ML20010H704

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Plant Protection Sys Selection of Trip Setpoint Valves, Revision 00
ML20010H704
Person / Time
Site: San Onofre  Southern California Edison icon.png
Issue date: 11/15/1979
From:
ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:
Shared Package
ML13302A548 List:
References
1408-MAD-1, CEN-112(S), CEN-112S-R, CEN-112S-R00, NUDOCS 8109290163
Download: ML20010H704 (58)
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i San Onofre Nuclear Generating Station i Units 2 and 3 Docket 50 - 361

- 50 - 362 a

i CEN-112(S)

Revision 00 Plant Protecticr. System Selection of Trip Setpoint Values i

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NOV 151979 l

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t Combustion Engineering, Inc.

Nuclear Power Systems I Windsor, Connecticut 4

810*290163 810922 PDRADOCK05000g K

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,1408/caf-2 LEGAL NOTICE I

This report was prepared as an ac:ount of work sponsored by Combustion Engineering, Inc. Neither Combustion Engineering nor any. person acting on its behalf:

a. Makes any warranty or representatation, expressed or implied, including the warranties of fitness for a particular purpose or merchantability, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe on privately owned rights; or
b. Assumes any liabilities with respect to the use of, or for damages resulting from the use of, any information, apparatus, method or proc;ss disclosed in this report.

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ABSTRACT I

This report describes the Combustion Engineering " explicit" method of determining trip setpoint values for Southern California Edison San Onofre Nuclear Gene' rating Statior, Units 2 & 3 Plant Protection System. The " explicit" method has been estabeished, in part, to ensure that the Plant Protection System response will be consistent with the response assumed in the Safety Analysis, and to, ensure that the methodology used will be consistent with current licensing requirements and industry standards.

This report includes a tabulation cf specific data used in the setpcint determination process. This data provides the information requested by the Nuclear Regulatory Commission concerning the selection of trip setpoints for the SONGS Plant Protection System.

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r s 1408/caf-4 TABLES OF CONTENTS

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Cover i Legal Netice 11 Abstract 111 Table of Contents iv .

List of Tables v List of Figures vi List of Acronyms and Abbreviations vii Lis* of Definitions ix

1.0 INTRODUCTION

1.1 SCOPE 1-1

1.2 BACKGROUND

1-2 2.0 SETPOINT METHODOLOGY 2.1 BASIC DESCRIPTION 2-1 .

2.2 ANALYSIS SETPOINT .

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2.3 EQUIPNENT ERRORS 2-3

2. '4 SETPOINT DETERMINATION 2-8 2.5 CORE PROTECTION CALCULATOR ScTPOIN'TS 2-10
2. 6 RATE LI!!ITED YARIASLE SETPOINT 2-18 3.0 EQUIPMENT CALIBRATION 3.1 BASIC DESCRIPTION 3-1 3.2 SETPOINT DETERMINATION 3-1 3.3 TECHNICAL SPECIFICATIONS 3-2 3.4 CALIBRATION GUIDELINES 3-3 3.5 CPC CnLIBRATION 3-3 4.0 DETAILED SETPOINT DATA 4.1 NRC REQUEST 4-1 4.2 EXPLANATION OF TABLES 4-2 i

5.0 REFERENCES

4 TABLES FIGURES iv

1408/caf-5 i 1 LIST OF TABLES

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Table No. Title Page No.

1 PPS Trip Setpoints, Allowable Values and Drift Allowances 5-3 2 PPS Instrument Bias Components 5-4 3 FPS Instrument Bias components, Continue' 5-5 4 PPs Analysis Setpoints and Setpoint Margins 5-6 5 PPS Core ~ Protection Calculator Trip Setpoint Data 5-7 6 PPS Core Protection Calculator Process Equipment Bias Components 5-8 7 PPS Core Protection Calculator Process Equipment, .

> I Bias Components, Continued, and Total Allowances 5-9 l

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N08/ca'-6 LIST OF FIGURES

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Page No.

