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A way to mop up nuclear accidents: Possible ?

I think the hard part is making the atoms into something that is less radioactive. one part of the disaster at the plant in japan seems to be related to plutonium 239 or 241, not sure which is there a way we could make it into something that decays slower or a stable isotope quicker than nature ?

what are anyones thoughts ?

The essential answer: No, it's not possible/reasonable.

First of all, in nuclear accidents you don't have nice separation of isotopes into groups you can deal with easily; you have tons of seawater with bits of U, Pu, etc. Second, breaking the atoms down making them more stable is essentially what reactors already do -- but the end results are still far from stable Pb. Third, even if you captured all the decay products there isn't an efficient way to decay them further.

**

It might be an interesting exercise to see how much radiation was released into the environment through this reactor's lifetime and compare that to the amount released by an equivalent gigawattage of coal plants.

[QUOTE=science_man_88;255366]also could we not find a alpha particle absorber ?[/QUOTE]

Sure! A car door, a CD cover, a sheet of construction paper... alpha particles are easy to stop. The main hazard is inhalation -- the particles are *really* heavy and can knock a lot of things out of place when they're in your 'insides'. The QF is usually quoted as 20 (essentially, at a given level of radiation, they're 20 times worse than gamma rays) but this probably understates their danger. I'm not sure whether all-new scholarship would suggest a QF closer to 25 or to 50, but almost surely it should be revised upward.

A tobacco plant is interesting, though, as it gathers up polonium and other minerals from the ground. Plants seriously have been investigated for low-level radioactive clean-up. As for alpha particles, the atom they were shot from tends to leave a "recoil track" in whatever material it was in. Beta particles tend to ionize things nearby, so again, the hazard is inhalation, and neutrons tend to activate (make radioactive) whatever they finally interact with.

Finally, don't forget that cosmic rays (super high energy photons and the daughters of their occasional interactions with the matter that surrounds us) aren't difficult to count even in nominally non-radioactive situations. Because of its nature, (a geiger counter can count single gamma rays) fantastically small amounts of radiation are detectable, even if it is hard to separate from the natural background.

[QUOTE=CRGreathouse;255364]The essential answer: No, it's not possible/reasonable.

First of all, in nuclear accidents you don't have nice separation of isotopes into groups you can deal with easily; you have tons of seawater with bits of U, Pu, etc. Second, breaking the atoms down making them more stable is essentially what reactors already do -- but the end results are still far from stable Pb. Third, even if you captured all the decay products there isn't an efficient way to decay them further.

**

It might be an interesting exercise to see how much radiation was released into the environment through this reactor's lifetime and compare that to the amount released by an equivalent gigawattage of coal plants.[/QUOTE]I beg to differ in several respects. Your last point is the easiest to deal with: the typical concentration of U and Th in coal (order of magnitude 1ppm and 10ppm respectively) is such that coal-powered electricity generation produces about the same amount of radioactive waste as do U or Pu powered fission generators. The major difference is that the latter's waste is concentrated enough that it may be stored in a small facility whereas the former's is so dilute (and consequently so bulky) that it is dumped back into the general environment.

In one sense your claim that reactors break down radioactive atoms of Pu and/or U into more stable ones is correct. The fission product nuclei have a smaller mass-defect than their progenitors --- that is where the useful power comes from via E=mc^2. However, and in my opinion, a much more important observation is that many of the fission products are markedly [B]less[/B] stable in the sense that the nuclei have a markedly shorter half-life than the billion years or so of the fuel isotopes. Their half-lives range from sub-milliseconds to millenia. The shortest lived isotopes we don't much care about --- those with a half-life of a day or less --- unless you happen to be one of the people directly on-site cleaning up the mess.

When everything is working normally, dealing with the isotopes with a half-life of less than a year is easy. Store them safely for a few years and the problem is largely solved. The "safely" bit includes keeping the storage cool while the radioactive heat decays away. That's one of the problems in the Fukushima incident.

There are several ways of dealing with the years to millenia isotopes. The simplest is to bury them somewhere harmless and leave them alone. (Actually, I suspect that we'd dig them up again after a relatively short time because they would by then have become useful raw materials.) The next simplest, and better in my opinion, is to put them in a high-neutron flux reactor. Neutron capture converts them into short-lived isotopes which decay rapidly, thereby reducing the problem to a case which has already been solved as the mathematicians would say. Needless to say, you could extract the heat produced by the process and use it for power generation.

Finally, a minor nit-pick. The end result of U and Pu fission is indeed "still far from stable Pb" but that's not a helpful comparison. That's because the atomic numbers of U and Pu are 92 and 94 respectively and fission products are approximately equal in size --- 40 < Z < 60 say. The atomic number of Pb is 82.

