ML20137T421

Rev 2 to Reg Guide 1.105, Instrument Setpoints for Safety- Related Sys

ML20137T421
Person / Time
Issue date:	02/28/1986
From:	NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:
References
TASK-IC-010-5, TASK-IC-10-5, TASK-RE REGGD-01.105, REGGD-1.105, NUDOCS 8602180348
Download: ML20137T421 (4)

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Revision 2' f

U.S. NUCLEAR REGULATORY COMMISSION February 1986

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OFFICE OF NUCLEAR REGULATORY RESEARCH REGULATORY GUIDE 1,105 (Task IC 010-5)

INSTRUMENT SETPOINTS FOR SAFETY RELATED ~SYSTEMC A, INTRODUCTION Any information collection activities mentioned in this regulatory guide are contained as requirements in 10 CI R Criterion 13, " Instrumentation and Co nt rol,"

of Part 50, which prosides the regulatory basis for this Appemlix A, " General Design Criteria for Nuclear Pow er guide. The informat ion collection requiremeats in 10 Plants," to 10 CFR Part 50, " Domestic Licensing of Cl2 R Part 50 have been cleared under OMB Clear-Production and Utilitation Facilities," requires, among ance No. 31504)011.

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 Setpomts," was published in November 1976 in response Criterton 20, " Protection Syst em Fu nct io n s,"

of to the large number of reported instances m w his h Appendix A to 10 CFR Part 50 requires, among other instrument set rotnt s in sa f et y-relat ed 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 I to Regulatory acceptable fuel design limits are not exceeded.

G uide 1.105 and additional criteria on estabbshing and 3

maintaining setpoints, Subcommittee SP67.04, Setpoints Paragraph (c)(1)(ii)(A) of 6 50.36, " Technical Specifi-for Safety-Related Instruments in Nuclear Power Plants, cations," of 10 CFR Part 50 requires that, w here 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 setromts of individual the most severe abnormal situation anticipated without instrument channels in ufety related systems. This stan-exceeding a safety limit. It also requires the licensee to dard is IS A-S67.041982, "Setpoints for Nuclear Safety-notify the NRC of any automatic safet y sy stem mal-Related Instrumentation Used in Nuclear Power Plants.""

functions, to review the mat t er, and to record the results of the review. Set pomts that exceed technical Some key terms used throughout IS A-S67.04 1982 specification limits are considered a malfunction of an are not defined or have unclear appbcations. For con-automatic safety system.

vemence, the following in formation is provided: (1) the definition of the term " safety hmit" is contained in This guide describes a method acceptable to the NRC s 50 36 of 10 CI R Part 50, (2) the term " allowable staff for complying with the Commission's regulations value" as used in the stanitard is consistent with the for ensuring that instrument setpoints are initially within u uge in the bases sections of the Standard Technical and remain within the technical specification hmit s.

Specification ( ST S)," ' (3) the term " upper set point

• Copies are avadable from the Instrument Sodety of America.

The Advisory Committee on Reactor Safeguards has PD 15" ' 12277. Research f riangle Park, North Carolina 27709.

• *

• Nil H I G -0101 R evision 4. " Standard Technical Specifica-been consulted concermng this guide and has concurred tions for Itahcock and W'dcos Pressurned Water Reactors";NUpl G in the regulatory position' o t 2 L Heusion 3. " standard Technical spenfications for General l lu trK lloilmg W ater Reactors (ll% H/$)", NURI G-0212 Heunion

2. " Standard t echnksl Specirications for combustion i ng nectmg Pressursted W ater Heat tors", and N U Hl.G 04s 2, Hevision 4. "Stan dard Te chnkal Specifkations for Westmghouse Pressurited W ater Heactors " ('opies of NU Hi G4eries dmuments may be purchased

'The substantial namber of changes in this revision has made it from the Superintendent of Ilocuments. U.S Government Print.

impractical to indicate the changes with knet in the margin.

ing Offise, Post Offite flou 37082, Washington, DC 20013 7082.

USNRC REGULATORY GUIDES Written comments may be submitted to the Rules and Procedures firanch. ORR

ADM, U.S.

Nuclear Regulatory Commission, Regulatory Guides are issued to describe and make avaltable to the Washington, Dd 20555.

publ6c methods acceptable to the NRC staff of im plementing specific parts of the commission's regulations, to deimeate tech-n60ues used by the staff 6n evaluating specific problems or postu-T he guides are issued in the following ten broad divillons' lated accidents, or to provide guidance to applicants. Regulatory Guldes are not substitutes for regulations, and compliance with

1. Power Reactors

6. Products them is not required. Methods and solutions dif ferent from those set

2. Research and Test Reactors

7. T ransportation out in the gu6 des wiH be acceptable 6f they provide a basis for the

3. F uels and Materials Facalsties

81. Occupational Health findings requisite to the issuance or continuance of a permit or

4. E nvironmental and 56tmg

9. Antitrust and Financial Review license by the Commission.

5. Materiais and Plant Protection 10. General This guide was issued af ter cons 6deration of comments received from Copies of 6ssued gu6 des may be purchased at the current Government the oublic. Comrnents and suggestions for improvements in these Prtntmg Office price. tnformation on current GPO prket may be guides are encouraged at att times, and gu6 des wiu be revised, as obtained by contacting the Superintendent of Oncuments U.S.

appropriate, to accommodate comments and to reflect new enforma-Government Prmting Of fice Post Of fue flon 3 7082, Washington, tion or exper6ence, 7C 200131082, telephone h02l215-2060 or (202)215-2111.

