I am a chemist.
First, it's thermal production of H2 and O2 not radiological.
2 molecules of water produce one molecule of O2 and 2 molecules of H2
a similar reaction takes 2H2O +Zr -> ZrO2 + 2H2
The purely thermal reaction produces H2 and O2 in equal proportions. This reaction is likely...
From the same article
It's worth reading the whole article. Combined with the thermal production of hydrogen and oxygen from steam, this explains why they wanted to add N2 gas into the reactors.
For those wondering where the oxygen can come from. Water can also be split into hydrogen and oxygen by temperature alone. It occurs above 2500 C and can be catalyzed by metal oxides which lower the temperature required. When the rods in the core are not covered with water, they can reach these...