considered "reprocessing"? Most of what allows more complete burn up of the fuel is that a liquid fuel allows many fission poisons to boil off. Just allowing the xenon to escape has to be quite an advantage.

I suspect that China will be the first to have a utility scale MSR. Once that happens I suspect the federal government in the USA will change its rules and let people research them here. History tells me that a lot of technological advancement happens once someone proves something is possible.

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PostPosted: Mar 26, 2014 1:04 am 
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Currently, it is S.Korea straining at the leads in the 123 matters. Much smaller N.Korea has simply opted out of the control treaty and gone for weapons.
No one has yet introduced MSR for power or for burning the used LWR/PHWR fuel. China could well be the first. S.Koreans may have given them a run for their money if not shackled by NPT/123 agreement.


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PostPosted: Mar 26, 2014 2:13 pm 
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Dumb question, and sorry if it has been answered here, but can a MSR start up on NU?

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PostPosted: Mar 26, 2014 3:13 pm 
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I think that a MSR cannot run on NU, the typical materials (Li7, Be, graphite, Fluorine) capture enough neutrons to prevent the chain reaction. And many other materials have the same issue with NU in a thermal spectrum except deuterium. You may be able to add reactor grade plutonium to the fuel salt and achieve criticality.


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PostPosted: Mar 26, 2014 3:24 pm 
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KitemanSA wrote:
Dumb question, and sorry if it has been answered here, but can a MSR start up on NU?


I did this calculation about seven years ago. Yes, but only with D2O moderation. It's not possible with graphite.


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PostPosted: Mar 26, 2014 5:51 pm 
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Jaro has plenty of suggestions along this line - search for heavy water MSR.


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PostPosted: Mar 26, 2014 11:08 pm 
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Kirk Sorensen wrote:
KitemanSA wrote:
Dumb question, and sorry if it has been answered here, but can a MSR start up on NU?


I did this calculation about seven years ago. Yes, but only with D2O moderation. It's not possible with graphite.
How about the ZrD2?

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PostPosted: Mar 27, 2014 8:35 am 
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Too much absorption from the zirconium.


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PostPosted: Mar 27, 2014 11:33 am 
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You may stand a chance with Beryllium oxide or carbide instead of graphite, if you can keep it solid. I do not claim to be an expert and am open to correction.


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PostPosted: Mar 27, 2014 12:33 pm 
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Kirk Sorensen wrote:
KitemanSA wrote:
Dumb question, and sorry if it has been answered here, but can a MSR start up on NU?


I did this calculation about seven years ago. Yes, but only with D2O moderation. It's not possible with graphite.


When I first saw that I thought, "OK, problem solved." Now that I thought about it more that sounds like an engineering nightmare. What kind of pressures would you need to keep the D2O from boiling away? Even if you can keep your moderator from boiling I suspect that the D2O is hot enough and pounded with enough radiation that it's going to decompose.

I also realized that my premise is flawed in that just because a nation-state does not develop the capability to enrich uranium or plutonium does not mean they will not have the capability to produce weapon grade material. The reactor and reprocessing would have to operate in a manner to prevent weapon grade material from being produced.

For example this heavy water moderated MSR fueled with natural uranium. If there is continuous reprocessing of the fuel then it would be nearly trivial to allow the Pu-239 to accumulate somewhere. They'd have to make sure the plutonium stayed in the reactor long enough for the plutonium to get contaminated with even numbered isotopes. Or do I have this wrong?

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