Instead, they produced a separate appendix, based upon their own independent investigation. This opinion suggested that—whatever the operators’ mistakes—Reactor Number Four could never have exploded were it not for the profound defects in its design, including the positive void coefficient and the faulty control rods that made reactivity increase rather than decrease. Their detailed technical analysis raised the possibility that pressing the AZ-5 button, instead of safely shutting down the reactor, as it was supposed to do, may have caused the explosion.
