All of this is made up nonsense. Only 14 radioactive fission product isotopes end up in the final waste form, and they are in an inert oxide form. Their decay chains are short and hardly change the chemistry, if anything, it becomes more stable. They also don't produce gasses, much less radioactive ones.

The only kernel of truth is that __if__ you throw out fuel instead of waste, then you get a heat problem over the long term and the container is irradiated by alpha particles. It won't melt, but it might corrode. But why would you throw away fuel?