Assessing software based safety systems against the requirements and recommendations of IEC 880 (1986)

This paper examines the process of assessing software-based systems against the IEC 880 (1986) standard "Software for Computers in the Safety Systems of Nuclear Power Stations". An overview description of IEC 880 is provided and the relationship between the requirements in the main body of the standard and the guidance provided in the appendices is discussed. Some fundamental issues to be considered when performing an assessment are highlighted. In particular, the analysis of the development lifecycle, including consideration of issues such as the multiple iterations of development phases and the use of pre-existing system components, is discussed. The various types of software/data which are present in a typical system are described and the applicability of the standard to each is reviewed. In conclusion, the author recognises the broad scope and relevance of IEC 880, but also highlights the practical problems encountered when attempting to gauge the 'compliance' of a system. The author provides some recommendations for assessors.