Name: 【地層処分の科学】1-2. 放射性核種のガラス固化
Uploaded: 2026-01-03T03:20:13.000Z
Duration: 10 min 39 s
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So we have learned until now that we need to isolate the fission products and to fix them in something better than a tank where we put them in.

So we make out of the fission products a solid.

We cannot just dry them and there will be too much heat produced.

So we need to have a matrix, a solid matrix where we can put the fission products in maybe 10, 20% of fission products and 80% of additives of some other solids, so that it becomes some really strong solid phase.

As solid phase, we can have either amorphous or crystalline substances.

Amorphous just for explaining what it is.

Amorphous is a structure which is aperiodic.

Distances are different between the different atoms.

And possible in such an amorphous structure to fix atoms of very different types.

And the fission products which are produced by the nuclear reaction, they have all sizes of all different sizes because they cover essentially the whole periodic system.

So you have alkali elements, alkali earth elements, you have rare earth elements.

And all of them are radioactive, or many of them are radioactive.

And then these need to be fixed in some structure which covers all of them.

We could also there the amorphous structure has really an advantage because we can put sufficient products of different size in crystalline products seems to be a little bit stable.

So in amorphous, Some amorphous solids could transform into crystalline 1.

The distance between the atoms are normally much more fixed.

They are smaller and larger bond distances and so on.

And some radionuclides can be nicely incorporated into such crystalline structures, but

many cannot, because if you have a whole series of different sizes of atoms, it's difficult to put all of them in one single crystal.

So what we do, one would need different crystals for each of the radionuclides.

We prefer on the scientists which have worked on this since some 50 years, they come up with borosilicate glass as the worldwide best choice.

And there's now also industrial, large industrial experience of fabricating such borosilicate glass.

You see here at the top in this image, just a sketch of how a borosilicate glass may look at, maybe looked at from the size of the atomic distances.

So the atoms you see, they are very large different cages at different distances.

You have oxygen, you have silica, you have boron, you have aluminum.

These all are glass making substance that produces somehow the glass.

And then radionuclides which you see at the bottom of this diagram, little PF would then be fission product.

They could be incorporated in this structure and into this.

So you have the silicon oxide, boron oxide.

essentially the linking between silica and boron, between silica and aluminium, between aluminum and sodium, there's always some oxygen atoms in between, because this is all oxides which are somehow molten to form a borosilicate glass.

And of course there are some boron, that's what borosilicate means, and silicium as some main elements.

But of course the principal element is oxygen in such a gas network.

So it's a uni cost phase for minor actinides like americium neptunium, for fission products like cesium 137, strontium 90, technetium 99, iodine 129 and so on.

Activation products are inactive substances which by neutrons coming from a nuclear reactor, from the nuclear fission become activated.

So they are active, they are also radioactive and they also need to be fixed in such a structure.

So these radionuclides are very dangerous for hundreds of thousands of years.

So the glass which we produce should also be stable for hundreds of thousands of years.

Normally, if you look in nature, you see many solid phases, you see minerals, you see even natural glasses.

And some of them are millions of years of stable.

Some they are produced by volcanoes and so on, and they have very long stability.

And if the radionuclides would be in such a structure, that will be very good fixed.

Now, going more in detail, what is a glass structure?

This is essentially only silicon dioxide in a more aperiodic way of arrangement.

You see here some larger cages and smaller cages, but it's rather difficult to incorporate in this radionuclides.

It's very stable relative to water, for example, relative to groundwater.

But the melting temperature is very high.

It and it's difficult to make an industrial process at 2000 degrees, in which case you still are able to put radionuclides into such a structure.

And so it's much easier to take borosilicate glass.

And you can put radionuclides inside, into this structure, as is indicated here, with this black points.

Principally then you have breaking bonds by sodium and bridging Oxygen.

You have open oxygen bonds and you find lots of oxygen cages where somehow the radionuclides are surrounded by oxygen and fixed inside of this glass network.

So the fission products, they become an integral component of the glass.

Like the sodium is part of the glass, like the silicon is part of the glass.

The fission products which are now inside of the glass are also part of the glass.

These glasses are quite often black, so the radionuclides give it also some kind of a color.

So how are these radionuclides fixed in the glass?

We have coordination environment, for example, of tetravalent plutonium.

And coordination environment means to have the oxygen cage inside of the glass, the oxygen binding structure, where is the plutonium in and how much bonds.

It's linked to the glass network, it's about eight.

For uranium four, it's about six to eight.

For example, you see the thorium inside of the glass structure with a distance of oxygen atoms in all directions.

And then this is linked to the silica and aluminum network and so on.

So it becomes some kind of detailed structure.

Normally, one does not need to understand all the different distances which are there, and

It would depend on temperature, it would depend on making production.

But what's important is that we do have with a glass a fixation of the radionuclides inside of the glass structure where it cannot come out.

Except, of course, if the whole glass becomes destroyed or something like this, or if water comes in contact with the glass.

This may dissolve some of this materials, but even that may take a long time.