Plutonium toxicity questions

[oldsloguy]

First Post, Great Site. Appreciate your ideas!

We always hear that plutonium is the most toxic material on earth. The reasoning as I understand it, is that plutonium oxide has many particles which are in the 0.1 micron or so range. Particles of this size are not removed from the lungs very well when they are inhaled and thus create “Hot spots” for long periods where the radiation dose is so high that cancer formation is almost certain after a lag time of 15 to 30 years.

The only way I know of producing this type of Pu oxide is by oxidizing metallic Pu. I am however not very familiar with the intermediate steps in the PUREX process, but my intuition is that in a wet chemistry process it would be unlikely or even impossible to produce this type of fluffy oxide. So,

#1 Is there any reason to think that in reprocessing nuclear fuel it would be possible to produce this type of fluffy oxide?

Further, once the Pu has been complexed into a ceramic with uranium, the resulting Mox would be very stable and toxicity wise very benign since ingesting it in any way would be nearly impossible.

#2 Is this correct?

Lastly, Health Physics Journal articles I’ve found (ref. below) indicate that the “Hot spot” hypothesis itself is nonsense. In one case, 25 WWll Los Alamos Pu workers inhaled varying amounts of fluffy Pu oxide. “Hot spot” would have predicted over 200 cancers in each worker. As of the early 1980”s none had a lung cancer. Overall mortality; lower than the general population.
Health Physics (Vol. 32, pp. 359-379, 1977), Health Physics, Vol. 48, No. 3 (March 1985), pp. 249-259.]

#3 Is there any reason to think that Pu is any more toxic than any of the other actinides?

Thanks for helping me understand this!

 

[Astronuc]

Firstly, Pu isotopes do not have the highest radiotoxicity. Shorter half-life isotopes of the heavier element are certainly more toxic in that respect. But then Pu is produced in much greater quantitites, so there is perhaps a greater chance to come in contact with the substance. In addition, transuranics are heavy metals, and heavy metals (e.g. Pb, Hg, . . .) can cause nerve damage if ingested. Elements chemically similar to Ca (e.g. Ra) can get taken up by the bones and thus represent a risk of sarcomas or problems with the hematological/hematopoietic system.

Purex refers to a wet extraction process in which Pu is separated from spent fuel (or U-targets). That is just the front end of the process for making Pu fuel or MOX. The Pu compounds (Pu nitrate or oxalate) are eventually calcined to Pu oxide or blended in solution with similar U compounds to form a U,Pu mixture, which are subsequently calcined. Ultimately MOX is usually formed if the fuel is being fabricated for LWR systems, and perhaps Fast Reactor fuel.

In terms of MOX production, there are wet processes, in which solution of Pu and U compounds (nitrates or carbonates) are blended, and there a dry processes in which oxides are mechanically blended, usually in two-step process of master blend followed by dilution blend. The wet process requires strict control to prevent criticality, while the dry process requires strict control for homogeneity. The latter increases the risk of dust or particulates which could be inhaled.

Ceramic grade oxide fuel is typically used in the geometry of a right circular cylinder (pellet/tablet) and sometimes the pellets are oversized in which case they are ground to spec. The grinding dust represents a hazard. I should point out that work on Pu compounds is done in a glove box or sealed (remote handling) environment, at least in the US, Europe and Japan.

As for the folks at Los Alamos, their situation would depend on the isotopic vector of the Pu, and the form metal dust or oxide that was inhaled. I don't know the specifics, so I can't provide any definitive comments.

 

[oldsloguy]

Thanks for the information. It's amazing how quickly you were able to do it! When I have a little more time, I'd like to follow up with a little more discussion on the subject. Thanks again.

 

[mgb_phys]

We always hear that plutonium is the most toxic material on earth.

Botulinum and tetanus toxins are fatal at less than 1ng/kg so 500g would be enough to kill everyone in the world. It takes 10x as much pu to make a single nuclear weapon!

 

[vanesch]

Botulinum and tetanus toxins are fatal at less than 1ng/kg so 500g would be enough to kill everyone in the world. It takes 10x as much pu to make a single nuclear weapon!

In fact, although I certainly won't deny that plutonium is very toxic, there are some properties of the material which makes that it is less of a "global danger" than often is claimed. The main reason is that plutonium doesn't spread easily. Also, eating plutonium is far less dangerous than inhaling it because its biological half time is in that case much lower (it gets quickly excreted). So the only really dangerous form of plutonium is a fine aerosol which you can inhale. Well, there are two properties that make that plutonium doesn't like being in an aerosol: first of all, it has a very high density (10 to 20 times denser than water), so it quickly drops to the floor, and second, several Pu compounds actually very easily bind chemically to materials in most soils ; clay for instance, but many other materials. Of course, close to a source of plutonium particles it is dangerous (like in a factory that handles plutonium powder and so on), but it isn't something that is going to spread easily over large regions.

