Office for Nuclear Regulation
An agency of HSE

Computer based safety systems - WENRA reference levels

T/AST/046 App 5

A5.1  There is one section of the WENRA Reactor Safety Reference Levels (Ref.16) that is directly relevant to the use of computer based safety systems (i.e. Appendix E – Issue: Design Basis Envelope for Existing Reactors, clause 10.10). The software aspects of clause 10.10 are implemented through application of SAP ESS.27 and the guidance shown in this TAG (other SAPs address hardware aspects). Clause 10.10 from Ref.16 (January 2008 revision) is shown below and references into the main body of this TAG are provided in Bold text.

  • 10.10 Computer based systems used in a protection system, shall fulfil the following requirements:
  • the highest quality of and best practices for hardware and software shall be used; [4.3]
  • the whole development process, including control, testing and commissioning of design changes, shall be systematically documented and reviewed; [4.3]
  • in order to confirm confidence in the reliability of the computer based systems, an assessment of the computer based system by expert personnel independent of the designers and suppliers shall be undertaken; [4.4] and
  • where the necessary integrity of the system cannot be demonstrated with a high level of confidence, a diverse means of ensuring fulfilment of the protection functions shall be provided. [4.1.1, 4.2.1 and Appendix 4]

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Updated 06.01.12