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 Post subject: Spent fuel activity
PostPosted: Mar 06, 2015 1:12 pm 
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The following graph from IAEA:

Image

Typically we (actually anyone except me) talk(s) about plutonium as the long lived waste storage issue. But, looking at the graph its only Am-241 that determines the longevity by the standard of uranium ore equivalents.

Is this true? If we get rid of americium and leave plutonium in, we're below uranium ore equivalent activity in <500 years?


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 06, 2015 1:49 pm 
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Another thing, that is of some value discussing, is what we count as risk.

Typically spent fuel risk is shown as ingestive toxicity. I've always resisted this idea because people generally don't try to eat ceramic materials. If they do, they will kill themselves pretty quickly on eating rocks. A more reasonable risk estimator is the gamma dose from a spent fuel assembly.

http://www.princeton.edu/sgs/publicatio ... t-2011.pdf

Looking at the data there's a 10x reduction every 80-100 years or so. Even with a high burnup PWR assembly, there's only a 1000 mSv/h field at 100 years, which means you get to below the treshold chronic dose of 2 mSv/day in less than 500 years. Basically you could put a 500 year old spent fuel assembly in your living room and it would pose negligible health risk!

That is a very different narrative than what we're usually fed (even by scientists in the field).


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 06, 2015 10:02 pm 
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This is why I doubt the usefulness of geological storage - it seems to be that surface storage for ~300 years followed by compaction (by OREOX) or full blown reprocessing is the best option.


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 07, 2015 3:36 am 
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E Ireland wrote:
This is why I doubt the usefulness of geological storage - it seems to be that surface storage for ~300 years followed by compaction (by OREOX) or full blown reprocessing is the best option.


Yes, that's exactly what the data suggests. Geologic storage means little control over cost, quality, modularity, schedule, recoverability, etc.

It amazes me though that you could stand next to a 500 year old spent fuel assembly without any health risk. It'll be about as dangerous as a can of paint. You don't hear that from Greenpeace or even from so called spent fuel storage experts.


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 07, 2015 7:19 pm 
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SO after 300 years the most dangerous item in the spent fuel is the same stuff we put in our home smoke detectors ?!??


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 07, 2015 7:38 pm 
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Good discussion here.

ORIGEN provides useful data for a better insight....

https://dl.dropboxusercontent.com/u/116 ... ORIGEN.JPG


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 07, 2015 7:40 pm 
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Also for radiotoxicity....

https://dl.dropboxusercontent.com/u/11686324/Radiotoxicity_in_water_ORIGEN_SNF(FP)-NU_parity.jpg


Last edited by jaro on Mar 08, 2015 3:31 am, edited 1 time in total.

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 Post subject: Re: Spent fuel activity
PostPosted: Mar 07, 2015 7:42 pm 
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A different view....

https://dl.dropboxusercontent.com/u/116 ... ORIGEN.jpg


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 07, 2015 9:33 pm 
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Joined: Nov 14, 2013 7:47 pm
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Location: Iowa, USA
This...

Cyril R wrote:
Looking at the data there's a 10x reduction every 80-100 years or so. Even with a high burnup PWR assembly, there's only a 1000 mSv/h field at 100 years, which means you get to below the treshold chronic dose of 2 mSv/day in less than 500 years. Basically you could put a 500 year old spent fuel assembly in your living room and it would pose negligible health risk!

That is a very different narrative than what we're usually fed (even by scientists in the field).


... is precisely what I got from the graph. I remember reading a "scientific" article while in high school about how linguists and archaeologists were teaming up to develop symbols to mark off our radioactive waste sites so that future civilizations won't kill themselves disturbing them. Had I known then what I know now about radioactive half life I'd have immediately known how this was not about science. I also would have more quickly realized why the magazine I read it from went out of print.

What it also tells me is that if we take out a handful of useful isotopes from the spent fuel that the radioactivity of the remains would be less than that of fresh fuel. My top four picks would be Cs-137, Sr-90, Am-241, and Np-237.

Cs-137 is a valuable radiation source in medicine and industry, such as radiation therapy and material thickness gauges.

Sr-90 can be used directly in radiothermal devices. Np-237 is a feedstock element for Pu-238 production, another valuable radiothermal element.

Am-241 is used in smoke detectors and less commonly as a radiothermal element.

If we can get enough people that won't wet themselves at the mere mention of plutonium that could also be processed out of the fuel. It's worthless for weapons as it is, too much Pu-240, but quite valuable as fuel. I don't know enough about how much Pu-239 has to be in the mix but from what I can see it looks like the plutonium processed out of the spent fuel might be suitable as seed fuel in a LFTR or similar reactor.

I'm reminded of the "rebranding" done in the coal industry. That stuff that comes out the bottom of a coal burning plant is no longer called "coal ash" or "coal waste", it's called "coal combustion products". What was once waste is now used for things like concrete aggregate and industrial abrasives. The nuclear energy industry also needs some good PR like that.

_________________
Disclaimer: I am an engineer but not a nuclear engineer, mechanical engineer, chemical engineer, or industrial engineer. My education included electrical, computer, and software engineering.


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 08, 2015 3:01 am 
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jaro wrote:
Good discussion here.

ORIGEN provides useful data for a better insight....

https://dl.dropboxusercontent.com/u/116 ... ORIGEN.JPG


This data is useful for analysis but not useful for conveying the risk of spent fuel to the public.

