Document: NUREG-0800
Document ID: 4cca74ec-66e0-4765-9c61-cf547e17c308
Document Type: srp
Title: of the plant safety analysis report (SAR).  Although the NRC did not endorse the annexes of
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1601/ML16019A114.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7.6
CFR Part: 
CFR Title: 

Content:
uld not receive input or influence from any nonsafety system while the safety system is online and performing that safety function. The following provides some of the possible design approaches that a reviewer may encounter for data communications. It is neither exhaustive nor limiting in the possible approaches. If the reviewer is not sufficiently familiar with the communications systems and methods being used, the reviewer should seek the assistance of other NRC personnel or the supervisor for the appropriate review strategy to determine that the communications cannot interfere with the safety function. • A communications system that broadcasts data from the safety system to the nonsafety system without the use of handshaking and acknowledgment signals would satisfy these requirements. Appendix 7.1-D-19 Revision 1 - August 2016 • If the communications system allows two way communications between the safety and nonsafety systems, the determination may require a more detailed examination of the communications method, including memory allocation methods, communications protocols and message-formatting methodology. One possibility may be to determine that the communications method is deterministic, that is, the same information is transmitted in the same way to the safety system, and is then used by the safety system in the same manner. This could be done by having the nonsafety system write data to a specific location in shared memory, and the safety system would read that data. The safety system should understand the data and be able to process that data for all possible circumstances. The data in that memory location should be the latest written value of the data. Therefore, safety systems should have provisions for out-of- date data, garbled data, and communication link failure. This is one, but not the only possible method of deterministic communications. The objective in the review is to determine that the applicant or licensee has satisfactorily