Software maintenance for I&C systems - Important to safety

I&C (instrumentation and control) systems must meet the most stringent deterministic and probabilistic safety criteria for safe operation of nuclear power plants. To ensure that these requirements are met throughout the operating life of a plant, reliability of the I&C systems must be guaranteed over their full period of operation. In digital I&C systems, this includes the requirement of continuous software maintenance to ensure that the software quality proven and demonstrated in the licensing phase and the permit, respectively, continues to meet requirements. In the case of software modifications, e.g. as a result of process or plant modifications, this implies quality assurance of these modifications, and the demonstration of functionality and safety also in changes of hardware as a consequence of the progress in development of digital systems. In 2001, the TELEPERM XS system installed at the Unterweser Nuclear Power Station, including its software, was greatly expanded and modified. That effort was completed successfully within the envisaged framework, and both the hardware and the software employed meet the required standards of quality and offer sufficient robustness of the system. The software is being developed further with the objective of having the next version licensed in late 2002.