ML20083A654
| ML20083A654 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 08/19/1991 |
| From: | Cockerill A, Dabinett J CAROLINA POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML20083A646 | List: |
| References | |
| DG-VIII.50, NUDOCS 9109240223 | |
| Download: ML20083A654 (26) | |
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I CAROLINA POWER AND LIGHT COMPANY NUCLEAR ENGINEERING DEPARTMENT INSTRUMENT SETPOINTS DESIGN GIIIDE NUMBER DG-VIII.50 Revision Submitted Anoroved 0 John Dabinett A. Cockerill 1 ffy y htlff ,
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DESIGN GUIDE No. DG-VIII.50 Page i INSTRUMENT SETPOINTS Rev. 1 L.1p_'t OF EFFECTIVE PAGES EAR 891 1 1 2 1 3 1 4 1 5 1 6 1 7 1 B 1 9 1 10 1 11 1 12 1 13 1 14 1 15 1 16 1 17 1 3d 1 19 1 20 1 21 1 22 1 23 1 24 1
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% 2 DESIGN GUIDE No. DG-VIII.50 Page 1 TNSTRUMENT SETPOINTS Rev. 1 Table of Contents List of Effective Pages . . . . . . . . . . . . . . . . . i Table of Contents . . . . . . . . . . . . . . . . . . . . 1 1.0 INTRCDUCTION !
l 1.1 Purpose . . . . . . . . . . . . . . . . . . . 3 1.2 Scope . . . . . . . . . . . . . . . . . . . . 3 1.3 Applicability . . . . . . . . . . . . . . . . 3 2.0 GDIERAL )
1 2.1 Background . . . . . . . . . . . . . . . . . 4 1 2.2 References . . . . . . . . . . . . . . . . . 4 i 2.3. Definitions . . . . . . . . . . . . . . . . . 5 !
2.4 Abbreviations . . . . . . . . . . . . . . . . 8 3.0 . METHODOLOGY 3.1 Introduction . . . . . . . . . . . . . . . . 9 3.2 Objective . . .. . . . . . . . . . . . . . . 9 3.3 Categories of Uncertainties . . . . . . . . . 9 3.4 combination of Terms .. . . . . . . . . . . 12 4.0 SETPOINT RELATIONS!!IPS 4.1 Safety Limit . . . . . . . . . . . . . . . . 13 4.2 Analyti.'al Limit . . . . . . . . . . . . . . 13-4.3 Allowable Values . . . . . . . . . .. . . . 13 4.4 Trip Setpoint . . . . . . . . . . . . . . . . 15 5.0 DETERMINE INSTRUMENT CHANNEL SETPOINT 5.1 Introduction . . . . . . . . . . . . . . . . 16 5.2 Calculation Format . . . . . . . . . . . . 16 5.3 Instrument Loop Diagrams . . . . . . . . . . 16 5.4 Establish Analytical Limit . . . . . . . . . 17 5.5 Collect Instrument nd Environmental Data . . 17 5.6 Identify Design Parameters and Sources . . . 18 of Uncertainties l 6.7 Calculate Uncertainties for Each Module . . . 18 6.8 Determine Allowable Value and Trip . . . . . 19 Setpoint
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- DESIGN' GUIDE-No. DG-VIII.50 -Page - -2 INSTRUMENT SETPOINTS Rev. 1-Table of Contents (Cont'd) 6.0 EVALUATING EXISTING SETPOINTS :
l 6.1 Methodology. . . . . . . . . . . . . . . . . . 19_ l
'6.2 Existing Conservative Setpoints . . . . ... 19 l 6.3 Existing Non-Conservative Sotpointo . . . . . 20 l Figures.. .- - . . . . . .. . . . . . . . . . . . . . . . 21 Appendix'A . . . . . . . . . . . . . , . . . . . . . . 23 I
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DESIGN GUIDE No. DG-VIII.50 Page 3 INSTRUMENT-SETp0INTS Rev. 1
1.0 INTRODUCTION
1.1 Purpose 1.1.1 The intent of this guideline is to establish a consis-tent methodology for use in the preparation of instru-ment setpoint calculations for each of the three CP&L Nuclear plants.
1.1.2 A systematic method of identifying and combining in-strument uncertainties is necessary to ensure that vital plant protective features are actuated at the appropriate time during normal and accident conditions. .
1.1.3 This guideline adopts the methodology contained in ISA RP67.04, Part II titled " Methodologies For The Determi-nation Of Setpoints For Nuclear Safety-Related Instru-mentation".
1.2 scope 1.2.1 This guideline is applicable to all nuclear safety related process instrumentation that require setpoints for alarms, interlocks, permissives, time delays, prc-tective functions, automatic actuation, personnel safe-ty, or other reasons that require a documented basis for the instrument setpoint that is chosen. This de-sign guide may be used for non-safety related instru-ment loops as appropriate.
