Inside SKALA: The Computer System That Controlled Chernobyl’s Reactor
Running a nuclear power plant, even with the automation of a 1980s Soviet RBMK reactor, is a complex undertaking. Recent efforts to recreate a functional RBMK control room, mirroring that of the Chornobyl Nuclear Power Plant, have focused on the SKALA system – the plant’s industrial control system.1
The SKALA System: A 1970s Design
SKALA, designed in the 1970s, comprised multiple V-3M processor racks, or ‘frames,’ each equipped with 20k 24-bit words of RAM. While less powerful than a PDP-11, SKALA’s primary function was to collect and process sensor data in real-time.1 The DREG program, output from SKALA, provided the final messages from the #4 reactor before the accident.
Modernization Efforts in the 1990s: The DIIS System
Despite its limitations, SKALA remained in apply after the 1986 disaster. During the 1990s, as the Chornobyl Nuclear Power Plant continued operating with its remaining three RBMK reactors, engineers recognized the necessitate for modernization. Rather than replacing SKALA entirely, they developed an auxiliary information-measurement system called DIIS.3
DIIS bridged into SKALA via a Ukrainian-made SM-1210 minicomputer, which was connected to an 80386 PC and an ARCnet hub.3 This upgrade enabled the running of modeling algorithms for the reactor core based on real-time measurements, without needing to transmit data to Moscow. Reactor parameters could then be visualized and adjusted using the same PRIZMA program and magnetic tapes previously used with the SKALA system.
A Hybrid System
The resulting system was a unique combination of 1970s Soviet mainframe design, 1980s Ukrainian mainframe design, and 1990s Intel computing power.1 This hybrid approach proved effective, allowing the Chornobyl NPP to operate until the early 2000s – Unit 2 was active until 1991, Unit 1 until 1996, and Unit 3 was shut down in 2000.1
The success of this modernization effort is a testament to the ingenuity of the engineers who adapted and integrated these disparate technologies.
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