 

[mgb_phys]

As astronuc already pointed out pu isn't much of a danger as anything other than an a fine dust - and pretty much everything is dangerous as a fine dust.

The was someone who offered to eat several grams of pu if his anti0-nuclear oponent would eat the same mass of caffeine. The low chemical afinity and radioactivity of pu meant that if it as in a single lump it would be relatively harmless.

 

[Astronuc]

I met one of two people who were involved in separate glove box explosions that resulted in in particles and solution of Pu compounds being imbedded in them. He was in his 60's approaching retirement, and after about 20+ years, he had no indications of adverse affects on his health.

 

[oldsloguy]

The was someone who offered to eat several grams of pu if his anti0-nuclear oponent would eat the same mass of caffeine. The low chemical afinity and radioactivity of pu meant that if it as in a single lump it would be relatively harmless.

I think the person you are referring to is Bernie Cohen. Professor Emeritus of Physics, University of Pittsburgh. An excerpt from Nuclear Energy, Karl Otto Ott and Bernard I. Spinard, eds., New York: Plenum Press, 1985 is available on the web at “russp.org/BLC-3.html”. Bernie describes the caffeine calculation and his bet with Ralph Nader.

Interesting, in looking for that website, I inadvertently found a discussion of the subject in the archives of this forum at “physicsforums.com/archive/index.php/t-156042.html”. A couple of the folks made an interesting computation of the dose received from ingesting 13 g of Pu (ref “thecandyman”). 13 g was picked since that is a borderline fatal dose of caffeine. I think the calculation is in the ball park as far as it went. I get a total of a little over 30 instead of 26 GBq, but no quibble. However, if I read that and the other posts correctly, the dose was assumed to be deposited into the entire stomach contents of 3 Kg, if the Pu was ingested as a fine powder. I would argue however, that most of this would be deposited in the stomach contents. So, assuming an intestine diameter of 3cm and a 5 Mev alpha range in water of 0.016 cm (scaled 20/1 from 8 x 10 –6 in uranium in one of the other posts which have no reason to dought). Thus only the alphas in the outside .016 cm of the intestine contents could reach the wall. As such, assuming only ½ of those directed outward into the intestine, the fraction of total dose reaching the wall would be:

Dwall = ½ * (Pi/4)*(do^2 – di^)/(Pi/4)*(do^2)
= ½ * 0.785*(3^2 – (3^2*0.016)^2))/ 0.785*(3^2) = ~ 2%

Dwall = fraction of alpha which is subtended by the first few thousand inches of the intestine wall
do = diameter of intestine
di = diameter of intestine contents where alphas emitted cannot reach intestine wall

This would reduce “thecandyman”s” estimated intestine dost to about 0.5 gray/hr. Assuming clearing of the intestine in say 10 hours the total dose would be about 0.5 gray, borderline fatal to the first few thousanths of an inch of intestine wall. I don’t know if killing the first few thousandths of wall would kill you or not, but my guess is that it may borderline fatal. Heck of a blistery sunburn kinda mess anyway!

Assumption: which I think is good is that to little Pu will be absorbed through the intestine wall to cause any significant addional radiotoxicity or heavy metal toxicity to the rest of the body.

Did I do that right??

 

[Astronuc]

What isotope or isotopic vector of Pu was used?

Certianly a powder or solution would be much worse than a solid pellet, with the pellet producting less exposure due to self-shielding, and less likely to be transported elsewhere outside of the alimentary canal.

 

[daveb]

The ALI for oral ingestion of Pu-239 is 0.8 microcuries for the surface of the bone (CDE) and 1 microcurie for the CEDE. This corresponds to about 16 micrograms. Note that this assumes the Pu-239 decays entirely in the body over the next 50 years. Depending on the chemcial composition of the plutonium, it may have a very small biological half life. Certainly a solid chunk has a very small biological half life. However, compounds such that the bonds are broken and the plutonium (since it is an actinide and bone marrow seeker) would irradiate the bone (hence the ALI for bone surface).

So, yes, essentially it depends on what chemical and phsyical form you swallowed.

 

[oldsloguy]

I assumed that PuO2 (239) powder would be uniformly mixed in the intestinal contents. PuO2 because it would seem to be the most common contaminate and powder the worst case. Also assumed is that any intestinal barriers such as mucous were too thin to stop the alphas. Actually, a little more digging yielded a couple of interesting things. I found a long ignored copy of the National Academy of Sciences BIER IV (my guess, minimal changes in BEIR VI) on my wife’s bookshelf which states the following on Page 309:

“Ingestion of alpha emitters is not considered a radiological hazard to the gastrointestinal tract since the range of the alphas is insufficient to penetrate the mucus and intestinal contents and reach the crypt cells.” Page 308 also pointed out that absorption through the gastrointestinal tract would be about 1 x 10 e-5 for Pu Oxide.