1.2.2 The scope of this design guido specifically excludes the following:
- Safety or-Relief Valves
- Self Contained Regulating Valves t
- Breaker Trip Settings
- Protective Relays
- Valve Torque or Limit Switches 1.3 Applicability 1.3.1 This guideline applies to NED personnel, including NED-managed contract personnel.
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DESIGN GUIDE No. DG-VIII.50 Page 4 INSTRUMENT SETPOINTS Rev. 1 2.0 GENERAL 2.1 Backcround 2.1.1 The requirement to docu=ent instrument setpoints is de-fined in References 2.2.7. Although not all of the_
CP&L plants have Regulatory (NRC) commitments to these references, it is the intent of this Design Guide to invoke adherence to the guidance specified in these References on the corporate engineering level. This will insure that the approach to developing instrument setpoints is consistent for all of the facilities, and consistent with industry practice and trends in this area.
2.2 References 2.2.1 Regulatory Guide 1.105, " Instrument Sotpoints", Revi-sion 1 2.2.2 ANSI /ISA Standard S67.04-1988, "Setpoints for Nuclear Safety-Related Instrumentation 2.2.3 ISA-RP67.04, Part II, " Methodologies for the Determina-tion of Setpoints for Nuclear Safety Related Instrumen-tation", Draft 9, March, 1991 2.2.4 NRC Information Notice 89-68, " Evaluation of Instrument Setpoints During Modifications", September 25, 1989 2.2.5 "Setpoint Change Control Program", INPO 84-026 Revision 01,_ Good Practice TS-405, June 1986 2.2.6 NED Guideline E-4, Preparation, Documentation, and control of Calculations 2.2.7 Nuclear Regulatory Commission Code of Federal Regula-tions - 10CFR50 Appendix B i
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I DESIG11 - GUIDE lio. - DG-VIII . 50 Page __ 5 IllSTRUMEliT SETPOI!1TS Rev. 1 2.0 GENERAL 2.3 Definitions 2.3.1 Safety Limits 2.3.1.1 A limit on an important process variable that is necessary to reasonably protect the integ-rity of physical barriers that guard against uncontrolled release of radioactivity.
2.3.2 Analytical Limit 2.3.2.1 A limit of a measured or calculated variable which forms the basis in the safety analysis to ensure that a safety limit is not exceed-ed. Analytical Limits are established with formal calculations performed by the Disci-pline Engineering Unit having responsibility for the plant system with which the instru-ment loop is associated.
2.3.3 Allowable Value 2.3.3.1 The limiting value that the trip setpoint can have when tested periodically, beyond which the channel is declared inoperable and cor-rective action must be taken. The Allowable Value is established as that value which is removed from the Analytical Limit by a magni-tude of process variable equivalent to the statistical sum of the unmeasurable uncer-tainties plus whatever conservative margin may be desired (Reference Figure 1).
2.3.3.2 In the case of Tech. Spec. Related instru-ments, if during periodic surveillance test-ing, the "As-Found" loop output is found beyond the Allowable Value, the loop is de-clared inoperable and reportability notifica-tion is initiated.
2.3.3.3 For specific discussion of the Allowable Value as it is to be applied at each of the three CP&L lluclear Power Facilities, refer to Section 4.3.
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, DESIGN GUIDE <!io. DG-VIII.50 Page 6
- INSTRUMENT SETPOINTS Rev.- 1-
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GENERAL
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2.0 2.3 Definitions (Cont'd) 2.3.4 Operatina Marcin 2.3.4.1 The difference between the trip setpoint and the maximum operating transient, o
4 2.3.5 Module 2.3.5.1 A portion of the instrument loop _or channel which can - be analyzed independently of . the other portions of the loop for instrument inaccuracy.
2.3.6 -Sauare Root Sum of the Scuares 2.3.6.1 The terms of the addition are added as the squares of the numbers and that whole sum is square rooted.
2.3.7 TI,in Setooint or Setooint 2.3.7.1 A predetermined value at- which a bistable device- changes - state to indicate that .the quantity under surveillance -has reached the:
selected.value. The Trip)Sotpoint.is estab-lished as that value which is removed from the Allowable Value_by a magnitude of process-variable. equivalent to the statistical sum of
- the -measurable ' uncertainties . plus whatever conservative margin-may be desired (Reference Figure 1).
- . 2.3.8 Calibrated Scan l
The magnitude of the difference between; the l
p 2.3.8.1 maximum- calibrated upper range val _ue. and - the minimum calibrated lower _ range-value.
