CANDU Plant Control Systems

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 a purpose-built process input/output (I/O) system and peripherals housed in cabinets, and use 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.

The DCC system architecture is centered on two technologies – the central processing unit (CPU) and the I/O system. The CPU technology has evolved from the initial Varian 70 family of microcomputers to the current Second Source Computers Inc. (SSCI) CPU, first the SSCI-125 generation and now the SSCI-890. The I/O system is based on the Datapath 50 data acquisition and the control system technology is designed and manufactured to monitor and control CANDU reactor units. Every consideration has been taken into account throughout all stages of design and construction to ensure that the system operates with maximum efficiency and reliability.

The SSCI-890 computer features a single board CPU, a cache board and 2MB memory modules. The CPU and memory communicate over a special system connector plane that eliminates inter-connect cables. The SSCI-890 CPU includes mapped main memory. A map on the CPU board can perform efficient memory management for up to sixteen million bytes of main memory with full memory protection. The memory modules combine 2MB of metal-oxide semiconductor (MOS) memory with error-correcting code (ECC) on a single plug-in module.

Along with the SSCI-based CPU architecture, we have supplied and supported the PDP-11/70 DCC CPU architecture. This implementation, in service for more than fifteen years at Ontario Power Generation’s Darlington Nuclear Generating Station, was the subject of an innovative L3Harris replacement through a t, form, and function hardware emulation.

In addition to the continuous enhancement of CPU performance of the DCCs, we have updated and re-designed several peripheral equipment and interface controllers related to the data storage, printing, and the data acquisition interface with PCs. The new Bulk Storage Memory Unit increases the total memory size to 128MB and provides for an extended area of housing software applications and historical data storage buffers. The new technology of network printing – using fast laser printers – required an adaptation of printer controllers for alarm messaging and hardcopy functions.

Committed to continuous improvement of the DCC design, we have successfully emulated the functionality of the Main Control Room Display System with the use of our VME-based technology. This emulation solution has resulted in a complete replacement of Ramtek equipment while maintaining the same DCC software developed by utilities and used on the original display system hardware.

The same VME-based technology was the baseline of replacing the Contact Scanner equipment and presently this implementation is in operation in both units at the Qinshan Phase III Nuclear Power Project (Zhejiang, China) and on Unit 2 at the Cernavoda Nuclear Power Plant (Cernavoda, Romania).

Our goal is to ensure that COG and CANDU plant operators have a solid, reliable supplier on whom they can rely for their maintenance and support services. L3Harris has been supporting the DCC for 50 years and is firmly committed to not only continue, but to enhance our support for the product line for the next 50 years.