Before revision: Instead, a massive power excursion during a mishandled test caused the catastrophic failure of the reactor vessel and a near-total loss of coolant supply.
After revision: (exacerbated by the high and positive void coefficient of the RBMK as it was designed and used at the time)Instead, a massive power excursion during a mishandled test caused the catastrophic failure of the reactor vessel and a near-total loss of coolant supply.