2.3.9 Maximum Scan i
E 2.3.9.1 The - magnitude of the difference between the instrument's maximum upper range limit and its minimum lower range limit. ' '
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- -s DESIGli GUIDE 110. DG-VIII.50 Page IllSTRUMEliT SETPOIliTS Rev. 1-1 l
l 2.0 . GENERAL 2.3 Definitions (Cont'd)
- 2. 3.10 Turndown Ratio 2.3.10.1 The ratio of maximum span to calibrated: span for an instrument.
2.3.11 Qenendent Uncertainty 2.3.11.1 . Uncertainty _ components are dependent on each other if they possess a significant correla-tion, for- whatever cause, known or unknown.
Typically, dependencies form when effects share a common cause.
2.3.12 Indeoendant Uncertainty 2.3.12.1 Uncertainty components are. independent- of each other if their magnitudes or algebraic _ i signs are not significantly correlated.
2.3.13 Random
2 ~. 3 .13 .1 Describing -a variable - whose value at a par- '
-ticular' future instant cannot be predicted exactly, but can only_ be _ estimated'. The
- algebraic sign of a random uncertainty is-likely to be equally positive or negative with respect to-some median value.
l ' 2 '. 3 .14 - Limitina Safety System Settinas 2.3.14.1' Settings for_ automatic. protective devices re-lated to those variables: having significant 11
-safety functions.
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DESIGN GUIDE No. DG-VIII.St. Fage R INSTRUMENY SETPOINTS Rev. 1 2.0 GENERAL 2.4 AbbreviatigAg AV - Allowable Value AL - Analytical Limit RA - Reference Accuracy DE - Drift Effects M&TE - Maintenance & Test Equipment PSE - Power Supply Effects NTE - Normal Temperature Effects ATE - Abnormal Temperature Effects HE - Humidity Effects RE - Radiation Effects SE - Seismic Effects SPE - Static PreLsure Effects OPE - Over Pressure Effects IR - Insulation Resistance SRSS - Square Root Sum of the Squares DBA - Design Basis Accident SSE - Safe Shutdown Earthquake LOCA - Loss of Coolant Accident HELB - High Energy Line Break UE - Uncertainty Error LSSS - Limiting Safety System Settings
DESIGN GUIDE No. DG-VIII.50 Page 9 INSTRUMENT SETPOINTS Rev. _ 1 3.0 KETHODOLOGY 3.1 Introduction 3.1.1 The setpoint methodology presented in this design gwide identifies the major sourcos of instrument uncertainty and presents a method for combining these uncertainties which, while conservative in nature, is not unnecessar-
. ily restrictive with respect to plant operations.
3.2 obiective 3.2.1 The objective of this methodology is to be able to predict the values of uncertainty associated with in-strument loop, which can reasonably be expected given a certain set of conditions.
3.3 Catecories of Uncertainties 3.3.1 Random Uncertaintiqn 3.3.1.1 Random uncertainties are those that a manu-facturer specifies as having a t magnitude.
A random uncertainty is considered to be zero contered and approximately normally-distrib-uted represented by a " Bell" curve. These types of errors are combined statistically as the " Square Root of the Sum of the Squares" (SRSS).
5.3.2 Indeoendent Uncertainties 3.3.2.1 Independent uncertainties are those uncer-tainties for which no common root cause ex-ists. It is generally accepted that most instrument channel uncertainties are random and independent of each other. However, this determination must be made on a case-by-case basis, i
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DESIGN GUIDE No. DG-VIII.50 Page 10 INSTRUMENT SETPOINTS Rev. 1 3.O METHODOLOGY 3.3 Catecories of Ung9rtainties (Cont'd) 3.3.3 Denendent Uncertainties 3.3.3.1 Dependent uncertainties may exist between some uncertainties because of the complicated relationships which may exist between the instrument channels and various instrument uncertainties. The methodology presented in this Guideline provides a conservative means for addressing these dependencies. If, in the user's evaluation, two or more uncertain-ties are believed to be dependent, then, under this methodology, these uncertainties should be added algebraically to create a new, larger independent uncertainty.
3.3.3.2 As an example, the Rosemount line of dif fer-ential pressure transmitters, the vendor states that there ic a span shift in the transmitter while operating at high static pressure. Therefore, the reference accuracy of the transmitter, which is given in percent of span, is dependent on the span effects due to operating at high static pressure. That is the overall reference accuracy of the transmitter will vary as a result of the operating static pressure effects.
3.3.4 Bias 3.3.4.1 A bias is a systematic instrument uncertainty which is predictable for a given set of con-ditions because of the existence of a known magnitude and direction (positive or nega-tive).
3.3.4.2 The different categories of bias will be handled in different manners. Bias errors of known magnitude and direction will be cali-brated out of the system. An example for that would be the change in density of a process at elevated temperature and pressure would be calibrated out of the level transmitter error analysis. The only bias errors that will be treated separately are bias errors with a known direction and an unknown magnitude.
