Switch on A Desk (the reactor control engineer’s position) for the Unit 4 reactor’s automatic power regulators. The power regulators derive signal from lateral ionization chambers and are used to manage control rod movement under high-power operating conditions. The chain of events leading directly to the accident began with the automatic regulators, which stopped regulating power for some indeterminate reason at 12:30AM on the night of the accident. The operators failed to maintain power with the AR systems, leading to xenon poisoning and the unfortunate conditions for reactor runaway later on.
Switch belonging to the automatic regulator systems in Unit 4, ChNPP