For that we'd have to point out the difference between ingestive toxicity vs actual radiation dose of standing next to a spent fuel assembly.

Sure we can dissolve the waste in H2O and feed that to humans. We can also dissolve cadmium telluride solar panels in water and feed that to humans. But its being silly. This isn't risk analysis, its hyperbole.


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 08, 2015 3:23 am 
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Cyril R wrote:
For that we'd have to point out the difference between ingestive toxicity vs actual radiation dose of standing next to a spent fuel assembly.

Sure we can dissolve the waste in H2O and feed that to humans. We can also dissolve cadmium telluride solar panels in water and feed that to humans. But its being silly. This isn't risk analysis, its hyperbole.

I tend to agree with that, and wonder about ways of presenting the issue effectively to the public.

I don't see a way of doing this in a very concise way (yet), but there is one thing that strikes me as relevant.

I have been following the posts of "Geology Page" on facebook for some time, and it's interesting how often the various mineral photos they post include toxic elements like Arsenic, Mercury, Lead, Barium, etc.
Obviously these natural minerals, often occurring at or near the surface, have a higher chance of dissolving in water than ceramic or glass HLW, encased in various corrosion resistant layers, and entombed 500m or more below surface.

For some of the TRUs the chemical toxicity might actually be a greater risk than their radiotoxicity.

Any ideas on how to condense all this into a simple meme ?

So far the only thing I've found useful is a graphic depicting "uranium face-painting" by native Americans, a century or more in the past:
https://www.facebook.com/49384377736219 ... 945831477/


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 08, 2015 4:43 am 
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If you want inspiration on how to convey the risk of a geological storage facility then the late Cohen's book, "the nuclear energy option" is brilliant. It looks at the amount of activity actually getting out if all engineered barriers fail and the repository instantly gets flooded. Turns out nothing actually gets out even in this extreme case, it gets stuck on rock. Oklo natural nuclear reactors confirm this.

But for our purposes the main thing is to get people to understand that we're not eating this stuff. It would be fun to look at the amount of houshold chemicals used in a lifetime, bleach, detergent, etc. and check how many "lethal doses" that amounts to. This will make people understand the difference between ingestive toxicity and risk.

For the spent fuel assembly, how about a graph where the bottom of the scale (y axis) is the safe dose level of 2 mSv/day @ 1 meter distance. The line would then reach the bottom at 500 years or so. Then insert a person standing next to a spent fuel assembly to show what this graph depicts. The title, "how long before it is safe to stand next to a spent fuel assembly?". It should not be a log scale, just linear. People don't understand log, plus it is impossible to read from.


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 08, 2015 4:48 am 
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We can also look at lead. The LD50 for lead for a male adult is less than 10 grams. So if you have lead plate roof-shingle cover-seal things (don't know what they're called in English) like I do, then you can calculate the lethality. In my case I have over 20 kg of lead plating, so that's enough to kill 1000 adults.

There's also the more pedantic joke that tomorrow's production of hat-pins could kill everyone on the planet, but it would cost a lot to pay all the surgeons to put it into everyone's hearts.


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 08, 2015 4:55 am 
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Kurt Sellner wrote:
This...

What it also tells me is that if we take out a handful of useful isotopes from the spent fuel that the radioactivity of the remains would be less than that of fresh fuel. My top four picks would be Cs-137, Sr-90, Am-241, and Np-237.

Cs-137 is a valuable radiation source in medicine and industry, such as radiation therapy and material thickness gauges.

Sr-90 can be used directly in radiothermal devices. Np-237 is a feedstock element for Pu-238 production, another valuable radiothermal element.

Am-241 is used in smoke detectors and less commonly as a radiothermal element.

If we can get enough people that won't wet themselves at the mere mention of plutonium that could also be processed out of the fuel. It's worthless for weapons as it is, too much Pu-240, but quite valuable as fuel. I don't know enough about how much Pu-239 has to be in the mix but from what I can see it looks like the plutonium processed out of the spent fuel might be suitable as seed fuel in a LFTR or similar reactor.


Nice in theory, but:
1. Demand for Cs-137 and Sr-90 will be significantly lower than what a decent nuclear program will produce.
2. Separating the various chemicals is a non trivial task. An entity which can master this task will also have the capability to produce weapons grade materials.

Ultimately the long lived Actinides need to be removed and used as fuel for reactors, and the fission products put somewhere for a few hundred years.

How does Am-241 perform in a reactor?

I think we ought to stop talking about nuclear "waste" having to be stored for millennia, and distinguish between "spent fuel", which is a valuable resource, and the "waste" which needs to be kept out of reach for a few centuries.

And this comes back to: How easy is to separate "spent fuel" from the "waste"?


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 Post subject: Re: Spent fuel activity
PostPosted: Mar 08, 2015 4:58 am 
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Cyril R wrote:
We can also look at lead. The LD50 for lead for a male adult is less than 10 grams. So if you have lead plate roof-shingle cover-seal things (don't know what they're called in English) like I do, then you can calculate the lethality. In my case I have over 20 kg of lead plating, so that's enough to kill 1000 adults.

There's also the more pedantic joke that tomorrow's production of hat-pins could kill everyone on the planet, but it would cost a lot to pay all the surgeons to put it into everyone's hearts.


I was talking to "faucet" companies this week and discovered that standard brass had up to 2% lead, up until the last decade - it's being phased out.

So even your plumbing (unless it's all from the last decade) - which you drink from - will have dozens of lethal doses of lead.


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