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Enthalpy

Krypton-85 in our atmosphere

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Krypton-85 85Kr is a beta emitter with 687keV maximum energy and 10.7 year half-life. It's produced by uranium fission with 0.27% yield (137Cs and 90Sr: 6%). Here a report, a bit old and in French, but figures read the same in English anyway.

85KrIpsn.PDF

 

When reprocessing used nuclear fuel rods at La Hague, solid fission products like 137Cs and 90Sr and separated for storage, but 85Kr is just diluted and emitted in the atmosphere. For instance in 1999, La Hague emitted 2.9*1017 Bq of 85Kr, more than the radioactivity of 137Cs and 90Sr released by the Chernobyl disaster.

 

Iodine, caesium, strontium radioisotopes fall on the soil more quickly and locally if emitted, and accumulate in the food chain. Krypton, as a noble gas, dilutes in the whole northern hemisphere's atmosphere, where in 2001 it added 1.2 Bq/m3, with 3/4 of it coming from La Hague - it must be worse by now.

 

How bad is such an added radioactivity, much smaller than natural sources anyway? It irradiates a human body by 4nSv/yr, or 500nSv/yr at the skin as beta rays don't go deep. No experimental data tells the effect of such a low dose; scientific near-consensus is to extrapolate proportionally from higher doses, taking 1% more risk of a fatal cancer per 0.2Sv exposure. Over 30 years, this adds only 6*10-9 risks of casualty - but for each of the 6 billion people in the hemisphere, meaning an estimated 36 casualties.

 

Note the 1% per 0.2 Sv is a whole-body average, but external beta rays damage essentially the skin. It seems that 500 nSv/yr at the skin is a bit worse than the deep 4 nSv/yr taken here.

 

Some people challenge that the risk is proportional to the dose; they want to see some dose threshold below which the risk vanishes. Among them is Areva, the operator of La Hague.

 

I consider that since 85Kr arrives from the power plants confined in fuel rods, keeping all 85Kr confined in some storage can't be that difficult. And to avoid three dozens possible deaths, it should be done, without arguing about risk models.

Edited by Enthalpy

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Since Kr is a noble gas, I suspect it's not as much of a danger since it would have a short biological half-life — there are no processes that take it up into the body and keep it there. And also because it's a noble gas, there isn't going to be a convenient way to collect it while reprocessing the fuel.

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36 casualties? Globally?

 

Not worth worrying about.

 

Take the money you would have put into the reconfiguration of the plant and instead invest it in... Oh, I dunno... Feeding the hungry. My money says you save more than 36 lives per year that way.

Edited by InigoMontoya

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"I consider that since 85Kr arrives from the power plants confined in fuel rods, keeping all 85Kr confined in some storage can't be that difficult. And to avoid three dozens possible deaths, it should be done, without arguing about risk models. "

 

Banning cars could be done, and it would save many more people do you think "it should be done, without arguing about risk models." as well?

Or do you accept that the models (which are actually risk/ benefit models) might be a better way to make the decision?

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The estimation of casualties result from 85Kr that does not accumulate in bodies, as stated.

Storing noble gas is done every day, for instance in bottles used for arc welding.

It wouldn't require to reconfigure the reprocessing plant. Storing 85Kr leeds a few containers of moderate size.

Which is also incomparable with cars, which do bring some serious benefits as opposed to a poison in our atmosphere.

 

As for the cost, I dare to maintain that several dozen lives are worth a few bottles.

Unless you find an arguably better model, this figure results from prudent and mainstream evaluation methods.

And how much money is spent to rescue a hostage in Colombia, or victims of an air wreck?

Would you answer them "better spend my money elsewhere"? Or are they more important because they have a name and a face?

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i seriously doubt that there are any deaths that could be directly attributed to Kr-85.

 

a signal of 6 parts per billion will be swamped by other environmental factors. 1.2Bq/per meter cubed is pretty harmless. I'd be fine with being exposed to that level of radiation all my life.

 

but wait! humans are FAR more radioactive than that naturally from carbon-14, potassium-40 and other radioisotopes which have nothing to do with nuclear power.

 

if you were to put a human in a room with 1.2Bq/m^3 krypton (and air) then the human is going to be far and away the largest source of radiation.

 

and this is discounting other exposures (both natural and artificial) to radiation.

 

you may be able to get a statistical number but that doesn't mean it is a REAL number.