Figure No. Title 5-10 1 , Setpoint Calculation Methodology Analysis Setpoint Initial Determination 5-11 2

Plant Protection System Block Diagram 5-12 3

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- 4 Equipment Setpoint Determination Using Event Specific Data 5-13 5 Reactor Protection System Inputs and Trip Functions 5-14 6 Core Protection Calculator as Part of the Reactor Protection System 5-15 ,

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  • 1408/c2f-7 LIST OF ACRONYMS AND ABBREVIATIONS

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ACRS Advisory Committee on Reactor Safeguards A/D Analog to Digital Converter ASP Analysis Setpoint AV Allowable Value CCAS Containment Cooling Actuation Signal 0-E Corbustion Engineering CEA Control Element Assembly CEAC Control Elwent Assembly Calculator CEDM Control Element Drive Mechanism CFR Code of Federal Regulations CIAS Containment Isolation Actuation Signal CSAS Containment Spray Actuation Signal DBE Design Basis Event DNBR Departure from Nucleate Boiling Ratio EFAS Emergency Feedwater Actuation Signal ,

ESF Engineered Safety Features . .

ESFAS Engineered Safety Features Actuation System FSAR Final Safety Analysis Report IEEE Institute of Electrical and Electronics Engineers L T,0 Limiting Conditions for Operation LER Licensee Event Report LPD Local Power Density MSIS Main Steam Isolation Actuation Signal N.A. Not Applicable NRC Nuclear Regulatory Commission OL Operating License PPS Plant Protection System RCP Reactor Coolant Pump R.G. Regulatory Guide RPS Reactor Protection System l

RWT Refueling Water Tank SA Safety Analysis SCE Southern California Edison

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1408/caf-8 LIST OF ACRONYMS AND ABBREVIATIONS (Cont'd)

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SIAS Safety Injection Actuation Signal SONGS San ,0nofre Nuclear Generating Station STS Standard Technical Specifications I$6b Technical Specification e

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_ LIST OF DEFINITIONS 1

l Analysis Setpoint The Analysis Setpoint is the parameter value for the initiation of PPS actions assumed in the Safety Analysis to show acceptable consequences for Design Bacis Events.

Trip Setpoint The Trip Setpoint is the defined value in the Technical Specification which is the least conservative value wnich may be set into the protective equipmenc and still be consistent with the Safety Analysis setp 'nt assumptions.  ;

Allowable Value The Allowable Value is the defined value in the Technical Specification which is the letst conservative value that the Equipment Setpoint may have, when checked during the Functional Channel Check, and still be consistent with the Safety Analysis setpoint' assumptions.'

( i Equipment Setpoint The Equipment Setpoint is the actual value which is set into the protective equipment by the technician. The Equipment Setpoint

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must be set ' conservative or equrl to the Trip Setpoint value defined in the Technical Specification.

I Limiting Safety System Setting (LSSS)

The LSSS, which includes both the Trip Setpoint and Allowable Value, is the generic name for the Technical Specification set-point compliance values.

Initial Uncertainty The Initial Uncertainty is the uncertainty which must be taken into account if the protective equipment was required to respond immediately following calibration in the calibration environment.

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Periodic Test Uncertainty

.The Periodic Test Uncertainty is the uncertainty which must be

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taken into account if the equipment was required to respond at the end of the periodic surveillar.ce interval in the normal eniironment.

Total Instrument Channel Uncertainty The Total Instrument Channel Uncertainty is the combined total of all errors which must be taken into account if the equipment was

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required to respond at the end of the Periodic Surveillance interval under the limiting accident environment conditions.

Plant Protection System The Plant Protection System 'DPS) is made up of both the Reactor Protection System (RPS) and the Engineered Safety Features Actuation System (ESFAS). The RPS includes all equinment from the sensor

- up to and including the Reactor Trip Switc Jear. The ESFAS .

includes all equipment from the sensor to and including the ,

( Auxiliary Relay Cabinet.

Nominal Value The Nominal Value is the initial estimated value of the Trip Setpoint which is shown in the Safety Analysis Report (SAR) Chapter

7. The Nominal Value is based on estimated instrument uncertain-ties and anticipated environmental effects, as well as knowledge gained in efforts for previous plants.

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1.0 INTRODUCTION

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l.1 SCOPE By Reference'5.1 the Nuclear Regulatory Commission (NRC) requested specific setpoint relate,d dato for the San Onofre Nuclear Generating Station Units 2 & 3 (SONGS 2 & 3) Plant Protection System (PPS) from Southern California Edison (SCE). This document provides the requested information and also describes the Combuition Engineering (C-E) setpoint methodology used to determine SONGS PPS setpoints.

