When you place something radioactive in a portable storage block such as a steel crate, it becomes radioactive and will continue to be like that until the radioactive item(s) are removed from it; however, this does not apply to non-NTM portable storage blocks which makes radioactive items essentially harmless until placed back into your inventory or a crate.

This makes crates sort of obsolete by the time you get your hands on nuclear tech since you can just pop radioactive stuff into a non-NTM portable storage block, break it, and take it to where you want it to be in, all without the fear of getting severely contaminated with radiation. If it's even possible, this radiation blocking method could be patched by making it so the game treats such items from certain mods (e.g. EFR's Shulker Box and backpacks in Eydamos' mod Backpacks) as if they were NTM crates.