 

statistically, there could be somebody standing on the back of an elephant shouting "I love pygmy marmosets!" in portuguese but I seriously doubt its happening right now.

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"It wouldn't require to reconfigure the reprocessing plant. "

Yes it would.

They are not designed fo trap the stuff. Some sort of trap would need to be added (and it's not particularly easy to trap inert gases).

 

"Which is also incomparable with cars, which do bring some serious benefits as opposed to a poison in our atmosphere."

You seem to have missed something

http://en.wikipedia.org/wiki/Carbon_monoxide_poisoning#Suicide

 

The big issue here is that it would be silly to spend millions capturing Kr to save a dozen lives when you could spend the same money on, for example, better traffic control, and save many more lives.

Why are you not posting about speed cameras or providing measles vaccinations in the developing world?

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The estimation of casualties result from 85Kr that does not accumulate in bodies, as stated.

Storing noble gas is done every day, for instance in bottles used for arc welding.

It wouldn't require to reconfigure the reprocessing plant. Storing 85Kr leeds a few containers of moderate size.

Which is also incomparable with cars, which do bring some serious benefits as opposed to a poison in our atmosphere.

 

Storage isn't the problem. When separating Ar from the atmosphere you aren't trying to keep all the Ar from escaping. The process doesn't have to be particularly efficient, so the comparison doesn't apply. If radioactive Kr were useful for something, some of it could be recovered. Your position requires a large majority of it be recovered.

 

As for the cost, I dare to maintain that several dozen lives are worth a few bottles.

Unless you find an arguably better model, this figure results from prudent and mainstream evaluation methods.

And how much money is spent to rescue a hostage in Colombia, or victims of an air wreck?

Would you answer them "better spend my money elsewhere"? Or are they more important because they have a name and a face?

 

As InigoMontoya has implied, there is a cost/benefit analysis to be done. 6 fatalities per billion puts this way, way down on the risk table. If the money spent could save more lives spent elsewhere, why do this? You would be causing more deaths if you diverted money from more efficient efforts.

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A mole of 85Kr has 6E23 or so atoms in it.

In 10 years there will only be half of them left so the decay rate is of the order of 6E22 per year

that's 2E20 per day or about 2E15 per second

So 1E17 Bq is something like 100 moles of gas or about 2500 liters.

That's not going to be easy to find among all the air that goes through a large factory.

The idea of trapping it all simply isn't practical. (Though some is trapped for research purposes.

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I never told about trapping 85Kr from the atmosphere or separating it. 85Kr does get caught when the spent fuel claddings are opened, because releasing it at the plant would be deadly. It's all about storing the caught 85Kr, instead of diluting it for release.

 

This number of moles and volume is a good estimation, and storing such a volume is easy, yes. You're perfectly right.

 

As you all like to compare lives and costs, saving three dozen people at the price of a few bottles in a pool is very cheap.

 

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People who answer "I better spend my money to feed the hungry and vaccinate the poor" usually don't do it neither.

 

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Of course, other radioactivity sources are more intense than dilute 85Kr. But 85Kr does add its activity and its deaths.

You're telling basically "let's kill 36 people because they can't prove we did it". I won't follow you there.

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I never told about trapping 85Kr from the atmosphere or separating it. 85Kr does get caught when the spent fuel claddings are opened, because releasing it at the plant would be deadly. It's all about storing the caught 85Kr, instead of diluting it for release.

 

You have to contain it when it's released from the fuel and it has to be separated from the atmosphere when you do that.

 

As you all like to compare lives and costs, saving three dozen people at the price of a few bottles in a pool is very cheap.

 

That's not the only cost.

 

Of course, other radioactivity sources are more intense than dilute 85Kr. But 85Kr does add its activity and its deaths.

You're telling basically "let's kill 36 people because they can't prove we did it". I won't follow you there.

 

Nobody has said that. That's a gross mischaracterization of the arguments that have been presented.

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You have to contain it when it's released from the fuel and it has to be separated from the atmosphere when you do that.

When opening the fuel rod, you wouldn't first introduce atmospheric air in the gas going to be stored.

 

[Replying to Enthalpy's "The price of a few bottles in a pool is very cheap"]

That's not the only cost.

Sure.

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Enthalpy, your irresponsible use of electricity to communicate on this forum will directly contribute to an increase in greenhouse gases, rising sea levels and the drowning of an indeterminate number of Dutch. Will you continue with these unethical actions, or will you do the right thing and immediately forego the use of any electrical appliances?

