Energy From Thorium Discussion Forum

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PostPosted: May 23, 2017 2:48 pm 
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So gamma irradiation is still a steadily growing means of sterilising materials - be it things like medical instruments or papayas, or spices as is commonly practiced in Europe.

But it is hamstrung by the fact that the two typical isotopes are rather expensive:
Cobalt-60 consumes valuable neutrons to manufacture and is almost entirely manufactured in Ontario, future supplies are limited and at the end of the day every 60g of it manufactured is effectively ~239g of plutonium that is not manufactured.

Caesium-137 has issues with the shear cost of the reprocessing required to produce it, and the difficulty of producing insoluble irradiation elements (apparently there have been some high profile issues with leaking sources in recent decades that have effectively killed it for large scale industrial irradiation).

SO I wondered if anyone had ever tried to use LWR or CANDU fuel elements without processing as gamma sources?
There appears to have been some outline work done but nothing specific and no trial installations operated with actual produce or medical material.
I suppose the main challenge would be providing a lightweight shield around the fuel element that attenuates any neutron flux (to prevent significant activation of the material being irradiated) without cutting out so much of the gamma flux that the entire exercise becomes pointless.

Perhaps some sort of borated plastic tube that the elements can sit in at the core of the irradiator?


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PostPosted: May 28, 2017 10:24 am 
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Interesting idea, Ed.

PWR and even the smaller BWR fuel assemblies are probably much too big for this appliation, making them unwieldy and requiring lots of shielding and handling expenses. The fact that they contain significant amounts of volatiles nuclides as well as plutonium doesn't help, either.

CANDU spent fuel assemblies are probably better, with their smaller size. Still you'd probably want some sort of added containment barrier to avoid handling or ageing related leaks of the fuel tubes that would leak gasses. Maybe can it up in a welded stainless steel can.


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PostPosted: May 30, 2017 8:19 pm 
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E Ireland wrote:
So gamma irradiation is still a steadily growing means of sterilising materials - be it things like medical instruments or papayas, or spices as is commonly practiced in Europe.

Caesium-137 has issues with the shear cost of the reprocessing required to produce it,
Sorry, but this doesn't make much sense to me. Why would it be difficult to reprocess SNF for cesium? It comes out almost first with just plain heat!

Snip the end of the tube, plug it into a collector, and heat. That will drive off Xe and Kr, some Te (IIRC) maybe a few other elements, then cesium. Switch a valve to put the cesium in a seperate pot. Seems simple enough to me.

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PostPosted: May 30, 2017 8:24 pm 
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KitemanSA wrote:
Sorry, but this doesn't make much sense to me. Why would it be difficult to reprocess SNF for cesium? It comes out almost first with just plain heat!

Snip the end of the tube, plug it into a collector, and heat. That will drive off Xe and Kr, some Te (IIRC) maybe a few other elements, then cesium. Switch a valve to put the cesium in a seperate pot. Seems simple enough to me.


Because these operations are going to cost hundreds of dollars per kilogramme of spent fuel.
Tens, or potentially even hundreds of thousands of dollars per kilogram of 137Cs recovered.


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PostPosted: May 30, 2017 8:25 pm 
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E Ireland wrote:
KitemanSA wrote:
Sorry, but this doesn't make much sense to me. Why would it be difficult to reprocess SNF for cesium? It comes out almost first with just plain heat!

Snip the end of the tube, plug it into a collector, and heat. That will drive off Xe and Kr, some Te (IIRC) maybe a few other elements, then cesium. Switch a valve to put the cesium in a seperate pot. Seems simple enough to me.


Because these operations are going to cost hundreds of dollars per kilogramme of spent fuel.
Tens, or potentially even hundreds of thousands of dollars per kilogram of 137Cs recovered.

Why?

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PostPosted: May 30, 2017 8:31 pm 
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KitemanSA wrote:
Why?


Because thats what spent fuel handling operations cost these days.
And cutting the cladding open and then attempting to volatilise the caesium is going to leave you with a lot fuel elements that are going to have to be properly reprocessed or repacked into some other waste form.
This is all going to have to be done in a full blown reprocessing plant style settup with huge radiation shields, no electronics or fibre optics and all that.


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PostPosted: May 31, 2017 1:23 am 
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The used fuel storage should be given a new dimension.
On arrival, the bundles should be crunched to candu fuel sized pellets/billets and clad with thorium. These will have high heat value but be short of melting. They could be put in boilers to produce steam for various uses.
When cooled below steam making temperature, they could be used as radiation sources.
When no longer useful as such, they could be pyro-processed to recover fissile fuel for MSR and other useful components.


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PostPosted: Jun 11, 2017 7:40 pm 
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E Ireland wrote:
KitemanSA wrote:
Why?


Because thats what spent fuel handling operations cost these days.
And cutting the cladding open and then attempting to volatilise the caesium is going to leave you with a lot fuel elements that are going to have to be properly reprocessed or repacked into some other waste form.
Somehow this seems quite excessive. Take an assembly. Remove a rod. Poke a small hole in the end of the rod. Heat till the cesium comes out. Separate the volitile elements (if needed). Reseal the rod. Put it back into the assembly. Repeat thru the assembly. Return assembly. Repeat thru stored assemblies till desired Cs obtained.

From whence comes the extreme cost?

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PostPosted: Jun 12, 2017 3:28 am 
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If the whole fuel bundle is too big to handle, Declad and wet grind the ceramic fuel. Cs and some other highly radioactive parts can be leached out with water or weak acid. The rest could be stored in containers reconstituted from cladding.


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PostPosted: Jun 12, 2017 5:10 am 
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KitemanSA wrote:
Somehow this seems quite excessive. Take an assembly. Remove a rod. Poke a small hole in the end of the rod. Heat till the cesium comes out. Separate the volitile elements (if needed). Reseal the rod. Put it back into the assembly. Repeat thru the assembly. Return assembly. Repeat thru stored assemblies till desired Cs obtained.

From whence comes the extreme cost?

You can't simply "reseal" a rod, otherwise no fuel assemblies would ever need overpacking. It is highly unlikely you could reliably obtain leaktightness sufficient to satisfy regulators once you start cutting into the cladding of a spent fuel assembly.
Nevermind that the rod might not like being heated to 1300C and then cooled again.


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PostPosted: Jun 12, 2017 7:22 pm 
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jagdish wrote:
If the whole fuel bundle is too big to handle, Declad and wet grind the ceramic fuel. Cs and some other highly radioactive parts can be leached out with water or weak acid. The rest could be stored in containers reconstituted from cladding.
What a great way to make it cost a bundle like E Ireland keeps saying.

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