These will be added to its bias direction errors. i.e. add the negative biases to each other and the positive biases to each other. 3 1
l DESIGN GUIDE No. DG-VIII.50 Page 11 INSTRUMENT SETPOINTS Rev. 1
-3.O METHODOLOGY 3.3 Catecories of Uacertainting (Cont'd) 3.3.5 Arbitrarilv-Distributed Uncertainties 3.3.5.1 Some uncertainties are not normally distrib-uted. Such uncertainties are not eligible for SRSS combinations and are categorized as arbitrarily distributed uncertainties. Such uncertainties may be random (equally likely to be positive or negativc with respect to some value) but extremely non-normal. That is, it can not be statistically represented i by a " Bell" curve. .
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3.3.5.2 This type of uncertainty is treated as a bias against both the positive and negative compo- !
nents of a module's uncertainty. Because '
they are equally likely to have a positive or a negative deviation, uorst-case treatment ,
should be used, i 3.3.6 Unmeasurable Uncertainties 3.3.6.1 Unmeasurable uncertainties are those uncer- '
tainties that are either not present or are ,
not measured during periodic testing. These j values may include the following effects: l
- Fluid Density Effects
- Flow--Meter Accuracy
- Static Pressure Effects
- Accident (Temperature, Radiation, and Seismic) Effects l
3.3.7 Measurable Uncertainties 3.3.7.1 Measurable uncertainties are those uncertain-ties which may be present during normal chan-nel calibration. The following are some examples of measurable uncertainties:
- Reference Accuracy Drift Effects .
- Normal Temperature Effects
. Static Pressure-Effects
- Maint. & Test Equip. Effects
- Power Supply Effects i
- Humidity Effects l
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DESIGN GUIDE No. DG-VIII.50 Page 12 INSTRUMENT SETPOINTS Rev. 1 3.0 METHODOLOGY 3.4 CombinaLtion of Terms 3.4.1 Determination of maximum loop uncertainty on the basis of a " Straight Sua" methodology assumes that all un-certainties occur at the same time, at their maximum values, and all in the same direction. While this method provides almost 100% assurance that the derived uncertainty is conservative, it is likely that these setpoints would be set too deep into the normal operat-ing ranges of a parameter.
3.4.2 Use of a Square Root Sum of the Squares (SRSS) method-ology for independent, normally distributed uncertain-ties, assumes that the elements of uncertainty are free to vary in both direction and magnitude which is sta-tistically more valid than the " Straight Sum" methodol-ogy.
3.4.3 The basic formula for uncertainty calculation takes the form of:
+ C') "' !!Fj)
- 2 Z = [(A 'B +L-M where:
A, B, C = random and independent uncertainty terms.
F = arbitrarily distributed uncertainties.
L and M = biases with known direction.
Z = Resultant Uncertainty 3.4.4 In the determination of the random portion of an uncer-tainty, situations may arise where two or more random terms are not totally independent of each other but are independent of the other random terms. This dependent ,
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relationship can be accommodated within the SRSS meth-odology by algebraically summing the dependent random terms prior to performing the SRSS determination. The formula takes the following form:
Z = [ ( A' + B +C) + (D + E) )" tlFj +L-M wh.ere:
D and E = random dependent uncertainty terms.
DESIG11 GUIDE 110. DG-VIII.50 Page 13 IllSTRUMEllT SETPOINTO Rev. L,__
4.0 SETPOINT RELATIONSHIPS Sotpoint relationships are discussed colow and are also illustrated on rigures 1 and 2.
4.1 pafety Limit 4.1.1 Safety limits are determined primarily by the NSSS ven-der to protoce the integrity of physical barriors that l I
guard against the uncontrolled release of radioactivi-ty. The safety limits are provided in the plant toch-nical specifications and FSAR safety analysis.
4.2 AtLalvtical Limit 4.2.1 The Analytical Limit is established to ensure that the safety limit is not oxcoodod. The datormination of Analytical Limits are the responsibility of tha Engi-nooring Disciplino responsible for the plant system with which the loop is associatod.
4.2.2 All instrument setpoints that are analyzed under this guideline must establish a basis for the Analytical Limit. This value must be datormined through an engi-neoring calenlation or other appropriato means of anal-ysis and documented in the specific notpoint calcula-tion. Allowable values, and ultimately trip sotpoints, will be based on the Analytical Limit valuo.
