Document: NUREG-0800
Document ID: 96afb1d6-6ce9-41e4-b4ec-1fc7747bc0b2
Document Type: srp
Title: Revision 8 – January 2021
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML2033/ML20339A647.pdf
Revision Date: 2023-05
Chapter: 7
Section ID: 7
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ed operational occurrence (AOO), a postulated accident (PA), or normal operations, while spurious operations are postulated as an initiating event. In accordance with Commission direction in the staff requirements memorandum (SRM) on SECY-93-087, “SECY-93-087—Policy, Technical, and Licensing Issues Pertaining to 1 IEEE 100, The Authoritative Dictionary of IEEE Standards Terms, defines “firmware” as the combination of a hardware device and computer instructions and data that reside as read-only software on that device. 2 Where this BTP refers to “CCF,” it is always referring to CCF due to a latent design defect in active hardware components, software, or software-based logic. 3 CCFs due to latent design defects in DI&C SSCs are similar to but distinguishable from cascading failures due to single random failures. Single failures must be addressed by meeting the criteria described in 10 CFR 50.55a(h) (i.e., they are required to address safety design criteria in IEEE Std 279-1971 or IEEE Std 603-1991). Because such failures are likely to occur during the life of the plant, the design basis for the plant needs to consider the analysis of the possible effects (consequences) of such failures. BTP 7-19-3 Revision 8 – January 2021 Evolutionary and Advanced Light-Water Reactor (ALWR) Designs,” dated July 21, 1993, the staff considers CCF in DI&C systems to be a beyond-design-basis event. The likelihood of occurrence of these failures cannot be predicted through traditional design analysis methods, but their effects and consequences can be addressed through other methods, such as best estimate methods. DI&C systems can integrate design functions that were previously located in separate and dedicated analog systems. For example, formerly discrete systems (e.g., the reactor trip system (RTS) and the engineered safety feature actuation system (ESFAS)) can be combined into a single DI&C protection system. Also, DI&C systems can share resources, such as