Name: 【地層処分の科学】1-1. 核分裂生成物とは
Uploaded: 2026-01-02T11:32:15.000Z
Duration: 14 min 45 s
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I am professor emerit in EMT Atlantic in France.

And I have worked since about 40 years in the area of nuclear waste and in particular in nuclear waste borosilicate glass, where I made also my PhD in the university or Free University of Berlin.

So my talk is about nuclear waste immobilization in both silicate glass.

Nuclear waste can also is radioactive waste.

And I would just first explain a little bit where this nuclear waste comes from.

So we have a nuclear fission reactor which produces a electricity by using nuclear fuel.

And when put this into a nuclear reactor, the nuclear fission is ongoing.

Here is the reactions which occur and you fabricate fission products.

Here you see, for example, you start with uranium and then by neutrons you split the uranium and you produce two fission products and you produce lots of energy.

And neutrons with very high energy, which you can then use to transform to electricity.

You need to put them in a stable structure, since they are rather dangerous because.

Because they have high radiation products, as you can see here.

Lots of radiation emitted by the fission products.

So nuclear fission produces fission products.

As I said, fission products are dangerous because of their high radioactivity.

Fission products are largely without use.

Long term could be hundreds of thousands of years until they decay to inoffensive levels.

And there is always a risk of dispersion of this fission products somehow.

And so we need to isolate them somehow, forever, whatever means this.

But a very, very long periods of time, hundreds of thousands years, unprecedented somehow in human history to isolate waste or isolate anything or produce anything which would last for such long time period.

Nuclear fission products are not only toxic and in this way dangerous for human being.

There's also decay heat associated to this.

That means the radioactive decay produces heat and also a high dose rate.

You see here in this case, the dose rate as a function of time for about 100 years.

And just to recall that the dose, this is a dose at 1 meter but 1 millisievert.

So it's about here at that level per year is the threshold which human beings are allowed in our society to be exposed to.

Now Here we have 1 millisievert, we have 1 sievert which is thousand times higher.

So these dose rates are extremely much larger than anything the human being can extend, can accept without health problems.

And I think here the lethal dose is about 4 sv.

And so the little dose coming from the nuclear fuel, you get maybe in an hour or so of exposure or even less.

So that means very, very important to isolate this nuclear fuel from human beings and from excess, which is not planned, and

So for doing so, the heat which is produced by the waste, but

also the radioactivity, we need to cool this in the reactor pools for some years.

And depending what to do later on with this nuclear fuel, this can be directly stored.

For example, there's a nuclear fuel rods which you see here from fuel assemblies compared to the human being, which is here at the size just for size comparison, you see that this is rather huge canister or container for dry storage.

And you can have spent nuclear fuel at the bottom there.

And you can see over maybe 4 meters or so of water, you can see down the waste.

Nuclear fuel is essentially uranium dioxide with lots of uranium 235, which is put into the.

The natural isotope composition of uranium is about 0.7% of uranium 235 and 99, 3% of uranium 238.

Now, for being fissile, and the quantity of uranium 235 has been enriched.

And then neutrons could break the uranium and produce fission products.

Some uranium is directly fissile and produce fission products from uranium 235.

But some uranium is also activating the uranium 235.

That means the neutron is taken up by the uranium 235 to produce uranium 236.

But most of the uranium 235, which is about 80%, is just cut by the neutron into two parts.

And these two fission products then are what we call the waste and which we don't.

But this reaction where the neutron breaks the uranium 235 produces lots of energy.

And this can then be converted to electricity.

So this is enriched uranium with uranium 235.

But we have, of course, also uranium 238.

The uranium 238 can then be transformed by neutrons to plutonium 239.

So we have uranium and we have plutonium.

Now, initially we only had uranium, but by the fission we produced fission products, but

we produce also by neutron capture, where the neutron is taken up by the uranium, transforms the uranium into plutonium.

And the plutonium 239 is then again being exposed by neutrons.

You see here, when some of the plutonium is fissile here, it's 72% or 71%.

And some is then capturing another neutron.

And then you go from plutonium 239 to plutonium 40.

So you get a whole series of plutonium isotopes.

And these actinides are also to a certain degree not useful anymore.

So they become also waste and will be disposed of maybe, or they can be reused, used for making another nuclear fuel.

But the fission products are the waste and we need to get rid of.

Either we can dispose the whole thing here, all the products produced by the nuclear reaction.

We can dispose all of this as nuclear waste, the whole thing.

Then we have what we call direct disposal.

After four years or so in the nuclear reactor.

We take it out of the nuclear reactor and we put it inside of.

Alternatively, we have another option that we only take the fission products out.

But for taking the fission products out, we need to do what we call reprocessing.

That means we need to desert, dissolve the entire nuclear fuel, plutonium and the fission products and uranium which is still there, and

dissolve it in nitric acid, very high concentrated nitric acid.

And then once this is done, once it is dissolved, we need a separate chemical separation plant which will separate the different fractions.