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In my post, I said the entire problem was “thermal”, that is, at high temperatures chemical reactions occur. Are you disagreeing?

This notion about dissociation of water into H2 and O2 needs an ocean of better understanding. Start with, it is wrong.**

You must understand that in a reactor volume the water, H2O, is not isolated; every molecule can interact with the fuel rods, that is, the zirconium atoms in the zirconium alloy called Zircaloy. This is a surface chemistry effect, and there the Zr atoms react with water to create ZrO2 and H. The hydrogen forms bubbles, which rise to the top and collect there.

Indeed, we want every water molecule to hit the surface, get hot, and move away, carrying heat away. That is what heat transfer means.

But you can’t stop the little devils from having a relationship, namely oxygen atoms in water preferring to marry zirconium atoms coventently.

There is no “dissociation” other than a chemical reaction that results in two new compounds, one of which is hydrogen gas, from the H2O. There are also interactions with hot H2O molecules with the containment vessel surface.

**It is true that at a high enough temperature, which depends on the pressure, that water molecules of H2O break down into H2 and O2 molecules. Roughly, this is about 1400 C. But you can look up all the enthalpy, free energy, bond energy factors as you wish.

Consider that you have a flask of hot water vapor—steam—at this high temperature where the “dissociation” occurs. You cannot separate the oxygen molecules from the hydrogen molecules. As soon as the flask cools, they recombine to make just water vapor. NO EXPLOSION—because the thermal energy originally needed to dissociate the water molecule is returned to the kinetic energy (translational and rotational) of the molecules in a hot gas.

So, in such a closed system you have caused dissociation-—but it has no effect. The original water returns to water.

The point is that the water in a reactor is not isolated-—the water molecules react with the surfaces they encounter. The reaction kinetics depend on the temperature. I described a tiny bit of what happens at the Zircaloy surface. Do you disagree?

The water molecules also interact with the containment walls—”stainless steel”, that is, a mixture of iron, cobalt, chromium, nickel, et al. with a pinch of vanadium and manganese.

It is not thermal dissociation of water-—it is chemical reactions. It is chemical reactions that carry away the oxygen atoms in water and leave hydrogen to bubble.

It is this hydrogen, when it mixes with air-—80% nitrogen, 20% oxygen—that leads to fires and sometimes explosions.

Do you disagree?