The rapid is kinda redundant, because if it's unscheduled, it's going to be caused by a spontaneous release of energy stored onboard (as opposed to a scheduled, planned disassembly, where the energy is applied by external workers). Most spontaneous releases of enough energy to disassemble a launcher will be rapid.

Of course, RUD is already established in the space industry's jargon.

RUD = it turned into "rudere" [1]

[1] https://en.wiktionary.org/wiki/rudere#Italian