United Kingdom Sizewell B WISCO-2 Data Processing and Control System Replacement Project. Annex 1

The Sizewell B NPP in the United Kingdom is a four loop PWR owned and operated by Électricité de France (EDF). It was constructed in the early 1990s, entering commercial operation in 1995. The data processing and control system, known as the Westinghouse Integrated System for Centralised Operation (WISCO) was supplied by Westinghouse Electric Corporation (WEC) and has been in continuous operation since the mid‑1990s. The vast majority of closed loop and sequence controls are provided by WISCO, together with manual actuation of plant, data acquisition, alarm management and nuclear safety calculations to support plant operations. WISCO comprises three separate subsystems: (1) the process control system (PCS); (2) the distributed computer system (DCS); and (3) the high integrity control system (HICS). The PCS and HICS execute control algorithms and provide the direct interfaces to plant and control room devices, whereas the DCS provides graphical displays, data processing, alarm management and logging functions. The PCS/DCS was based on the WEC WDPF‑II product line, whereas the HICS was based on the WEC Eagle‑21 product line. All systems have performed reliably since original commissioning and have been in continuous operation 24 × 7 with less than 4 h down time in the last 25 years. However, all systems in WISCO have been obsolete for many years. Therefore, the decision was taken in 2012 to modernize the PCS/DCS subsystems of WISCO, but retain HICS for the foreseeable future. This decision would also involve replacement of the off‑line maintenance and test systems for the PCS/DCS as well as a significant upgrade to the full scope training simulator to accurately represent the behaviour of the new system. The partial modernization project, hereafter referred to as WISCO‑2, is discussed in this annex. It describes the key decisions for the replacement project, the challenges and how they were solved, highlighting lessons, both positive and negative, which other similar projects would need to consider.