Coping with Nuclear Reactor Leakage: Lessons from Chernobyl and Fukushima

[Bigjoemonger]

On what timescales does concrete lose its integrity?

There's a lot of factors that play into this:
Level of exposure
Type of radiation exposure
Duration of exposure
Quality of concrete
Exposure to the elements
How the concrete is treated to protect it

How it works is when water is added to cement it reacts which causes the material to solidify in a lattice. So it's not hard because it dries out, it's hard because it's hydrated. When concrete is exposed to neutron radiation the neutrons impact with the hydrogen atoms from the water. It breaks the hydrogen bonds and knocks the hydrogen out of the lattice. This dehydrates the concrete which causes the lattice to break apart and the concrete crumbles.

A steel reinforced specially designed concrete containment building 8 feet thick is capable of withstanding the direct impact of a fully loaded passenger airliner and would probably last hundreds of years on it's own.

But a pile of cheap concrete poured directly on top of the elephants foot and exposed to the elements, would probably only last a few decades before degrading. Which is why it's important to build the dome now and keep it contained.

 

[Rive]

... When concrete is exposed to neutron radiation ...

If it is about neutron radiation, then this does not apply for the current Chernobyl.

 

[Bigjoemonger]

If it is about neutron radiation, then this does not apply for the current Chernobyl.

It was an example.

Neutrons impact protons and dislodge them from the lattice, breaking apart the water molecules.
Betas get absorbed, breaking hydrogen bonds, which breaks apart water molecules, same result.
Gammas ionized atoms ripping apart bonds, breaking apart water molecules, same result.

 

[jim hardy]

Concrete is actually a pretty decent reflector of neutrons because of its high water content. Neutrons bounce off

The concrete surrounding my reactor was in fine shape after thirty years of neutron bombardment at perhaps 10¹⁰ nv(that's neutrons / cm² / sec)
I was last down there around 2002 , the year i retired. I presume it's still doing fine for were it not surely i'd have 'heard it through the grapevine'.

@Bigjoemonger - Why do you want to appear sensational ?

When the containment building exploded the melted fuel became exposed to outside air. Which is very bad. A gust of wind or water could carry it and severely contaminate a wider area.

If you remember those days, it was only after other countries complained about fresh fission fragments floating down into their airspace that Russian officals finally admitted something was wrong.

You ought to read up before making wild assertions.
.

 

[Bigjoemonger]

Yes concrete is great at stopping neutrons. But when a neutron "bounces off" what do you think happens to the lattice of the concrete? Think it just stays put? It doesn't, it displaces and interacts with other atoms. One neutron can have an impact on thousands of atoms. Most of it resettles back in it's place but some don't and cause defects. It's ability to reorganize is dependent on the quality of the material. Like I said before, a nice well built reactor vessel or building or what have you could last a really long time before seeing any degradation. Which is why all these plants are getting relicensed way past their original operating timeline because they're still in pretty good shape. But hastily made concrete dumped directly on top of melted nuclear fuel would not last as long.

As for the rest. I don't know what wild assertions you're referring to. And its hard for me to remember those days considering i wasn't born yet when chernobyl happened.

 

[mfb]

Thermal neutrons don't have the energy to induce chemical reactions, for example.

 

[Rive]

And its hard for me to remember those days considering i wasn't born yet when chernobyl happened.

Well. To start with, neutron radiation is significant only in/around working cores.

 

[nikkkom]

Yes concrete is great at stopping neutrons. But when a neutron "bounces off" what do you think happens to the lattice of the concrete? Think it just stays put? It doesn't, it displaces and interacts with other atoms. One neutron can have an impact on thousands of atoms. Most of it resettles back in it's place but some don't and cause defects. It's ability to reorganize is dependent on the quality of the material. Like I said before, a nice well built reactor vessel or building or what have you could last a really long time before seeing any degradation. Which is why all these plants are getting relicensed way past their original operating timeline because they're still in pretty good shape. But hastily made concrete dumped directly on top of melted nuclear fuel would not last as long.

Again, melted nuclear fuel does not emit significant amounts of neutrons.
Betas affect only a few first millimeters of concrete.
Gammas can not dislodge atoms, they only knock out electrons. Depending on material's chemical properties, this may be ineffective at destroying its structure: for example, metal objects will not be damaged by it at all. I don't know about concrete.

I am not convinced that Chernobyl's concrete is seriously affected by radiation.

 

[Rive]

I am not convinced that Chernobyl's concrete is seriously affected by radiation.

It is not.

It is affected by the fact that it was a more heroic than thorough build due the radiation (way back), but that cannot be measured by any dosimeter.

 

[jim hardy]

I am not convinced that Chernobyl's concrete is seriously affected by radiation.

I agree.

Actually concrete is affected more quickly by high temperature than by radiation. That's how you make cement, cook limestone to dehydrate it.

For that reason our reactor shield had coils embedded for cooling water .

What radiation damage there is drops off quickly with distance because of self shielding.