Document: NUREG-0800
Document ID: 6209b3e7-917d-48d2-a299-4d1230aa5b51
Document Type: srp
Title: Revision 5 - March 2007
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0705/ML070550070.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
onal delays interposed between the sensor and the actuator. An allocation of time delays to elements of the system and software architecture should be available. In initial design phases (e.g., at the point of design certification application), an estimated allocation of time delays to elements of the proposed architecture should be available. Subsequent detailed design and implementation should develop refined timing allocations down to unit levels in the software architecture. A design should be feasible with currently known methods and representative equipment. Design timing feasibility may be demonstrated by allocating a timing budget to components of the system architecture so that the entire system meets its timing requirements. See NUREG/CR-6083, Sections 2.2, 2.3.1, and 2.3.2, and NUREG/CR-6082. The timing budget should include internal and external communication delays, with adequate margins. Any non-deterministic delays should be noted and a basis provided that such delays are not part of any safety functions, nor can the delays impede any protective action. Software architectural timing requirements should be addressed in a software architectural description as described in SRP BTP 7-14. Databases, disk drives, printers, or other equipment or architectural elements subject to halting or failure should not be able to impede protective system action. Design Commitments Design basis documents should describe system timing goals. Timing requirements should be satisfied by design commitments. A design should consider data rates, data bandwidths, and data precision requirements for normal and off-normal operation, including the impact of environmental extremes. There should be sufficient excess capacity margins to accommodate likely future increases in demands or software or hardware changes to equipment. Design basis documents should identify design practices that the applicant/licensee will use to avoid timing problems. Risky design practices such as