Document: NUREG-0800
Document ID: fe8ec6c2-e960-404c-854f-55c77bde1672
Document Type: srp
Title: NUREG-0800
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML2400/ML24005A077.pdf
Revision Date: 2024-05
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
effects: (1) they can cause a loss of the capability to perform a safety function or can initiate a plant transient, or (2) they can initiate the operation of a function without a valid demand or can cause an erroneous (i.e., spurious) system action. The latter is typically referred to as “spurious operation” or “spurious actuation.” CCFs with a loss of safety function are postulated concurrent with an anticipated operational occurrence (AOO), a PA, or normal operations, while spurious operations are postulated as an initiating event. In accordance with Commission direction in the staff requirements memorandum (SRM), dated July 21, 1993, on SECY-93-087, “Policy, Technical, and Licensing Issues Pertaining to Evolutionary and Advanced Light-Water Reactor (ALWR) Designs,” dated April 2, 1993, the NRC staff considers CCFs in DI&C systems to be beyond design-basis events.3 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 system modifications can interconnect design functions that were previously located in separate or dedicated equipment. These modifications could therefore introduce new failure mechanisms. Also, DI&C systems can share resources, such as communications, networks, controllers, power supplies, or multifunction display and control stations. The potential for 1 In this BTP, the term “CCF” always refers to CCF due to a latent design defect in active hardware components, software, or software-based logic. 2 CCFs due to latent design defects in DI&C structures, systems, and components (SSCs) are similar to but distinguishable from cascading failures due to single random failures. Single failures must be addressed by meeting the principal design criteria of the facility or the criteria described in 10 CFR 50.55a(h) (i.e., the safety design criteria in Institute of Electrical