Computer-based Safety Systems — The Elements of an Acceptable Safety Case

Abstract

The following is a record of the presentation given by D M Hunns to the Conference. The views summarised here are the author’s own and should not be regarded automatically as representing those of his employer.

The presentation concentrated on the safety case issues associated with the application of computer technology to the provision of a protection system for a nuclear power station — the computer-based Primary Protection System operating at UK’s Sizewell B station (Pressurised Water Reactor) was cited as a key example.

It was noted that UK’s nuclear regulatory regime stipulates that the adequate safety of a plant must be justified by a formally documented “safety case”. A brief outline was given of the process by which the Nuclear Safety Division (within UK’s Health and Safety Executive) normally assesses such a case, and reaches a view on the acceptability of the associated plant.

This was followed by a consideration of some of the pros and cons associated with the use of computer technology in a reactor safety system role. The challenge posed to the making of a convincing safety demonstration was specifically identified. A brief description was given of the means by which this problem was overcome for Sizewell B.

Finally, views were offered on the ways by which the safety demonstrations for such systems might develop in the future.