Paul

[QUOTE=Christenson;255376]A tobacco plant is interesting, though, as it gathers up polonium and other minerals from the ground. Plants seriously have been investigated for low-level radioactive clean-up. As for alpha particles, the atom they were shot from tends to leave a "recoil track" in whatever material it was in. Beta particles tend to ionize things nearby, so again, the hazard is inhalation, and neutrons tend to activate (make radioactive) whatever they finally interact with.[/QUOTE]

Yes -- though high-energy betas are also a proximity hazard (e.g., P-32).

Neutrons are scary because they're hard to detect. Usually when I deal with them I'm just monitoring the associated gammas.

[QUOTE=xilman;255400]In one sense your claim that reactors break down radioactive atoms of Pu and/or U into more stable ones is correct. The fission product nuclei have a smaller mass-defect than their progenitors --- that is where the useful power comes from via E=mc^2. However, and in my opinion, a much more important observation is that many of the fission products are markedly [B]less[/B] stable in the sense that the nuclei have a markedly shorter half-life than the billion years or so of the fuel isotopes. Their half-lives range from sub-milliseconds to millenia. The shortest lived isotopes we don't much care about --- those with a half-life of a day or less --- unless you happen to be one of the people directly on-site cleaning up the mess.[/QUOTE]

I was only addressing the particular claim of science_man_88. I'm well aware of the various half-lives of the decay products. The worst ones, as you intimate, are those with the moderate half-lives -- within an order of magnitude of, say, 20 years like polonium 209/208. The really short-lived ones can be allowed to decay, and the long-lived ones aren't that hot.

[QUOTE=xilman;255400]When everything is working normally, dealing with the isotopes with a half-life of less than a year is easy. Store them safely for a few years and the problem is largely solved. The "safely" bit includes keeping the storage cool while the radioactive heat decays away. That's one of the problems in the Fukushima incident.[/QUOTE]

Considering that I do this at work, I agree...

[QUOTE=xilman;255400]Finally, a minor nit-pick. The end result of U and Pu fission is indeed "still far from stable Pb" but that's not a helpful comparison. That's because the atomic numbers of U and Pu are 92 and 94 respectively and fission products are approximately equal in size --- 40 < Z < 60 say. The atomic number of Pb is 82.[/QUOTE]

Fair enough. I was really thinking of the [url=http://upload.wikimedia.org/wikipedia/commons/4/4e/Uranium_series.gif]decay series[/url] via U-234 but that's normal decay, not fission. (We don't do fission, only biomed.)

[QUOTE=CRGreathouse;255404]Considering that I do this at work, I agree...[/QUOTE]I no longer do this sort of thing professionally. However, I was working at the Unclear Physics department at Oxford University when Chernobyl released its radioactivity. The people there had no problem at all picking up the medium half-life isotopes from the lab roof but given that we had the equipment and expertise to find single atoms that was no surprise at all. I played no active role in that particular activity though it was, of course, a matter of tea-room conversation. My activities included writing control software for a linac and other software to simulate a neutrino telescope.

IIRC (it's now 25 years since I last worked there) we used BF_3 to detect low energy neutrons. Not sure what the currently favoured technology may be but Google will doubtless tell me if I ask nicely.

Paul

I think the current state of the art for low-energy neutron detection is to use helium-3; but we only have helium-3 because the US and USSR made lots of atom bombs with tritium boosting and the tritium turns to He-3 in the medium term, and the demand for neutron detection to ensure that the frequency of atom bombs in containers entering the USA is as low as attainable is such that they're going back to using BF3 which can be made out of boron and fluorine in normal chemistry labs.

Fine for me; save He-3 for the exciting cryogenics applications which can use nothing else but couldn't possibly afford for lithium to be irradiated and the tritium stored for two decades to make He-3.

[QUOTE=CRGreathouse;255364]
It might be an interesting exercise to see how much radiation was released into the environment through this reactor's lifetime and compare that to the amount released by an equivalent gigawattage of coal plants.[/QUOTE]

[url]http://www.scientificamerican.com/article.cfm?id=coal-ash-is-more-radioactive-than-nuclear-waste[/url]

is the only thing I've found that scares me so far.

though this is a google look into a power plant:

[QUOTE=http://www.google.ca/search?sourceid=chrome&ie=UTF-8&q=coal+plant+radiation;]Fossil fuel power station - Wikipedia, the free encyclopedia
Just one accident like Chernobyl can release 35 times as much radiation in 10 days as the total radioactive emissions from coal power plants on the entire ...[/QUOTE]

I checked for this in the article and found nothing.