One theory is that the "sea peoples" were not any specific group but rather refugees from various city-states that were smaller and had fewer resources and so collapsed earlier. These people likely traveled to other places that had not yet collapsed, where they were scapegoated by the local leaders as the source of socioeconomic problems, just as refugees and migrants are today - which explains historical records that pin blame on the "sea peoples".
The Bronze Age collapse was probably caused by systemic issues, not by the actions of any particular group, but it was easier to blame refugees than actually study and deal with the real problems.
The Fall if Civilizations podcast has a great episode on this:
I was wondering how radioactive the resulting material would be. Twenty years is totally viable for a power plant. Reactors in the US have been storing nuclear waste on site for a lot longer than that.