This Technical Report provides guidance on a graded approach for calculating and documenting channel and indication uncertainties as well as for documenting uncertainty-adjusted interlock values, setpoints, test acceptance criteria, and action points for permanently installed nuclear plant instrumentation.

Purpose

This Technical Report supplements the information provided in ISA-67.04.01 and ISA-RP67.04.02 for the determination of instrument channel uncertainty, instrument indication uncertainty, and instrument setpoints. Specifically, the topic addressed in this technical report is the use of a graded approach as mentioned in the Recommended Practice, where issues of higher safety significance are treated with greater rigor and issues of lower safety significance are treated with less rigor. Branch Technical Position HICB-12 allows such variations in rigor based on the safety significance of the instrument function.

Uncertainties for measurement and test equipment, laboratory instrumentation, and other nonpermanently installed or non-process instrumentation such a meteorological instrumentation are outside the scope of this document.

Other guidance and requirements exist for determining instrument uncertainties for other applications. Specifically, ASME sets forth requirements for In Service Testing instrumentation. Such alternate guidance is beyond the scope of this document.

Descriptions of and requirements for a full setpoint control program are beyond the scope of this document.