The problem began just after lunch on Feb. 8, when a group of technicians tested a computer called the “Rodworth Minimizer.” The unit, which operates when the reactor is at low power, analyzes the position of “control rods” in the core and tells engineers which ones can—and cannot—be removed to balance power distribution.

To simulate Jan. 1, the technicians had intended to connect the Rodworth to another computer that would serve as a clock. But instead of connecting the unit to the external clock, a programmer inadvertently reset the date on the backup and primary operations monitoring systems, which are not yet Y2K compliant.

As soon as the date was reset, the screens in the control room went blank.

After discussion the team decided to restore the operations system in a piecemeal fashion, testing each part as they went along. They didn’t want to bring up the system only to have it crash again.

The whole task took seven hours.