Document: NUREG-0800
Document ID: c90016c6-e03f-4224-8ff3-87a6f7d3ca42
Document Type: srp
Title: Appendix 7-A
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0525/ML052500547.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
es of individual elements will not cause safety system failure. Robustness requires that the design be such that the software will operate correctly in the presence of unexpected, incorrect, anomalous and improper (1) input, (2) hardware behavior, or (3) software behavior. In particular, the software should not fail, and should not provide incorrect outputs, in the presence of these conditions. Attention should be paid to those values of input variables that are physically possible to the device, even if logically impossible in the application (to account for sensor errors, communication line noise, and similar concerns). Safety requires that the detailed design introduce no new safety hazards into the safety system. Security requires that unauthorized changes be prevented, detected, or mitigated as appropriate. Timing requires that the time delay between stimulus and response be deterministic. BTP HICB-21 provides additional guidance on real-time performance. Software Development Process Characteristics The SDS should exhibit each of the following software development process characteristics: completeness, consistency, correctness, style, traceability, and verifiability. Completeness requires that the detailed design specify the actions of each software unit for the entire domain of each input variable (for example, the complete span of instrument inputs or clock/calendar time). The design should be sufficiently complete to permit implementation to take place. Actions should be specified for all situations anticipated in the SRS. Equipment, human, hardware, and software interfaces should be correctly and fully specified. Equations, algorithms, and control logic should be correctly and fully specified. Consistency requires that the detailed design be consistent with the architectural design, and that the detailed design elements be mutually consistent. Design elements should be consistent with documented descriptions and known properties of the operational