Section 1.2 provides the background which led up to the current setpoint related requirements and industry standards. Section 1.2 also describes the general requirements that were in effect for the PPS until approximately 1975, and tr.e more specific requirements on setpoint determination that have evolved since that time.

Section 2.0 describes the present C-E method of determin'ng pro.tection .

( system setpoints that is used to assure consistency with :urrent requirements and standards. Section 2.0 begins by explaining, in general, how setpoints are determined and how the different aspects of setpoint determination are l related to the Safety Analysis (SA) and to the plant Technical Specificaticns (Tech. Specs.). The remainder of Section 2.0 describes in more detail the specific components of the C-E explicit setpoint methodology.

Section 3.0 describes the equipment calibration and periodic test procedures which ensure that the equipment is operating in accordance with the assumptions and uncertainties used in the setpoint determination. This section ties the actual equipment operation to the setpoint calculation and is an integral part of demonstrating that plant operation will be consistent with the Safety Analysis. -

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Section 4.0 provides the specific data requested by Reference 5.1. The section begins with an explanation of the data in the tables and relates

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the data to the explanation of the C-E setpoint methodology. The remainder of Section 4.0 consists of tables which contain the requested information.

Section 5.0 lists the references referred to in this document.

1.2 BACKGROUND

On April 11, 1977 the NRC transmitted a letter to SCE concerning SONGS instrumentation setpoints (Reference 5.1). This letter stated that NRC reviet of facility operating experience indicates the need for additional information regarding the proper selection of instrumentation trip setpoint values. This conclusion was supported by the large number of Licensee Event Reports (LERs) received related to instrument setpoint drift beyond the limits permitted by the Technical Specifications. As a result, the letter requested explicit information concerning each Reactor Protection ,

System (RPS) and Engineered Safety Features Actuation System (ESFAS) trip .

( setpoint value.

NRC documents and industry standards have been d3veloped to provide require-ments and guidance concerning the proper selection of trip setpoint values.

For' example:

1. 10CFR50 (Reference 5.3) Section 50.36, Technical Specifications, specifies that Limiting Safety System Settings (LSSSs) are to be chosen so that automatic protective action will correct abnormal situations before a safety limit is exceeded.
2. 10CFR50 (Reference 5.3) Section 50.55, Codes and Standards, specifies that protection systems shall meet the requirements of IEEE 279-1971 (Reference 5.4).

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3. 10CFR50 (Reference 5.3) Appendix A, Criterion 20, Protection

( System Functions, specifies that the protection system shall function automatically to assure acceptab7e consequences during postulated events.

4. IEEE,279-1971 (Reference 5.4) specifies that the protection system shall automatically initiate protective action whenever monitored conditions reach preset levels.

These requirements in general, apply to both the F.PS and the ESFAS, which collectively make up the Plant Protection System (PPS). These requirements state that protection systems (and their setpoints) shall be designed to assure their proper operation (at the prcper setpoint) during events that require protective action. Recent NPC documents which have provided setpoint guidance include:

1. The NRC issued Standard Technical Specifications (STS) (Reference .

5.5) which call for specific accounting of instrument. drift in -

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the setpoint determination process.

2. R.G.l.105 (Referer.ce 5.6) includes specific requirements on setpoint margin, drift allowance, uncertainty components and l

documentation of setpoint methodology.

3. The Advisory Committee on Reactor Safeguards (ACRS) transcript on Item 13 (Reference 5.7) discusses two methods of setpoint deter-mination the " generalized" method and the " explicit' method.

The " generalized" method includes a bulk uncertainty thtt charac-terizes a typical measurement channel. On the other hand, the

" explicit" method includes an explir.it treatment of drift, instrument error, calibration error and environmental error. As pointed nut in the transcript, the NRC is moving toward requiring that the explicit method be used for setpoint determination as a prerequisite I for receiving an Operating License.

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.1408/caf-14 4 In Reference 5.1, the NRC has recently requested more explicit

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data from SCE concerning setpoint methodology.

