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:
e elements in the architecture. A two-way trace should exist between the architectural elements and the detailed design elements. There should be a forward trace from each architectural element to the specific inspections, analyses, or tests that will be used to confirm that the element has been correctly designed. Verifiability requires that it be possible to construct specific analyses, reviews, and tests to verify that the architecture satisfies the software requirements. c. Design Activities & Software Design Specification An SDS should be produced. The SDS should include all of the functional and software development process characteristics listed below. Functional Characteristics For each of the functional characteristics, the requirements imposed on the software for that characteristic should be satisfied by the software design. Product functional characteristics addressed by the SDS should include accuracy, reliability, robustness, safety, security, and timing. Accuracy requires that all calculations be specified in such a way that the accuracy requirements for the calculations will be satisfied. In particular, floating point arithmetic should be avoided; if that is not possible, special care must be taken to maintain the accuracy of the calculations. The design should specify the method for determining that the values of input variables are within the proper range, the Appendix 7-A Rev. 4 — June 1997 BTP HICB-14-33 method by which the software will detect that the values of input variables are not within their proper range, and the actions to be taken in the latter case. All calculations should be analyzed for convergence, round-off error, precision, and accuracy as appropriate. Reliability requires that the detailed software design be such that single failures 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