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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 14, 2014 9:44 am 
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FLUOREX is indeed very interesting.

But it is very likely dry storage for a century or two would reduce costs to a significant extent as radiation doses from the fuel elements will drop by several orders of magnitude. Requiring considerably thinner shielding.
You might even be able to get away with just glove boxes.


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 15, 2014 7:08 pm 
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E Ireland wrote:
FLUOREX is indeed very interesting.

But it is very likely dry storage for a century or two would reduce costs to a significant extent as radiation doses from the fuel elements will drop by several orders of magnitude. Requiring considerably thinner shielding.
You might even be able to get away with just glove boxes.

Why would you have a person anywhere near this at all?


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 15, 2014 8:31 pm 
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A lights out reprocessing plant is a nice idea.

But unfortunately it is not particularly practical.
Reprocessing plants have hundreds of staff, maintenance of equipment, maintenance of the equipment used to remotely perform the first set of maintenance, loading dock staff, machine operators, the list goes on.


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 16, 2014 2:37 am 
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Reprocessing is skilled work involving chemistry and nuclear safety in handling highly radioactive materials. It changes quantitatively but not really qualitatively with time. Koreans are game to handle the work. The US and IAEA do not seem to be willing to let them handle it like Japan handles it.


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 16, 2014 6:21 pm 
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E Ireland wrote:
A lights out reprocessing plant is a nice idea.

But unfortunately it is not particularly practical.
Reprocessing plants have hundreds of staff, maintenance of equipment, maintenance of the equipment used to remotely perform the first set of maintenance, loading dock staff, machine operators, the list goes on.

Maintenance, loading dock staff, and machine operators - I don't picture any of these guys using a glove box. I picture glove box being used by someone doing small scale experimental stuff.

Moving a fuel assembly would require a machine simply from its weight. It would seem like this could be automated.

It is practical to build a semiconductor manufacturing plant to be fully automated. Why is it not practical to do so for a reprocessing plant. I understand it is not currently done but then the nuclear industry is extremely slow to change due to risk aversion (to the point of adding risk IMHO). Except that it isn't done now, why can't reprocessing be made fully automated?


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 17, 2014 8:20 am 
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They all have to be shielded from the absurdly radioactive materials they are handling.
A glove box is insufficient to shield the room it is in from the radioactive material.

You have to build giant hot cells to protect the building staff, even if they aren't even doing any operations on the fuel itself.
Someone delivering something to the operator will pick up significant doses, especially if t hey are doing that all day long.

Semiconductor fabs are rather different environments, for instance they don't operate in massive radiation fields which will cause bits to flip randomly in SCADA and other equipment, potentially causing machines to freeze up or worse do something unsafe.

All the interlocks on equipment have to be electromechanical rather than the far cheaper silicon based ones used in other fields.


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 18, 2014 8:58 am 
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I can see where that restricts some choices in design of the equipment. All computing needs to be located on the other side of shielding for example. But we deal with things like aluminum refining where the temperatures are high enough to require "shielding". Likewise, for the more intense radiation fields the electronic devices selected need to be radiation tolerant - which we already do for space applications. We already build machines to move fuel assemblies around so we know how to do that. In a CANDU reactor those machines are handling fuel assemblies fresh out of the oven that are literally ten times more radioactive than the spent fuel in a reprocessing plant. The types of operations to be done include:
mechanical disassembly
dissolving in HF acid
pumping off the gases
fluorinating to remove the uranium
TBD to remove the plutonium
vacuum distill to recycle the processing salts.

Almost every one of these steps involve stuff that precludes humans nearby simply from the temperature and chemicals involved - totally independent of the radiation.

Once the people can't be right there then operationally I don't see the difference whether they are 10 feet away at a local terminal or in a separate building 1km away. So why are there people in the building at all?


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 21, 2014 5:11 am 
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Radiation level in space isn't that bad. Most of the interplanetary space in our solar system is below the threshold dose of 2 mSv/day (this is the dose per day above which significant reduction of life expectancy starts to happen). When handling spent fuel you have to think on the order of >20000 mSv/day.

Still we can make instruments inside nuclear reactors work so we should be ok with basic instrumentation. If you want fully automated robotics, with complicated digital systems, to handle the spent fuel, now that's a different story...


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 21, 2014 11:22 am 
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Seems like we need sensors to work (pressure, flow, temp) and valves and equipment to do take apart fuel assemblies. We are in a very controlled environment so I don't see the need for lots of local digital processing. If something complicated needs to be calculated do that on the other side of shielding. I bet we could design this with no electronics at all in the radiation field.

Do you think there would be any problem with electrical motors?


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 21, 2014 11:42 am 
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Reprocessing is one activity where maximum mechanization and automation is desirable. Industrial scale reprocessing is carried out in UK, France, Russia, Japan, China and India. It is done with a view to recycling of spent fuel. S. Korea is a candidate.
Aqueous reprocessing Purex is in general use. Pyro-processing was carried only experimentally in the US, as far as I am aware. Proliferation concern is a false bugbear in processing of used LWR fuel.
http://www.world-nuclear.org/info/Nucle ... lear-Fuel/


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 21, 2014 1:26 pm 
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Lars wrote:
Seems like we need sensors to work (pressure, flow, temp) and valves and equipment to do take apart fuel assemblies. We are in a very controlled environment so I don't see the need for lots of local digital processing. If something complicated needs to be calculated do that on the other side of shielding. I bet we could design this with no electronics at all in the radiation field.


If that can be done, yes it would be quite feasible. I suppose there is no reason for the CPU etc. to be in the cell.

Quote:
Do you think there would be any problem with electrical motors?


Depends. If just gamma and low temperature, then it is quite doable. So if you can wait a while and reprocess then you only have gamma and it would be ok.

If you have neutron or other high LET radiation, it gets tricky fast. High temperature certainly doesn't help. Most problems can be solved with advanced ceramic winding insulation. Magnetically sealed pumps, among the most attractive ones, unfortunately position the windings perilously close to the coolant.


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 21, 2014 2:36 pm 
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And no CCD sensors in the cell. Which means no machine vision. Even simple photocells have problems.


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 21, 2014 11:17 pm 
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You can't pipe the imaging via fiber optics to a sensor outside the hot cell?


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 22, 2014 2:36 am 
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Asteroza wrote:
You can't pipe the imaging via fiber optics to a sensor outside the hot cell?


Yes this should be possible. For really high doses of high LET radiation though most glasses will become micro-cracked or otherwise "foggy" (not sure what the technical term is). Perhaps a zircon or beryl/chrysoberyl glass fiber would do, or even some fluoropolymer fiber. For reprocessing of reasonably cooled down material you only have to deal with low LET radiation that is much easier.

Self-calibration electronics of robots may be more difficult but should also be possible with fiber optics.


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 Post subject: Re: Korean Reprocessing
PostPosted: Jul 22, 2014 8:02 pm 
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Neutrons should fade away within 10 - 20 minutes after the fuel is removed from the core. No problem with waiting that long. In fact, the particular application I'm thinking of would have a 4 year cool down period. So I'm thinking we are not in a high LET field.

I see no reason the motors themselves should be in a high temp environment. The fuel salt needs high temp for some steps but the motor can be placed a bit away and the fuel salt insulated.


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