4.3 Allowablg_yALRg1 ,
4.3.1 In ISA 67.04 terms, the Allowable Value (AV) is con-sidered the value that the trip notpoint can have when tested periodically, beyond which the instrument chan-l nel should be evaluated for operability. In the caso l of an increasing process, the Allowablo value is dotor-l mined by subtracting the statistical cum of all the applicable unmeasurablo uncertaintion (UM) from the Analytical Limit ( AL) value. At the discrotion- of the l
l engineer performing the sotpoint calculation, an addi-l tional margin may be allowed in the region with unmoa-surable uncertaintios for the pt.rpose of adding consor-l vatism away f rom the Analytical Limit. The Allowable L
! Value for increasing process would thus be given as:
OESIGli GUIDE !!o. DG-VIII.50 Page 14 IllSTRUMEllT SETPOINTS Rev. 1 4.0 SETPOINT RELATIONDHIPS 4.3 hl19yalglg Valuen (Cont'd) 4.3.2 For a decreasing process, the unmeasurablo uncertain-ties are added to the Analytical Limit:
AV = AL + (UM + Margin) e 3 Carotul consideration should be given to assigning con-servativo margins to ensure that normal system opera-tion is rSt compromised.
4.3.4 ny applying this methodology, it is evident that during calibration testing, if a trip actpoint is found to be below the Allowable Value, there is amplo margin from the Analytical Limit to ensure that the trip sotpoint would not exceed the Analytical Limit when exposed to the effects of a Design Basic Accident, Soismic ovent, or process measurement offects.
4.3.5 The Tech tical Specifications at each of the throo CP&L nuclear plants contain Instrument Sotpoint limits, which if exceeded, are considorod as reportable events.
Plant specific terms must be reconciled with the ISA terminology for the purpose of establishing reportable limits.
4.3.6 In many casos the Tech. Spoc. value may be the only limiting value provided. Unless a calculation can be found which establishes an Analytical Limit, then the Tech. Spec. value is to be taken as the ISA Analytical Limit. The assumption is that the now Allowable Value (Tech Spec. Value) and trip sotpoint would be very conservative if the existing Tech. Spec. Value is taken as the Analytical Limit. If at all possible, this situation should be avoided and an Analytic Limit should be established to support the existing Toch.
Spoc value.
4.3.7 When using the Tech. Spec value as the Analytical Lim-it, an Allowablo Value should be calculated in accor-dance with the ISA methodology for reportability pur-poses. That is, the Allowablo Value equals the Toch.
Spec. value minus the statistical sum of the Unmeasur-able Uncertainties. This distinction betwoon the Tech.
Value and the calibration Allowablo Valuo must be re-flected on the appropriate Maintenance and Surveillance test procedures.
DESIG11 CUIDE 110. DG-VIII.50 Page 15 IllSTRUMEliT SETPOINTS Rev. 1 4.0 SETPOINT RELATIONS 11IPS 4.3 hilowablo Valuen (Cont'd) 4.3.8 Since the above discussion represents a very conserva-tive approach, adopting it for all casos may put re-strictions on the operation of the system. This can be avoided by having the responsible disciplino calculate more realistic Analytical Limits which would permit the Tech Spoc. values to be taken as ISA defined Allcwable Values.
4.4 Irlp 8olp_oing 4.4.1 The trip setpoint is a prodotermined value at which a bistable module changes stato to indicate that the quantity under curveillance has reached the selected value. The trip cotpoint is established to ensure that when the offccts of all uncertaintion are imposed on the loop, there will bo sufficient margin to ensure that the Analytical Limit would not be excooded.
4.4.2 Since the region between the Analytical Limit and the Allowable Value accounts for the Unmeasurable Uncer-tainties associated with a particular loop, the Trip Setpoint would be movo< away from the Allowablo Value by a magnitudo of the process variable that is greater than or equivalent to the statistical sum of the mea-surable variables. The Sotpoint equation could be expressed as follows:
S P = AL - (MU + UM + Margin) 4.4.3 .t should be stated again that the margin factor is op-tional and arbitrarily selected to add conservatism to the setpoint value.
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DESICl3 CUIDE No. DG-VIII.50 Page 16 INSTRUMENT SETPOINTS Rov. 1 5.0 DETERMINE INSTRUMENT CHANNEL SETPOINT 5.1 Introducti2D 5.1.1 The following discussion providos a suggested sequence :
of stops to be performed when developing an instrument channel uncertainty or sotpoint analysis. This discus-sion is intended as general guidanco. For a moro do- ,
tailed description of sotpoint methodology and sample calculations, refer to the recommended practico associ-ated with ISA Standard S67.04.
5.2 QAlgulation Formd 5.2.1 Final instrument notpoint values are to be documented by forr I calculation. The calculations may be por-formod ,y " hand" or proforably, by applying the to-chniques of a computer bar.od word processor. An alter-nato method would employ tho use of a specifically designed computer based software program. The final calculation must be design verified if the computer program used has not' boon validated and verified.
