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> Research on the substance has found, for example, that dumping water on it after it forms actually does stop some fission products from decaying and producing more dangerous isotopes.

What? I bet it doesn't. There's no way cooling will interfere with the half-life of the elements. They probably mean that solidifying the extremities reduces toxic/radiation exposure.




Dude, it's a complicated sludge of radioactive material that is flowing and interacting with itself in complicated ways, not a pure uranium sample on a pedestal.

For instance, cooling it will make the molten metals harden, meaning that there will no material transport. So once some piece of the sludge goes out of criticality, cooling ensures that it will stay sub-critical and decay along a more preferable path.

There is also the possibility that water will do something funky to the chemistry beyond the cooling.


> There's no way cooling will interfere with the half-life of the elements.

Wow, so even at absolute zero, decay happens at the same rate? It kind of makes sense, but it's surprising if you've never thought about it.

Wikipedia seems to confirm it: "A number of experiments have found that decay rates of other modes of artificial and naturally occurring radioisotopes are, to a high degree of precision, unaffected by external conditions such as temperature, pressure, the chemical environment, and electric, magnetic, or gravitational fields." ( https://en.wikipedia.org/wiki/Radioactive_decay )


I have to tell you this is only mostly correct, and there are a few really impressive exceptions. Certain nuclear decay modes, such as electron capture, do depend on the chemical environment of the nucleus.

Beryllium-7 decays purely by electron capture with a half-life of somewhat over 50 days. Differences in chemical environment can alter the half-life by around 0.2%, and high pressures produce somewhat similar changes.

A much more spectacular alteration is if you strip away all the electrons from the very weak beta-emitter rhenium-187 in a particle accelerator, to form a bare nucleus. Neutral rhenium-187 has a half-life of 42 × 10^9 years, the fully ionised rhenium-187 has a half life of just 33 years - a billion fold speed up in decay rate!

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/dec...


> so even at absolute zero, decay happens at the same rate

You'll never get to absolute zero (reality and practicalness aside), because the element radiates it's own heat.


I don't see any reasons why you could not cool radioactive isotopes to essentially zero Kelvin and observe the decay rate. It would probably be hard(er) to do with larger chunks because the decaying nuclei would dump parts of their energy into the sample but if you only use a single atom or maybe tens or hundreds of them and measure the time until the first decay event or between the fist two events you could certainly determine the decay rate close to absolute zero.


> I don't see any reasons why you could not cool radioactive isotopes to essentially zero Kelvin and observe the decay rate

See the GP, this has been tested and proved to have no effect.


Ha, I remember first reading about this when I was discussing with Young Earth creationists. (What a pointless exercise that was …)

Their big point about dating methods was that radioactive decay could be influenced by external factors. No matter how slight that influence, a tiny little bit was enough to disprove all our dating methods.


Water can change things. It might easily combine with the corium to form various hydrates.

Hydrates contain hydrogen, which is a neutron moderator. To the extent that corium's complex decay involves neutrons, changing the neutron energy spectrum (what a moderator does) could change the decay pathways and durations.

Electronic ("normal") and nuclear chemistries can interact.

Edit: Also, water dumped on hot stuff can crack it. Cracks mean that regions of material have changed their geometric relationships, which affect nuclear decay.


Could it have something to do with preventing neutrons from rapidly increasing the rate of decay?

Because we already use water based neutron moderators. https://en.wikipedia.org/wiki/Neutron_moderator


I don't think the Corium is likely to be critical - and if it is, pouring water on it will probably cause an explosion...


Maybe the water absorbs neutrons and slows down the chain reaction?


By absorbing neutrons it reduces neutron-activation of elements in the surrounding environment. The downside is that elements like Cesium are water-soluble so you'll be spreading stuff around a lot more.


This is likely to be from particle capture, in the same way a control rod works.




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