Regulatory Guide 1.105
| ML003740318 | |
| Person / Time | |
|---|---|
| Issue date: | 02/28/1986 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| RG-1.105, Rev 2 | |
| Download: ML003740318 (4) | |
Revision 2*
0 ,;U.S. NUCLEAR REGULATORY COMMISSION February 1986 SREGULATO RY GUIDE
OFFICE OF NUCLEAR REGULATORY RESEARCH
REGULATORY GUIDE 1.105 (Task IC 010-5)
INSTRUMENT SETPOINTS FOR SAFETY-RELATED SYSTEMS
A. INTRODUCTION
Any information collection activities mentioned in this regulatory guide are contained as requirements in 10 CFR
Criterion 13, "Instrumentation and Control," of Part 50, which provides the regulatory basis for this Appendix A, "General Design Criteria for Nuclear Power guide. The information collection requirements in 10
Plants," to 10 CFR Part 50, "Domestic Licensing of CFR Part 50 have been cleared under OMB Clear Production and Utilization Facilities," requires, among ance No. 3150-0011.
other things, that instrumentation be provided to moni tor variables and systems and that controls be provided
B. DISCUSSION
to maintain these variables and systems within prescribed operating ranges. Revision I to Regulatory Guide 1.105, "Instrument Setpoints," was published in November 1976 in response Criterion 20, "Protection System Functions," of to the large number of reported instances in which Appendix A to 10 CFR Part 50 requires, among other instrument setpoints in safety-related systems drifted things, that the protection system be designed to initiate outside the limits specified in the technical specifications.
operation of appropriate systems to ensure that specified Using the method described in Revision 1 to Regulatory acceptable fuel design limits are not exceeded. Guide 1.105 and additional criteria on establishing and maintaining setpoints, Subcommittee SP67.04, Setpoints Paragraph (cXl)(ii)(A) of § 50.36, "Technical Specifi for Safety-Related Instruments in Nuclear Power Plants, cations," of 10 CFR Part 50 requires that, where a under the Nuclear Power Plant Standards Committee of limiting safety system setting is specified for a variable the Instrument Society of America (ISA) has developed on which a safety limit has been placed, the setting be a standard containing minimum requirements to be used so chosen that automatic protective action will correct for establishing and maintaining setpoints of individual the most severe abnormal situation anticipated without instrument channels in safety-related systems. This stan exceeding a safety limit. It also requires the licensee to dard is ISA-S67.04-1982, "Setpoints for Nuclear Safety notify the NRC of any automatic safety system mal Related Instrumentation Used in Nuclear Power Plants."e*
functions, to review the matter, and to record the results of the review. Setpoints that exceed technical Some key terms used throughout ISA-S67.04-1982 specification limits are considered a malfunction of an are not defined or have unclear applications. For cun automatic safety system. venience, the following information is provided: (1)
the definition of the term "safety limit" is contained in This guide describes a method acceptable to the NRC 1 50.36 of 10 CFR Part 50, (2) the term "allowable staff for complying with the Commission's regulations value" as used in the standard is consistent with the for ensuring that instrument setpoints are initially within usage in the bases sections of the Standard Technical and remain within the technical specification limits. Specification (STS),*** (3) the term "upper setpoint
"Copies are available from the Instrument Society of America, The Advisory Committee on Reactor Safeguards has P.O. Box 12277, Research Triangle Park, North CarolinaSpecifica
27709.
- NUREG-0103, Revision 4, "Standard Technical been consulted concerning this guide and has concurred tions for Babcock and Wilcox Pressurized Water Reactors"; NUREG
0123. Revision 3, "Standard Technical Specifications for General in the regulatory position. Electric Boiling Water Reactors (BWR/S)"; NUREG-0212, Revision
2, "Standard Technical Specifications for Combustion Engineering Pressurized Water Reactors"; and NUREG-0452.- Revision 4. "Stan dard Technical Specifications for Westinghouse Pressurized Water Reactors." Copies of NUREG-series documents may be purchased iMe substantial number of changes in this revision thas made it from the Superintendent of Documents, U.S. Goverrunent Print.
Impractical to indicate the changes with lines in the margin. ing Office, Poet Office Box 37082, Washihston, DC 20013-7082.
USNRC REGULATORY GUIDES Written comments may be suomitted to the Rules and Procedures Branch, DRR ADM, U.S. Nuclear Regulatory Commission, Regulatory Guides are Issued to describe and make avallable to the Washington, oC 20555.
public methods acceptable to the NRC staff of Implementing specific parts of the Commission's regulations, to delineate tech niques used by the staff In evaluating specific problems or postu- The guideo are issuea in tne following tun broad divisions:
lated accidents or to provide guidance to applicants. Regulatory Guides are not substitutes for regulations, and compliance with 1. Power Reactors 6. Products them Is not required. Methods and solutions different from those set 2. Research and Test Reactors 7. Transportation Out in the guides will be acceptable if they provide a basis for the 3. Fuels and Materials Facilities 5. Occupational Health findings requisite to the Issuance or continuance of a permit or 4. Environmental and Siting 9. Antitrust and Financial Review license by the Commission. 5. Materials and Plant Protection 10. General This guide was Issued after consideration of comments received from Copies of issued guides may be purchased at the current Government the public. Comments and suggestions for Improvements In these Printing Office price. Information on current GPO prices may be guides are encouraged at all times, and guides will be revised, as obtained by contacting the Superintendent of Documents, U.S.
appropriate, to accommodate comments and to reflect new Informa- Government Printing Office. Post" Office Box 37082 Wasnhngton, tlon or experience. DC 20013-7082. telephone (202)275-2060 or (202)27h-2171.