5.2.2 Regardless of the method used to prepare the calcula-tion, each calculation is expected to contain as a minimum, the following sections:
- List of Effectivo Pagos
- Table of Contents
- Objectiva
- Functional Description
- Roterences
- Inputs and Assumptions
+ Dotormination of Uncertaintion
- Calculation of Uncertainties
- Discussion.of Results
- Loop Diagram 5.3 Instrument Loop Diao ng 5.3.1 When preparing an uncertainty or notpoint calculation it-is helpful to generato a diagram of the instrument channel being analyzed. A diagram aids in developing the analysis, classifying the uncertainties that may be present in each portion of the instrument channel, L datormining the environmental paramotors-to which each i portion of the instrument channel may be exposed, and i identifying the appropriato module transfer functions.
DESIGN GUIDE No. DG-VIII.50 Page 17 INSTRUMENT SETPOINTS Rev. 1 5.0 DETERMINE INSTRUMENT CHANNEL SETPOINT 5.3 Eggnpre the Instrument Loop Diaorga (Cont'd) 5.3.2 Figuro 2 represents a typical loop diagram for an in-strument loop analysis. Similar diagrams may be used provided the following pertinent information is includ-od:
- Process Units
- Primary Element
- Process Transmitter
- Secondary Electronic
- Output Devices
- Loop Signal Types 5.3.3 If it is questionablo whether a particular modulo or uncertainty element should be analy od because it may alot have an appreciable amount of error associated with it, the module or uncertainty nood not be accounted for in the calculation as long as the basis is documented in the calculation. If a random indopondent uncertajn-ty is 5 times smaller than the largost random indepen-dont uncertainty, it is not to be considered statisti-cally significant.
5.4 KatAblish Analytical Limit 5.4.1 The development of the Analytical Limit is outsido the scope of this guidelino. It is desirable that Analyt-ical Limits for the various plant processos be dator-mined by the responniblo engineering discipline groups.
For purposes of this guideline, the bases for the Ana-lytic Limit must be documented in the sotpoint calcula-tion.
5.5 collect Instrument and Environmental IDformati2D 5.5.1 The information about the area and environment will be required for each module. If the modulo has a variety of changing areas such as a cable which traverso through harsh and mild areas, then it may be casier to ovaluato each section as a differont modulo.
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DESIGN GUIDE llo. DG-VIII.50 Page 18 ,
IllSTRUMENT SETPOINTS Rev. 1 S.0 DETERMINE INDTRUMENT CIIANNEL BETPOINT 5.6 Identi f y Dopign. PetramjttgIs gI.d_I!p.urcos of Uacertainty 5.6.1 The functional requirements, actuation functions, as well as the environmental conditions that the loop components will be exposed to should be identified.
The following represents a typical listing, but should not be considered all inclusivat
. Reference Accuracy
. Drift Accuracy
. Temperature Effect
. Radiation Effect
. Seismic Effect
. Humidity Effect
. Static Pressure Effect
. Maintenance and Test Equipment
. External Bias 5.6.2 Any assumption used in datormining that an error sourco does not apply to that module should be stated in the calculation.
5.7 9_qlq11Jate Uncertainties for Eag.b HQdMla 5.7.1 It is recommended that too uncertainty values calculat-ed must have the same basis in order to combine the errors. The common basis is typically the calibrated span of the transmitter. A discussion in Appendix A shows techniques for the conversion of other basis of ercora to the calibrated span basis. The errors are to be categorized as to their type of uncertainty (Random, Bias, or Arbitrarily Distributed).
5.7.2 Prior to combining the loop uncertainties, a determina-tion must be mado.as to whether a particular uncertain-ty would be present during calibration (Measurable Un-cortainty), or whether the particular uncertainty would be associated with process or accident effects (Unmea-surable Uncertainties). Reference Section 3.3.
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INSTRUMENT SETPOINTS 1 1
5.0 DETERMINE INSTRUKENT CRAWNEL SETPOINT .
5.8 Q1t.gI d ne Allowable Value and Trio setDoint ;
5.8.1 Those uncertainties that are considered an unmeasurable i during calibration are to be combined using the basic i formula contained in Section 3.4. The resultant uncer-i tainty plus any additional margin is to be applied against the Analytical Limit for determining the Allow- <
able Value for the loop. (Reference Section 4.3 and '
Figure 1) 5.8.2 Those uncertaintics that are considered as measurablo ,
during calibration are to be combined using the basic l' formula contained in Section 3.4. The resultant uncer-
, tainty plus any additional margin is to be applied .
. against the Allowable value 4.n order to establish the i Trip Setpoint for the loop. (Referenco Section 4.4 and Figuro I. l 6.0 -EVALUATING EXISTING HETPOINTS [
6.1 Methodology 6.1.1 The process for ovaluating existing setpoints should be i the same as for establishing now sotpoints. That is, '
the methodology relating to the determination of uncer . .
tainties and the combination of terms must be in accor- ,
e dance with this design guide.
6.1.2 It is expected that since the existing setpoint analy- ,
. sis did not use the same methodology, or account for
- all the same uncertainties that are contained in this I guide lino, a new setpoint value different than the '
existing setpoint would be datormined.
