Document: NUREG-0800
Document ID: 6acfc377-3e1c-4cb9-b2d1-500f564d2f4b
Document Type: srp
Title: Draft Revision 6 – August 2015
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1515/ML15159B011.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
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CFR Title: 

Content:
Setpoint analyses and limiting response times should also be shown to be consistent. The reviewer should verify that limiting response times are acceptable to the organizations responsible for reactor systems, electrical systems, and plant systems before accepting the limiting response times as a basis for timing requirements. Digital Computer Timing Requirements Digital computer timing should be shown to be consistent with the limiting response times and characteristics of the computer hardware, software, and data communications systems. Computer system timing requirements that should be addressed in software requirements specifications are described in SRP BTP 7-14. Architecture The level of detail in the architectural description should be sufficient that the Staff can determine the number of message delays and computational 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