A DOE data sheet on the web, which appears to have been produced by Argonne NL
(//consolidationeis.doe.gov/PDFs/PlutoniumANLFactSheetOct2001.pdf) predicts ingestion at 5 x 10 e-4. This data sheet also has a table of simplified cancer induction coefficients (roughly 1.3 x10 e-10 cancers per ingested pCi). Thus, in Bernie Cohens challenge to Nader (13 grams, the LD50 for caffeine):

Probability of cancer = ingested grams * Ci/g * cancers/ Ci ingested

Cancer chance = 13 g * .063 Ci/g * 1.3 x 10 e-2 Cancers / Ci ingested

Cancer Chance = ~1% (and even that 20+ years later)

Bernie didn’t even give Nader a close to even chance!

It appears that the inhalation risk for cancer induction is only about 50 times greater than the ingestion risk if I am reading the ANL/DOE table correctly. I have some additional interesting information on inhalation, which I’ll post when I have a little more time.

The ANL/DOE data sheet also reiterates Vanesch’s excellent point (posted above), that being in my interpretation of it, you would almost have to design a system and material composition to cause a wide spread exposure to the general population.

I’ve based the above on Pu239 as the predominant isotope. One of you guys must be familiar with the fraction of Pu238 (the only isotope with a significantly higher specific activity) in spent reactor fuel or MOX.

 

[vanesch]

I

A DOE data sheet on the web, which appears to have been produced by Argonne NL
(//consolidationeis.doe.gov/PDFs/PlutoniumANLFactSheetOct2001.pdf) predicts ingestion at 5 x 10 e-4. This data sheet also has a table of simplified cancer induction coefficients (roughly 1.3 x10 e-10 cancers per ingested pCi). Thus, in Bernie Cohens challenge to Nader (13 grams, the LD50 for caffeine):

Probability of cancer = ingested grams * Ci/g * cancers/ Ci ingested

Cancer chance = 13 g * .063 Ci/g * 1.3 x 10 e-2 Cancers / Ci ingested

Cancer Chance = ~1% (and even that 20+ years later)

Well, there's something wrong here: if the mortality rate is 1.3e-10 per ingested PICO curie, (that's 1e-12 Ci), then the mortality rate is 130 per ingested Curie, and not 0.013. You're a factor of 1e4 off here.

That brings us to 13g x 0.063 Ci/g x 130 = 106.5, where the trick doesn't work anymore because we don't have small probabilities (one should use an exponential and not its linearized version). So you're pretty sure to be dead !

Also 0.063 Ci/g is for pure Pu-239, but reactor plutonium contains other isotopes, so this can easily be 10 or 100 times bigger.

In other words, no way I would eat 13 g of plutonium! Now, 13 g is a big quantity: about 26 average-sized aspirines!

 

[Astronuc]

I’ve based the above on Pu239 as the predominant isotope. One of you guys must be familiar with the fraction of Pu238 (the only isotope with a significantly higher specific activity) in spent reactor fuel or MOX.

The plutonium isotopic composition of used MOX fuel at 45 GWd/tU burnup is about:
37% Pu-239,
32% Pu-240,
16% Pu-241,
12% Pu-242 and
4% Pu-238.

Ref: World Nuclear Association - http://www.world-nuclear.org/info/inf29.html

Pu - http://www.world-nuclear.org/info/inf15.html

WG MOX would have less Pu-238.

 

[oldsloguy]

Well, there's something wrong here: if the mortality rate is 1.3e-10 per ingested PICO curie, (that's 1e-12 Ci), then the mortality rate is 130 per ingested Curie, and not 0.013. You're a factor of 1e4 off here.

That brings us to 13g x 0.063 Ci/g x 130 = 106.5, where the trick doesn't work anymore because we don't have small probabilities (one should use an exponential and not its linearized version). So you're pretty sure to be dead !

Also 0.063 Ci/g is for pure Pu-239, but reactor plutonium contains other isotopes, so this can easily be 10 or 100 times bigger.

In other words, no way I would eat 13 g of plutonium! Now, 13 g is a big quantity: about 26 average-sized aspirines!

Your right! That will teach me to write it down on paper rather multiplying in my head and typing. At first I thought I was saved by having forgotten the ~10e-4 factor of absorbtion through the intestinal tract, however I think the ANL table means ingestion at the mouth. Valid point about the linear response coefficient, however ANL picked the linear coefficient off the dose response curve, I don't think there is a way to save the argument. Maybe, Dr. Cohen was considering a pellet to limit dissolution. Unfortunately we are heading out the door for a week vacation. Out of curiosity I may send Dr. Cohen an e-mail when I return.