6.2 Distina cong.grvative setplintA -
6.2.1 If the.new setpoint value is determined to be'conserva-tivo--with respect to the existing setpoint,-it is like -
ly due to the existing analysis containing an excessive amount of conservatism. The new setpoint calculation <
- could adopt the additional margin of conservatism and '
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leave the setpoint value unchanged or process a set-i point change -document which would effectively change-i the setpoint value of.the loop. This datormination is i to be made on a project basis with the concurrence of the Lead Project Engineer or Disciplino Principal Engi- t p neer. .
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_ . _ . , - . . _ _ _ _ _ _ . _ _ _ _ . . _ _ . , _ , , . _ _ . . . . _ . _ _ . , _ _ _ _ _ _ _ . , _ . , .,, _ ,,,, ...,,, ,. ., ,_,.__ , _.._,... ,__., _ _._ , a . _
s DESIGN GUIDE 11o. DG-VIII.50 Page 20 IllSTRUMENT SETPOINTS Rev. 1 l
6.0 EVALUATING EXIDTING BETPOINT8 !
1 6.3 RKijtina Non-Cqmfrvative BetPJ2iD_t.
6.3.1 In the event that the now calculation has datormined that the existing setpoint value is non-conservativo with respect to the new calculated values, several op-tions must be considered for reconciling the differ-onco.
- 1. Review the calculation for conservatism that can be removed.
- 2. Review the process limit calculation to dator-mino if there is any conservatism in the Ana-lytical Limit calculation that can be removed.
- 3. Review environmental zones to determino if lo-cation specific environmental paramotors are less scvoro than the paramotors used in the calculation.
6.3.2 If the above efforts fail to reconcile the non-consor-vativo differences with the existing sotpoint value, consideration should be given to calculating applicable uncertainties based on a reduced calibration interval.
This approach, if successful, would require would re-quire a revision to the associated plant test proco-duros.
6.3.3 If all efforts fail to reconciie now non-conservative values, then an initial review ahall be performed to quickly determine if an adverse condition exists. If an adverse condition exists, then the discrepancy could have pctantial safety significance. If the discrepancy does not raise a safety concern based on the results of the initial review, it can continue to be evaluated and dispositioned on a lower priority. If the discropancy is determined to be potentially safety significant, it will be processed as an adverso condition por NED Pro-cedure 3.18 and undergo both operability and reporta-bility evaluations. The initial review shall be com-pleted promptly after identification of a non-conserva-tive setpoint.
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l DESIGN GUIDE No. DG-VIII.50 Page _ 21 INSTRUMENT SETPOINTS Rev. 1 FIGURE 1 DETERRIE T10!i 0F IllSTRUMEllT SETPolllTS AllD ALLOWABLE VALUEE
- Artly LIMIT l
ANAL f ilC AL L IN T MARGIN (NOTE 1) l'< ,,
/ /'/,/
_ ,,i,<'- ' ,' /, '
! qEr1 AINt g e 4 .. //// -
- gf;);[cvE[ {/i /,', UN-ME ASUG [ Alf E '// '
u t.c nacMot // ' -
UNc
,'(ND'[ C r] ','(',}
t ^:st, it : '/'(y( J,
DrEtATIDN //l,/,'
l ii ,
! Vj , jf :; '
- ALLOVAOLE ,ALLE MAkGIN tt[CH trEC 6 E F DL1 ARE LIMil)
(NOTE D
...........+
UNC E R T AIN i lE ; * * *
- MEASusEAptt * *+
CBiLEVED ,
- * * ~ UNC E & T AIN11E i ' , ' , * ,
OPEE AllDN , . . . . . . .....
'- TRIP SCTPOINT
~~-- -
MAX. T R AN0][tl T
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/. $ 7,[
4,'l/,',f,Q
, , _E _ ;; k_ ,, }[$[/ '///)
@; '/Q .; ':- artr AiING uNat/ - )',/g4, f.'/// ,,q
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u inu .o u// /9 ,i
. , v 7/,u <;;/,, _ /,69 /x
/,, i n HOTES 1, M ARGINS ARE OPil0N AL, AND A6RlIR ARlLY SELECTED AND APPLi[0 AGAIN$T THE ANALYTICAL Lvt AND/OR ALLO
- ABLE VALUE WHERE AN ADOlll0NAL uCA0VRt cr 70NSERVAll5M MAY DE DESIR(D.
