In 1983, on top of the myriad drawbacks of the reactor that had emerged since it went into operation, the reactor designers learned of one more: a curious design fault in the rods of the AZ-5 emergency protection system. The first conclusive evidence appeared at the end of the year, during the physical start-up of two of the newest RBMK reactors to be added to the Soviet grid: Unit One of the Ignalina nuclear power plant in Lithuania, and Unit Four in Chernobyl, the most advanced of the RBMK-1000 line.