PDR REGGD WLAELM FE @

limit" as used in Figure 1 of the standard is the same C. REGULATORY POSITION as " trip setroints" as used 'in the aforementioned SI'Ss in that drift above the " upper setpoint limit" (standard)

IS A-S67.04 198 2,

" Set roint s for Nuclear Safety-or " trip setroint" (STSs) requires readjustment Relited Instrumentation Used in Nuclear Power Plants,'

esta 31ishes requirements acceptable to the NRC staff for Paragraph 4.3 of the standard specifies the methods ensuiing that instrument set roint s in sa fet y-relat ed for combining uncertainties in determining a trip set-systems are initially wit hin and remam withm the point and its allowable values. Typically, the NRC staff technical specification lim it s.

Ihe last section of ISA-has accepted 95% as a probabihty hmit for errors. That S67 04-1982 lists additional standards that are ref erenced is, of the observed distribution of values for a particular in other sections of the standard. T hose referenced error component in the empirical data base, 95% of the standards not endorsed by a regulatory guide (or incor-data points will be bounded by the value selected. If porated into the rt gulations) also contam saluable the data base follows a normal distribution, this corres-information and, if used, should be used in a manner ponds to an error distribution approximately equal consistent with current regulatiant to a "two sigma" value.

Section 6 requires that " software qualification" be D. IMPLEMENTATION documented. Although there is no generally accepted definition in the nuclear industry for software quahfica-The purpose of this section is to provide information tion, the industry has used ANSI /IEEE-ANS-7-4.3.2-1982, to applicant s and licensees regardmg t'

NRC st afi's

" Application Criteria for Programmable Digital Computer plans for usmg this regulatory guide.

Systems in Safety Systems of Nuclear Power Generating Stations," for verification and validation of computer Except in those cases in w hich the applicant or li-software used m safet y-relat ed sy stem s.

Regulatory censee proposes an acceptable alternatise met hod for Guide 1.152, " Criteria for Programmable Digital Com-complying with specified twrtions of the Commnsioni puter Sy stem Software in Safety-Related System s of reg ulatio n s, the methods dessribed in t his guide w ill Nuclear Power Plants," endorses this standard.

be used by the NRC staff in the evaluation of mstru-ment set points for sa fet y-relat ed sy st e m s with respect Some of the considerations in documenting setpoint to the technical speu ficat io n hnuts for the follow ing drift are (1) the degree of redundancy of the thannels nuclear pow er plants:

for which the a;10wable limits hase been exceeded, (2) the ty pe of in stru m ent, including the m st ru m en t's

1. Plants f or w hich the construction pernnt is issuei designed accuracy, function, and plant identification af ter I ebruary 1986.

number, (3) the allowable value in the technical specifi-cations, (4) the "as left" setpoint from prior surveill.!nce,

2. Plants for whah the operatmg license apphca-(5) the measured setroint, (6) the amount of adjustment tion is docketed 6 months or more atter l'ebruary 1956.

in the reported occurrence and the current "as le t t "

setpomt, and (7) the history of previous testing and the

3. Plants for whah the apphcant or heensee sol-amount of any drift and adjustment in previous testing.

untarily commits to the provisions of this guide.

l.105-2

VALUE/ IMPACT STATEMENT

l. BACKGROUND guidance on estabhshmg and maintatning set roints in response to the needs that were apparent from (1) a The most common cause of a setroint in a safety-continuing largc number of reportable occurrences and related system being out of com phance with plant (2) the licensing review of methodology for specityng techmeal specifications has been the failure to allow for allowable values and trip setroints.

a sufficient margin to account for mstrument inaccura-eies, expected environmental drift, and minor cabbration

2. VALUEllMPACT ASSESSMENT variations. For example, in some eases, the trip setpoint selected was numerically equal to the allowable value 2.1 General and stated as an absolut e v alu e,'

thus leav mg no apparent margin fer d rif t. In other ca ses, the trip IS A-S67.04-19 8 2 is considered statemf the-art met h-setroint was so close to the upper or lower hmit of the odology for specifying and reviewing technical specifita-range of the instrument that instrument drift placed the tions on allowable values and trip setpoints, and mem-setroint beyond the rance of the inst rum ent, thus bets of the industry have incorporated this standard nullifying the trip function. Other general causes for a into their internal procedures. Furt her, paragraphs setpoint being out of conformity with the technical 50.73(a) and (b) of 10 Cl:R Part 50 define w hen an specifications have been instrument design inadequacies LER is required and what is to be included in an Ll R, and questionable calibration procedures.

respectively.

R evision I to Regulatory Guide 1,105, "Instruraent 2.2 Value Setpoint s,'

was issued in November 1976 in response to the large number of instances report ed in Licensee The value to NRC operations and mdustry is t hat Event Report s (LERs) of setroints drifting outside there would be (1) a systematic method for specif ying the hmits specified m the technical specifications.

and reviewing technical specifi.ations on allowable values Revision I provided general guidance for (1) specifying and trip set points, (2) more sophistiuted met hods setpoints (by considering instrument drift, accuracy, and for specifymg technical specifications, (3) a reduction m range) and (2) having a securing device for the set-set roint readjustments (4) less chance for unwarranted point adjustment mechanism.

reactor shutdown, and (5) fewer L1 Rs and other regurt-able occurrences from the allowable hmits of setpomts The met hod described in Revision I to Regulatory being excceded.

Guide 1.105 has been incorporated into an instrument Society of America Standard, ISA-S67.04195 2, " Set-2.3 Impact points for Nuclear Safety-Related Instrumentation Used m. Nuclear Power Plants.'

Revision 2 to Regulatory The impact would be minimal as ISA-Sh7 04-1982 Guide 1.105 was des eloped to use the guidance of represents current industry prastice that has been toitied ISA Sb7.04-1982. This revision provides more specific in a national consensus standard.

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