Plutonium's unusual interactions with clay may minimize leakage of nuclear waste

Nov 03, 2011

As a first line of defense, steel barrels buried deep underground are designed to keep dangerous plutonium waste from seeping into the soil and surrounding bedrock, and, eventually, contaminating the groundwater. But after several thousand years, those barrels will naturally begin to disintegrate due to corrosion. A team of scientists at Argonne National Lab (ANL) in Argonne, Ill., has determined what may happen to this toxic waste once its container disappears.

"We want to be sure that nuclides (like ) stay where we put them," says Moritz Schmidt, an ANL post-doctoral researcher who will present his team's work at the AVS Symposium in Nashville, Tenn., held Oct. 30 – Nov. 4. Understanding how these radioactive molecules behave is "the only way we can make educated decisions about what is a sufficient repository and what is not," he adds.

Plutonium, with its half-life of 24 thousand years, is notoriously difficult to work with, and the result is that very little is known about the element's chemistry. Few labs around the world are equipped to handle its high radioactivity and toxicity, and its extremely complicated behavior around water makes modeling plutonium systems a formidable task.

Plutonium's extraordinary chemistry in water also means scientists cannot directly equate it with similar elements to tell them how plutonium will behave in the environment. Other ions tend to stick to the surface of clay as individual atoms. Plutonium, on the other hand, bunches into nanometer-sized clusters in water, and almost nothing is known about how these clusters interact with clay surfaces.

To better understand how this toxic substance might respond to its environment, the Argonne team examined the interactions between plutonium ions dissolved in water and a mineral called muscovite. This mineral is structurally similar to clay, which is often considered for use in waste repository sites around the world due to its strong affinity for plutonium. Using a range of X-ray scattering techniques, the scientists reconstructed images of thin layers of plutonium molecules sitting on the surface of a slab of muscovite.

What they found was "very interesting," Schmidt says. The Argonne scientists discovered that plutonium clusters adhere much more strongly to mineral surfaces than individual plutonium ions would be expected to. The result of this strong adherence is that plutonium tends to become trapped on the surface of the clay, a process which could help contain the spread of plutonium into the environment.

"In this respect, it's a rather positive effect" that his group has observed, Schmidt says; but, he adds, "it's hard to make a very general statement" about whether this would alter the rate of plutonium leaking out of its repository thousands of years from now.

Schmidt cautions that these are fundamental studies and probably will not have an immediate impact on the design of plutonium-containing structures; however, he stresses that this work shows the importance of studying plutonium's surface reactivity at a molecular level, with potential future benefits for nuclear waste containment strategies.

"This is a field that is only just emerging," Schmidt says.

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More information: The AVS 58th International Symposium & Exhibition will be held Oct. 30 – Nov. 4 at the Nashville Convention Center. Presentation AC+TF-ThA-1, "Plutonium Sorption and Reactivity at the Solid/Water Interface," is at 2 p.m. on Thursday, Nov. 3.

Provided by American Institute of Physics

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ShotmanMaslo
3.6 / 5 (5) Nov 03, 2011
Nuclear "waste" of today is in fact an extremely energy-dense resource, if which only 1 % was burned in the reactor. It may prove to be very valuable in the future.
Doug_Huffman
2.3 / 5 (3) Nov 03, 2011
The reason it is waste (without the scare-quotes) is that it is vastly neutron absorbing poison providing sufficient negative reactivity to shutdown its reactor. Yes, there may be some fissionable fraction but too small and too expensive to recycle, else it would be recycled.
antialias_physorg
5 / 5 (3) Nov 03, 2011
But after several thousand years, those barrels will naturally begin to disintegrate due to corrosion.

Several thousand? Try thirty.
Asse nuclear deposit (in germany) where such steel containers have been dumped is already leaking - and it's barly 30 years in use.
Asse is an old, abandoned salt mine - said to have an ideal climate for preventing corrosion (very dry). If such 'ideal' sites are already leaking in a country that is not exactly known to be at the bottom of the tech-tree when it comes to manufacturing storage units, then imagine what would happen if nuclear reactors and waste deposits were in widespread use in countries that are not so conscientious about their surveys/procedures.
ShotmanMaslo
3.2 / 5 (5) Nov 03, 2011
Yes, there may be some fissionable fraction but too small and too expensive to recycle, else it would be recycled.