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what about the carbon dioxide he's breathing out?

 

this is causing an indeterminate amount of flooding on some low rising pacific islands cause the mass relocation of thousands of people.

 

If you've every worked in a business or engineering, you'll have heard of pareto analysis.

 

basically, a little work on the major causes will give you a larger effect than a lot of work on the minor causes.

 

when your driveshaft is tearing its self free you don't spend millions of money developing new materials to make stronger bolts when you can spend less money getting it properly aligned.

 

same thing here, we have a problem (death) and many causes (radiation, disease, hunger etc.) why spend millions to save 6 people out of every billion when you could save 100's of people for only a few thousand.

 

worrying about Kr-85 at this moment in time would be utterly pointless when there are much bigger and more pressing problems. I suspect that by the time Kr-85 becomes the major health problem that it's half life would long ago have taken care of the problem.

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This number of moles and volume is a good estimation, and storing such a volume is easy, yes. You're perfectly right.

 

----------------------

 

People who answer "I better spend my money to feed the hungry and vaccinate the poor" usually don't do it neither.

 

--------------------------

 

Of course, other radioactivity sources are more intense than dilute 85Kr. But 85Kr does add its activity and its deaths.

You're telling basically "let's kill 36 people because they can't prove we did it". I won't follow you there.

 

Storing that volume would be easy.

Nobody ever said it wouldn't.

It doesn't matter what charitable donations anyone makes. You can still save more people for the same $ by doing other things.

I'm not saying nobody can prove that we killed those 36 people. I'm saying that we did it and we know we did (though we will never know which 36 it was- but that's not the point they are still dead no matter who they were.)

 

 

So that's 3 straw man arguments in one post.

I think that might be a record.

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Here an elementary example of a Krypton-85 storage, to give a general sense of its difficulty. I didn't and won't check how to catch 85Kr from the fuel rods; boiling nitrogen?

 

A tube of ID=0.17m and L=6m stores the 85Kr extracted during one mean week at La Hague, at absolute 0.95b if it were to reach +100°C. Bent in a U shape and immersed, it holds the gas even if a seal leaks.

 

post-53915-0-43604200-1322873485_thumb.png

 

Aluminium AA5083 is one interesting choice. 20mm walls and two thick welded plugs let it sink head up.

 

Betas of mean 251keV produce 223W directly in the wall, very easy to cool. The dose at the walls is several magnitudes below a fission reactor, and betas damage alloys little.

 

85Kr produces a 514keV gamma in 0.43% of the disintegrations. Bremsstrahlung in aluminium adds little. 20mm walls shield the gammas by a factor >60, so a human standing along the tube in air would get 0.1Sv in >20min.

 

The produced Rubidium-85 melts readily and the liquid might dissolve aluminium. Water in the tube would catch Rb but the alkali corrodes aluminium. A mild acid instead would still produce hydrogen, not so nice. I imagine a metal with varied valences solves that, like Iron in FePO4 becoming RbFePO4, or Prussian blue, or potassium ferricyanide - ask a chemist. Vacuum doesn't buckle the tube.

 

post-53915-0-26010800-1322873690_thumb.png

 

A pool of 12m*12m would store the 85Kr extracted during 15.4yr; this is enough if older, emptier tubes are re-filled with newer 85Kr, but I'd prefer a bigger pool and fewer operations. Some 3m water shield the gammas and cool the 180kW by natural convection of few dm3/s. An exchanger at one side suffices, easing crane operations. A direct exchanger with some 15m3/s air would be challenging, but heat pipes between the pool and the blown fins make it easy.

 

Marc Schaefer, aka Enthalpy

Edited by Enthalpy

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Oh nobody is denying that we could recover Kr-85 from reprocessing facilities, that isn't the issue.

 

The issue is: why bother?

 

even a simple setup like this is going to cost millions of dollars globally (largely in the qualification and validation stages) as you'd have to install them at EVERY reprocessing site in the world.

 

now, is it worth it for 36 cases where it is impossible to directly link (or even indirectly link) the deaths to Kr-85?

 

I'd say no.

 

Lets say we have a body lying on the table in the morgue. The patient died of lung cancer. How would you be able to tell if this cancer was caused by Kr-85? Why not smoking (either first hand or second hand)? Why not some C-14 in his own body? Why not the chest X-ray he had 20 years ago when he had an infection?

