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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Content:
nd 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. BTP 7-21-8 Draft Revision 6 – August 2015 Design basis documents should identify design practices that the applicant/licensee will use to avoid timing problems. Risky design practices such as non-deterministic data communications, non-deterministic computation, use of interrupts, multitasking, dynamic scheduling, and event- driven design should be avoided. When such practices are allowed, the applicant or licensee should describe methods for control of the associated risk. NUREG/CR-6082 and NUREG/CR-6083 describes risky design practices in more detail. Performance Verification The means proposed, or used, for verifying a system's timing should be consistent with the design. Testing and/or analytic justification should show that the system meets limiting response times for a reasonable, randomly selected subset of system loads, conditions, and design basis events. The subset should include some limiting load conditions and be chosen by persons independent of the persons who designed the system. Both analytical and test techniques of timing analysis have drawbacks. It is difficult to demonstrate