The Combustion Engineering RPS and ESFAS is designed to meet all of the above requirements. The methodology employed to calculate equipment satpoints is consistent with these requirements and is an " explicit" method ,

as discussed in References 5.6 and 5.7 This document describes the C-E " explicit" method of setpoint determination.

It also provides the specific information requested of SCE by Reference 5.1. Th's inforaation is contained in Tables 1-7 at the end of the report.

Section 4.0 describes how the information is compiled in the Tables and provides a one-to-one correlation between the specific information requested in Reference 5.1 and the data in the Tables.

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. 2.0 SETPOINT METHODOLOGY

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2.1 BASIC DESCRIPTION The SONGS Plant Protection System consists of both RPS and ESFAS trip functions.

The RPS includes 14 trip functions, two which are generated by the CPC digital computer. Both the CPC trip paths and the non-CPC trip paths include sources of uncertainty and drift. The C-E " explicit" method of calcultting setpoints is used to ensure that al. identified equipment uncertainties are accommodated.

Section 2.5 describes the C-E setpoint method for CPC generated trips, the remaining portions of Section 2.0 discuss the setpoint methodoiogy applicchle to the non-CPC portion of the RPS and all the ESFAS trips.

Figure 1 describes the C-E PPS Setpoint methodology in block diagram form.

, The Setpoint methodology begins when a Safety Analysis is performed to show that the consequences of Design Basis Events (DBEs) will be acceptable. ,

The Safety Analysis assumes protective action is initiated when.the process .

( variables reach established values. The values assumed in the Safety Analysis are defined as Analysis Setpoints (ASP).

A detailed equipment error calculation which combines the individual dncertainty components into a Total Instrument Channel Uncertainty is performed for each PPS function. This Total Instrument Channel Uncertainty and the Analysis Setpoint are used to establish the Trip Setpoint. The Trip Setpoint is set in a conservative direction from the Analysis Setpoint a distance representing the Total Instrument Channel Uncertainty. The Trip Setpoint becomes part of the plant Technical Specifications (Reference 5.2). ,

As an integral part of the equipment error calculation, a number is determined which represents the expected measurable equipment drift over a specified period between calibrations. This value is the Periodic Test Uncertainty. An Allowable

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, 1408/cef-16 Value is defined by moving from the Trip Setpoint toward the Analysis Setpoint

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be consistent with the Safety Analysis.

Thus the C-E setpoint methodology results in a Trip Setpoint and an Allowable Value which, assuming the equipment is operated as designed, assure that protective action will be initiated conservatively relative to the Analysis Setpoint used in the Safety Analysis. The Trip Setpoint and Allowable Value together make up the Limiting Safety System Setting (LSSS) required in the Technical Specifications.

The remainder of Section 2.0 discusses in greater detail the specific components of the C-E " explicit" setpoint methodology.

2.2 ANALYSIS SETPOINT ,

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As a btsic requirement, setpoints must be chosen to (1) ensure initiation of requ red protective action to show seceptable consequences for safety related Design Basis Events (DBEs) and, (2) to ensure that performance related DBEs can be accommodated without initiating protective actian.

Refer to Figure 2 during the discussion on determining Analysis Setpoints.

As an initial step in setpoint determination the equipment errors for each trip function are estimated using known equipment characteristics, the l

anticipated envirer. ental effects, and knowledge gained in previous efforts l

for different plants. Additionally, the operating ranges for the measured parameters are determined for normal steady-state conditions and during performance related DBEs. These are combined to form the basis for the initial setpoint.

This setpoint is called the Nominal Value and represents the approximate value of the expected final setpoint. The Nominal Value is used in the Preliminary Safety Analysis Report (PSAR). Before the final Safety Analysis

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is completed and incorporated into the Final Safety Analysis Report (FSAR) 2-2

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1408/caf-17 the Nominal Value is adjusted, again considering the estimated total equipment I error, to result in a value that represents the expected most limiting point at which a protective action would be initiated if the equipment setpoint was set at the Nominal Value. This resulting value is the Analysis Setpoint which is input to the Safety Analysis. Analysis Setpoints are, in some cases, results of parametric stydies conducted until a setpoint is determined which will result in an acceptable Safety Analysis and acceptable plant performance.

