A Prime Base Survivor

[cosmicfish]

Look at this from a different viewpoint: It is essential to the story that everyone in PB is killed but that the facility itself survives essentially intact. So starting from a blank slate, how do we kill PB?

A biological agent would only work if the defensive measure was to preventively place everyone possible into cryosleep early on, and even then it would be a remarkable stroke of bad luck to keep awake only those who were susceptible. A chemical or radiological agent could be much more effective, but how does that get into a facility designed specifically to keep such things out?

It seems impossible to me that PB could fall physically intact but with no survivors without either some element of internal betrayal or some level of Krell superscience. Does one of those sound particularly plausible, or is there some solution I am not seeing?