"These are not nuclear explosions. These are what we call non-critical explosions."
FYI he's referring to nuclear "criticality," e.g. testing the non-nuclear explosives placed around core. To simplify, the yellow stuff here:

...That is totally fine. It's a good idea.
It's also a great escape from what Trump said. If you're energy secretary under Trump, this is exactly how you get out of this (and just hope Trump doesn't notice).