Xenon, etc.

Last month, a six-times normal Xenon concentration in the air was monitored in South Korea. That spurred looking for evidence of a nuclear test (none found) or some kind of reactor accident. Nothing was stated, but North Korea did mention a breakthrough in fusion energy of some kind. Of course, the Xenon could have come from China or even the former USSR.

That is why right now this article is interesting - it mentions research programs here that would essentially release Xenon to atmosphere.