Nuclear fuel is very cheap, there is little incentive to recycle. But yes, it is sometimes recycled:

http://en.wikiped...ocessing

And I dont know about actually stored nuclear waste, but nuclear waste coming from the reactor has very high theoretically fissionable fraction, only a few percent at most are actualy burned in the reactor.
ShotmanMaslo
1 / 5 (2) Nov 03, 2011
Of course you may have to use different neutron spectrum to extract the rest of the energy.
Doug_Huffman
not rated yet Nov 03, 2011
Of course you may have to use different neutron spectrum to extract the rest of the energy.
Right.
...providing sufficient negative reactivity to shutdown ITS reactor.
Different neutron spectrum means recycling in a different reactor.

Who fails to do arithmetic is doomed.
typicalguy
3 / 5 (2) Nov 03, 2011
There was a scientific American article a year or two ago about reprocessing and reusing nuclear waste until it was reduced to a less dangerous material. The US was never going to attempt this because the infrastructure investment would cost hundreds of billions of dollars. (this is the end of the article summary - personal political statement incoming) One political party in the US hates infrastructure spending so this will never happen.
that_guy
5 / 5 (3) Nov 03, 2011
Actually, there are two main reasons the US does not recycle it's fuel.

1. The fuel we use in our commercial power plants is not weapons grade. Therefore, if it is stolen, it is harder to make into nuclear bombs.

Recycled fuel has a higher plutonium content and has to be 'burned' differently, and is easier to make into weapons.

2. Recycling nuclear fuel is expensive, as are the plants required to use recycled nuclear fuel.

3. Our politicians are idiots.

France recycles its nuclear fuel and has very little nuclear waste. It can be done relatively easily, although it is not excessively economical.

That said, the cost to store the concentrations of spent fuel for thousands of years changes the equation. But, power plants are not required to account for that cost.

Extra care needs to be taken to recycle fuel because of the chemistry of multiple radioactive components/elements, versus the straighforward process of enriching uranium ore.
KBK
1 / 5 (4) Nov 03, 2011
brown's gas (Rhodes gas) breaks down radioactive waste to utter perfection. A single 'liquifcaion' of any radioactive material, via browns gas, will drop it's radiation by 99%.

The reason you don't know it ..is that you are not supposed to as it opens a HUGE can of worms, for those who want to keep their stolen/hidden technologies, by force... in their hands only..

I have a 1600l/h browns gas generator.

I know exactly what I'm talking about, regarding the eradication of radiation.

The trick is for you to not yell and scream at me for saying such things, as that would be juvenile and illiterate animalism.

Instead, try to figure out how this molecular breakdown occurs..and also understand that I take risk by speaking out.

A note to the detractors is that I'd rather leave you to your own illiteracy and nastiness, but the world needs some truth out there. it's getting very ugly out there...and such things need to be brought forth.

To the silent thinkers: you are welcome.
antialias_physorg
5 / 5 (2) Nov 04, 2011
Instead, try to figure out how this molecular breakdown occurs..and also understand that I take risk by speaking out.

Certainly you take a risk: because it is not a molecular breakdown. We're talking radioactivity here, which is a matter of atoms and isotopes - not molecules.

You're very welcome to try to sell your 'truth' to the gullible, though. Should be some on this very board that will gladly pay you. Me, I'm sticking with physics.
rawa1
1 / 5 (1) Nov 04, 2011
"In this respect, it's a rather positive effect" that his group has observed, Schmidt says; but, he adds, "it's hard to make a very general statement"
Of course it is, because the same effect which slows down the leakage of plutonium from soil or clays would make their decontamination infeasible. In addition, it could lead to concentration of plutonium at the places, which we are not expecting by now.

The most of effective way, how to deal with nuclear waste is not to produce such waste, which is much easier by now, when cold fusion technology became available. We should solve the origin of problems, not their consequences.