Document: NUREG-0800
Document ID: fea61ff0-f344-4101-adfb-590e3d9dfafe
Document Type: srp
Title: Draft Revision 6 – August 2015
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1515/ML15159A946.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
ow. B.3.3.3.1 Functional Characteristics of SDS 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 means that all calculations are 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 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 means that the detailed software design is such that single failures of individual elements will not cause safety system failure. Robustness means that the design is 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 BTP 7.14-55 Draft Revision 6 - August 2015 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 means that the detailed design introduces no new safety hazards into the safety system. Security means that unauthorized changes are prevented, detected, or mitigated as appropriate per RG 1.152. Timing means that the time