Document: NUREG-0800
Document ID: 5989239b-cda8-4832-8a1c-ff0c221fca34
Document Type: srp
Title: Draft Revision 6 – August 2015
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1515/ML15159A799.pdf
Revision Date: 2023-06
Chapter: 7
Section ID: 7
CFR Part: 
CFR Title: 

Content:
cription of assumptions in accordance with ISA-S67.04-1994, Part I, should include the environmental allowances (temperature, pressure, humidity, radiation, vibration, seismic, and electrical) for the instruments. Analysis Supporting Establishment of Setpoints and Instrumentation Tolerances The applicant or licensee should document the bases and the calculations of measurement uncertainties. The methods by which setpoints are calculated should conform to the guidance in RG 1.105. Statistical Guidelines for Instrument Uncertainty In the review of uncertainties in determining a trip setpoint and its allowable values, the NRC staff typically uses 95/95 tolerance limits as an acceptable criterion, i.e., a 95 percent probability that the constructed limits contain 95 percent of the population of interest for the surveillance interval selected. Guidelines for Graded Approach ISA-S67.04, Part I, Section 4 states that the safety significance of various types of setpoints important to safety may differ, and thus a less rigorous setpoint determination method for certain functional units and limiting conditions of operation may be applied. The use of a graded approach allows a less rigorous setpoint determination method based on the safety significance of the instrument function. However, the grading technique chosen by the applicant or licensee should be consistent with the standard and should consider and bound all known applicable uncertainties regardless of setpoint application. Additionally, the application of the standard using a graded approach is also appropriate for nonsafety system instrumentation maintaining design limits in the technical specifications. Basis for Instrument Calibration Intervals The applicant or licensee should evaluate the effects of extended calibration intervals on instrument uncertainties, equipment qualification, and vendor maintenance provisions to assure that an extended surveillance interval does not result in exceeding the assumptions