L ut ASUR ABLE UNCERT AINIIES W AY LNCLUDE TWE FOLLOWING EFFECTS:
REFERENCE ACCURACY ORiri ErrECTS NORWAL TEWPER ATURE Ef rECTS STATIC PRLOSURE Err [Cf 5 f t$T EQUIPulNI ErrECTS POWER SUPPLY Ef f CCf 5 HUWIDITY EfrECTS
- 3. UN.WE ASUR ABLE UNCERT A:NiiES uAY INCLUDE THE FollowiNG EFFECTS:
SEtSuiC Erf ECT*>
RADIAfl0N ErrECTS FLUID DENSITY Ef r[ CTS ABNORW AL TEuPER ATURE EFFECTS
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I DESIGN GUIDE No. DG-VIII.50 Page 22 INSTRUMENT SETPOINTS _
Rev. 1 FIGURE 2 1YPICAL LOOP DIAGRAM ;
LOCAL vlEKERY S! MMS 4-C S PANGE' 0-170 INVC MAX, TEMPERATURE _ 'r MAX. PADIAi!CN ,,,_,_ R A D l ;
II I I i- 1 INSTR. RACK A1-R9 ,
-al
, TT L,,L :T EARicu 752
{ 01-cs) PCAL. 04 9ANGE: 0- 178 i'.WC s"'IM / PANGE: 0- 178 iNWC max 1 1CMPERATURE _ 'r OUTPUT SIGNAL: 4-20 uo MAX. PADI A TION RAD PROCESS INSTRUMENT CABINET C5 4-20 Mo max 1CHpERATUPC 'r 40V LCDP MAK RADIATION RAD NgN.jsot, WE %T INGHOUSE pDVEp TYPE NLPI OUFPLY MAIN . CQhlROL BOARD 1A2 g
> r! 0 CS-0130A V MAX. TEMPEPATURE 'r $ d WESTINCHOUSE VX-252 MAX. RADIAT!CN PAD ! ^LE INPU1: 0-10 VDC
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- 4
.e . -- -- == - e.
REACTOR C001A_N_I PUMP A
.S_E AL WATER FLOW LOOP 0130 (REr. 2166-s-rcso130) l'
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DESIGN GUIDE No. DG-VIII.50 Page 23 INSTRUMENT SETPOINTS Rev. 1 APPENDII_A Conversion-of Error Basis Thet error basis which provide the most flexible and aseful informa- l tic,n is expressed as a percentage of the instrument calibrated span'. The- instrument may be specified us;ing a dif ferent- basis for ,.
the error term. ;,
The following_ techniques are used to convert other error basis to a percentage of span basis.
Uocer Rance Limit - The upper range limit is associated with an in-strument which has adjustable ranges. The upper range limit (URL) is the-maximum range of the instrument. .
Error % Span =(Error % URL) (Process URL)/(Process Span) ,
i-For example, the drift accuracy ist-0.5% of upper range limit. The span is 0-100 psig and the upper' range limit of the transmitter is ',
0-400psig.
Error % Span =(i _0.5%) (400 psig)/(100 psig)
Error % Span = t 2.0 % i i;
lite Ranetes - The measurement and test equipment has a range which is different from the instrument range. The process span must be converted to the MTE units. !j Error % Span = (MTE % Error) (MTE span) i
! (Process Converted Range) ;;
For _ example, a - pressure transmitter has a process _ span of 0-100
psig.-The corresponding-signal is 4-20 made. This is dropped across l a 250 ohm resistor at the test point to produce a 1-5 Vdc signal.
The diaital multimeter has a voltage range of 0-25 vdc. The MTE i error is 0.2% range.
i Error % Span = (t 0.2' %) (25 volt)/(5-1 volt)
Error %_ Span = .i 1.25 %
t o'
- DESIGN GUIDE No. DG-VIII.50 Page 24 INSTRUMENT SETPOINTS Rev. 1 MPENDIX A (Cont 'd)
MTE error as a Percentace of Readinc - The error may be expressed as a percentage of the value. This is common for digithi meters.
Error % Span = (Process converted setpoint) (% Error of. reading)
(Process converted span)
For example, the test equipment has an accuracy of i 0.3 % of read-ing for all scales. The process span is 0-100 psig. The electrical output it 4-20 made. This is tested as a 1-5 vde signal across a 250 ohm resister. The setpoint is 50 psig.This corresponds to a 3 Vdc setpoint.
Error % Span = (3.0 vdc ) (t 0.3% )
(5-1 vdc)
Error % Span = 1 0.15%
B11s of a Known Maximum Mannitwig -A known bias can be converted to a percentage of span.
( cess Mas)
Error % Span = X 100 '
(Process span)
For example, the temperature bias in the reference leg of a level transmitter can cause a maximum error of 2 inwc. The transmitter has a span of 250 inwc. .
Error 1, Span =
( 50 n )
Error % Span = 0.8 %
lite Error with Roundina of Least Sianificant Dioits - The digital meters have an error associated with the rounding off or truncation of the least significant digits. If the device han four or more digits, then the error caused by the rounding of the fourth digit will not add an appreciable amount of error.
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