C. REGULATORY POSITION
limit" as used in Figure 1 of the standard is the same as "trip setpoints" as used in the aforementioned STSs ISA-$67.04-1982, "Setpoints for Nuclear Safety in that drift above the "upper setpoint limit" (standard) Related Instrumentation Used in Nuclear Power Plants,'
or "trip setpoint" (STSs) requires readjustment. establishes requirements acceptable to the NRC staff for ensuring that instrument setpoints in safety-related Paragraph 4.3 of the standard specifies the methods systems are initially within and remain within the for combining uncertainties in determining a trip set technical specification limits. The last section of ISA
point and its allowable values. Typically, the NRC staff S67.04-1982 lists additional standards that are referenced has accepted 95% as a probability limit for errors. That in other sections of the standard. Those referenced is, of the observed distribution of values for a particular standards not endorsed by a regulatory guide (or incor error component in the empirical data base, 95% of the porated into the regulations) also contain valuable data points will be bounded by the value selected. If information and, if used, should be used in a manner the data base follows a normal distribution, this corres consistent with current regulations.
ponds to an error distribution approximately equal to a "two sigma" value.
D. IMPLEMENTATION
Section 6 requires that "software qualification" be documented. Although there is no generally accepted The purpose of this section is to provide information definition in the nuclear industry for software qualifica to applicants and licensees regarding the NRC staff's tion, the industry has used ANSI/IEEE-ANS-7-4.3.2-1982, plans for using this regulatory guide.
"Application Criteria for Programmable Digital Computer Systems in Safety Systems of Nuclear Power Generating Except in those cases in which the applicant or li Stations," for verification and validation of computer censee proposes an acceptable alternative method for software used in safety-related systems. Regulatory complying with specified portions of the Commission's Guide 1.152, "Criteria for Programmable Digital Com regulations, the methods described in this guide will puter System Software in Safety-Related Systems of be used by the NRC staff in the evaluation of instru Nuclear Power Plants," endorses this standard. ment setpoints for safety-related systems with respect to the technical specification limits for the following Some of the considerations in documenting setpoint nuclear power plants:
drift are (1) the degree of redundancy of the channels for which the allowable limits have been exceeded, (2) 1. Plants for which the constructi6n permit is issue the type of instrument, including the instrument's after February 1986.
designed accuracy, function, and plant identification number, (3) the allowable value in the technical specifi 2. Plants for which the operating license applica cations, (4) the "as left" setpoint from prior surveillance, tion is docketed 6 months or more after February 1986.
(5) the measured setpoint, (6) the amount of adjustment in the reported occurrence and the current "as left" 3. Plants for which the applicant or licensee vol setpoint, and (7) the history of previous testing and the untarily commits to the provisions of this guide.
amount of any drift and adjustment in previous testing.
1.105-2
VALUE/IMPACT STATEMENT
guidance on establishing and maintaining setpoints in
1. BACKGROUND
response to the needs that were apparent from (1) a continuing large number of reportable occurrences and The most common cause of a setpoint in a safety
(2) the licensing review of methodology for specifying related system being out of compliance with plant allowable values and trip setpoints.
.technical specifications has been the failure to allow for a sufficient margin to account for instrument inaccura
2. VALUE/IMPACT ASSESSMENT
cies, expected environmental drift, and minor calibration variations. For example, in some cases, the trip setpoint 2.1 General selected was numerically equal to the allowable value and stated as an "absolute value," thus leaving no ISA-S67.04-1982 is considered state-of-the-art meth apparent margin for drift. In other cases, the trip odology for specifying and reviewing technical specifica setpoint was so close to the upper or lower limit of the tions on allowable values and trip setpoints, and mem range of the instrument that instrument drift placed the bers of the industry have incorporated this standard setpoint beyond the range of the instrument, thus into their internal procedures. Further, paragraphs nullifying the trip function. Other general causes for a
50.73(a) and (b) of 10 CFR Part 50 define when an setpoint being out of conformity with the technical LER is required and what is to be included in an LER,
specifications have been instrument design inadequacies respectively.
and questionable calibration procedures.
2.2 Value Revision I to Regulatory Guide 1.105, "Instrument Setpoints," was issued in November 1976 in response to The value to NRC operations and industry- is that the large number of instances reported in Licensee there would be (1) a systematic method for specifying Event Reports (LERs) of setpoints drifting outside and reviewing technical specifications on allowable values the limits specified in the technical specifications.
and trip setpoints, (2) more sophisticated methods Revision I provided general guidance for (1) specifying for specifying technical specifications, (3) a reduction in setpoints (by considering instrument drift, accuracy, and range) and (2) having a securing device for the set setpoint readjustments, (4) less chance for unwarranted reactor shutdown, and (5) fewer LERs and other report point adjustment mechanism.
able occurrences from the allowable limits of setpoints being exceeded.
The method described in Revision I to Regulatory Guide 1.105 has been incorporated into an Instrument
2.3 Impact Society of America Standard, ISA-$67.04-1982, "Set points for Nuclear Safety-Related Instrumentation Used The impact would be minimal as ISA-$67.04-1982 in Nuclear Power Plants." Revision 2 to Regulatory represents current industry practice that has been codified Guide 1.105 was developed to use the guidance of in a national consensus standard.
ISA-$67.04-1982. This revision provides more specific
1.105-3
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