The first CANDU* reactor (Pickering A, Unit 1), began commercial operation in 1971 at Ontario Hydro's Pickering A reactor site, just east of Toronto. In 1973, the Pickering A Nuclear Generating Station equipped with four CANDU reactors, produced more electricity than any nuclear power station in the world at that time.

Through cooperation with CANDU designer Atomic Energy of Canada Ltd. (AECL), or directly with power generation utilities, L-3 MAPPS has been supplying CANDU plant computer systems - known as Digital Control Computer (DCC) systems - for nuclear power plants since 1970. DCC systems are used to monitor and control all the major reactor and power plant functions. In response to demand, L-3 MAPPS has continued to upgrade the technology over the last three decades.

A typical system consists of two DCCs. DCC X and DCC Y are redundant
on-line controllers, which control the nuclear reactor. Each controller uses
a computer with purpose-built process I/O interface and peripherals housed in cabinets, and utilize additional freestanding peripherals such as keyboards, printers and monitors. A contact scanner is used to scan relay contacts, limit switches, or other similar types of contacts. The scanner is connected to both DCC X and DCC Y, but communicates with only the annunciating DCC.

L-3 MAPPS has sold 29 DCC systems for nuclear power plants in Argentina, Canada, China, Italy, Korea and Romania.

* CANDU is an acronym for CANada Deuterium Uranium, designed by AECL. The CANDU system is a unique design that uses deuterium oxide (heavy water) as the moderator and coolant, and natural uranium as fuel.