 

ALL of those example I gave you there would be considered the likely causitive agent BEFORE Kr-85.

 

And really, the only way atmospheric Kr-85 could kill is by cancer. There is never going to be a radiation poisoning death from it, never going to be an asphyxiation death from it and so on.

 

So really, you're wanting to look at carcinogens. Why not spend the money developing carcinogen free cigarettes? It's going to have a MUCH more massive effect than trapping Kr-85.

 

If you were a pilot would you worry about the fact that the yoke had a scuff on it if the plane was about to hit a mountain side? because really, thats the difference in impact we are talking about here.

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Here an elementary example of a Krypton-85 storage, to give a general sense of its difficulty. I didn't and won't check how to catch 85Kr from the fuel rods; boiling nitrogen?

 

Which is probably not a trivial problem.

 

 

Put in perspective, the total number of deaths per year is around 60 million (with more than half being caused, directly or indirectly, by malnutrition). So we're discussing a 0.00006% change in the death rate. And the argument is how to best effect such a change. Even if the recapture of Kr-85 were cheap and only cost $36,000 per year to operate (basically that's no equipment and one fairly cheap, skilled, industrialized-nation employee, so this is an exceedingly conservative number), I'll bet I could save 36 people from starvation for $1,000 each. There are areas where the poverty line is around $1 a day, so just handing this money over to them gives them more than double the poverty-line income. And the actual Kr-85 solution is undoubtedly more costly by a few orders of magnitude.

 

IOW, the argument is that this an optimization problem, not an engineering problem.

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You could just about keep the stuff in a plastic bag. That was never the issue.

What is difficult is the bit that you gloss over by saying "I didn't and won't check how to catch 85Kr from the fuel rods".

Unless you can answer that issue the idea is dead in the water anyway.

 

You would have a better effect on the overall death rate by spending the money on speed cameras or some such.

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Reprocessing plants for nuclear fuel, like La Hague, emit also tritium, which they dilute in the Ocean.

 

Here's data (for 1999 and in French, sorry, but figures read the same in English):

http://www.irsn.fr/EN/Research/publications-documentation/radionuclides-sheets/Documents/Tritium_H3_v1.pdf

 

The amounts are small, and I couldn't consistently estimate the risks for humans; it seems that significant risks would only result from a non-uniform dilution, for instance if the food chain absorbs tritium before it's fully diluted - and that's hard to model.

 

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Anyway, if tritium had to be stored, it looks rather easy.

 

Fine powder of dessicated alumina is sold like plaster, to be mixed with water and moulded in form by the user to make ceramic objects - I suppose the reaction produces Al2O3°3H2O, maybe with a hydroxide fraction. That's a stable, inert compound.

 

Make dilute superheavy water with the tritium. Let this water react with the dessicated alumina powder to obtain a ceramic, maybe the size of a tennis ball. Then, use normal water to add a 20mm cap of hydrated alumina around the ball, to absorb any Bremsstrahlung from the weak betas.

 

La Hague emitted 1.3*1016 Bq/yr of tritium in 1999; over 17.7yr this cumulates only 640g of pure tritium. If ten Al2O3 incorporate one tritium atom (for mechanical stability and against proliferation) it takes 340kg of ceramic balls which cumulate only 210W (5.7keV mean electron energy), emit no betas and very little gammas absorbed by shallow water.

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Since we didn't care about 3E17 Bq of 85 Kr we are not going to care about 1.3E 16 Bq of 3H

 

 

 

Incidentally, re " That's a stable, inert compound."

Not in the presence of water it isn't , so you would have to keep it away from air.

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how does it stack up with radiation hormesis? (I don't believe that has been proven wrong yet)

 

thats the kind of dosages where radiation could have health benefits by stimulating your damage repair centres causing your body to fair better than if you were exposed to a lower dose.

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Hello everybody!

Areva is supposed to build a plant in China to reprocess spent nuclear fuel (agreement hoped in Spring 2018).

I should like to remind that the radioactive 85Kr fission product, which stays in the fuel rods until they're opened, can be stored easily until it has decayed, as I described here (drawings on Dec 3, 2011) so there is no need to release it in our atmosphere.

This operation is easier to design in a new plant, so it's a good opportunity for improvement.

And: happy new year to everyone!

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