Design of NPP Steam Generator Water-level Alternate Measuring System Based on PLC

Steam Generator (short for SG) water-level controlling system is the most important controlling system in the second loop of PWR Nuclear Power Plant (short for NPP). If this system falls in abnormal operation, the steam generator water-level deviate from the set value. When the water level exceeds the specified limits, it will result in reactor shutdown, and affect the economy of the NPP and rank of WANO. The SG water level controlling system of Qinshan No.1 NPP puts into use in 1994. Due to the limitation of technical level at that time, microcontroller runs at a slow speed and the memory capacity is small. Transient process and bulk data processing will cause the system collapse. In service, proportional integral regulator output saturation occasionally, which cause level out of controlling. Worse still, manufacturer is no longer producing such kind of hardware and technical supports are unavailable at the same time. In order to supply a reliable backup water level measurement system for operator, when the main Steam Generator water-level control system fails, we design and produce an alternate level measurement system based on Siemens PLC, S7-315.