Document: NRC Regulatory Guide
Document ID: bcbe26a0-004f-4616-b7f4-b32b2bfe4909
Document Type: regulatory_guide
Title: Setpoints for Safety-Related Instrumentation (Rev. 4)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2005/ML20055G823.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.105
CFR Part: 
CFR Title: 

Content:
and not direction, and depicts uncertainty relationships that do not represent any particular direction, combination, or relationship of uncertainty groupings for the development of a trip setpoint or allowable value. This figure has been updated from the 1994 and 2006 revisions of the standard to illustrate relationships among the limiting and nominal trip setpoints, the analytical limit, and the safety limit. It also illustrates the relationship among the nominal setpoint and the AFT and ALT limits. The revised figure no longer depicts a relationship between the nominal setpoint and the technical specification allowable value, and expanded content within Section 4.6 (Performance Acceptance Criteria) of ANSI/ISA 67.04.01-2018 addresses the concerns in RIS 2006-17. DG-1363, Page 8 2.2.6 Graded Approach Based on Safety Significance Since 1994, Section 4 of ANSI/ISA S67.04.01 has stated that the safety significance of various types of setpoints for safety-related instrumentation may differ and a less rigorous setpoint determination method may be applied for certain functional units and LCOs. The NRC staff has not identified a specific position on the appropriate technical methodology to be used when establishing setpoints for nonlimiting safety system setting-related instrument channels. 2.2.7 Measurement and Test Equipment Uncertainties Section 4.4 of ANSI/ISA 67.04.01-2018 provides for the accounting of measurement and test equipment uncertainties but does not specifically identify acceptance criteria. Additional information for determining measurement and test equipment uncertainty may be found in the ISA recommended practice document ISA-RP67.04.02-2010, “Methodologies for the Determination of Setpoints for Nuclear Safety-Related Instrumentation” (Ref. 11). The NRC staff does not endorse any version of ISA-RP67.04.02, however, the staff believes those versions contain useful information. 2.2.8 ISA Recommended Practice ISA-RP67.04.02 Section 4.4 of ANSI/ISA