In the Safety Analysis, the Analysis Setpoint is the value of the measured parameter at the measurement point which is assumed to initiate protection system actuation. The Safety Analysis is described in the Final Safety Analysis Report (FSAR) and is part of the documentation required to receive an Operating License. Some events analyzed in the Safety Analysis result in a more severe environment for protection system equipment than other events. As a result the expected total equipment error can be different for different events (i.e. , event specific). Therefore, a trip function .

can have different Analysis Setpoints for different design basis events. -

g The final Analysis Setpoints used in the Safety Analysis are then used in the setpoint. calculation to determine Trip Setpoints and Allowable Values as described in subsequent sections of this report.

2.3 EQUIPMENT ERRORS 2.3.1 General Good engineering practice and current setpoint requirements dictate that all factors which can affect the operation of equipment be considered when determining errors in the setpoint calculation. In the C-E setpoint methodo-logy, each error component that can have an impact on equipment performance is determined separately and then the individual errors are combined by a statistically valid method to arrive at a total equipment uncertainty. The individual errors are plant-specific and equipment-specific and thus must be determined for each plant on a case-by-cese basis. The following paragraphs

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1. PPS Cabinet Initial Unc2rtainty;

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2. PPS Cabinet Periodic Test Uncertainty;
3. Process Equipment Initial Uncertainty;
4. Process Equipment Periodic Test Uncertainty;
5. Accident Environment Error;
6. Process Error;
7. Dynamic Allowance.

For means of setpoint calculation, tne PPS is divided into two major regions (Figure 3.) The first region is the process equipment. This consists of the sensor, transmitter, power supply and signal processing equipment - all ,

equipment up to the PPS cabinet. The second region is the PPS cabinet

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itself. Each of these regions provide individual error components.

2.3.2 Individual Errors 2.3.2.1 PPS Cabinet Initial Uncertainty The PPS Cabinet Initial Uncertainty is the uncertainty inherent in the equipment and calibration of the PPS cabinet instrumentation and represents the error that would have to be accounted for if the instrumentation was required for protective action immediately after the calibration procedure was performed. This uncertainty is determined for the specific equipment

- installed in the PPS cabinet from information supplied by the manufacturer and actual calibration requirements of the equipment.

2.3.2.2 PPS Cabinet Periodic Test Uncertainty

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The PPS Cabinet Periodic Test Uncertainty accounts for the expected drift of the PPS cabinet equipment over the period from when the setpoint was set 2-4

1408/caf-19 until the monthly Channel Functional Check is performed to check the setpoint.

I When determining this uncertainty, the following aspects are considered:

the error associated with setting and checking the setpoint, errors because of the differ,ence in PPS cabinet environment at the time the setpoint is checked and the environment when the setpoint was set, and errors due to anticipated dri.ft of the PPS. cabinet equipment. These component errers are combined to determine the PP5 Cabinet Periodic Test Uncertainty in a manner similar to that described in'section 2.3.3 for determining total equipment errors. The PPS Cabinet Periodic Test Uncertainty is calcuicted using information supplied by the equipment manufacturer and from actual testing of the equipment.

2.3.2.3 Process Equipment Initial Uncertainty This uncertainty is analogoos to the PPS Cabinet Initial Uncertainty but applies to tl'e process equipment as shown on l'igure 3, instead of the PPS cabinet. This is the error inherent in the calibration and operation of .

the process equipment and represents the error that would have to be accounted

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for if the equipment was required for protective action immediately after the calibration procedure was performed. As with the previous errors, the Process Equipment Initial Uncertainty is determined for the specific equip-ment installed at the plant from information supplied by the manufacturer and actual calibration req irements on the equipment.

2.3.2.4 Process Equipment Periodic Test Uncertainty The Process Equipment Periodic Test Uncert inty is analogous to the PPS cabinet Pericdic Test Uncertainty but appl, to the process equipment.

This uncertainty accounts for the expected measurable drift of the process equipment during the time between channel calibrations, which are performed I

as a minimum every 18 months as required by the plant Technical Specifications (Reference 5.2). The same aspects are considered when c&lculating this error as are considered when determining the PPS Cabinet Periodic Test ,

Uncertainty riescribed above and the components are combined in a similar l

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. 1408/caf-20 2.3.2.5 Accident Environment Error

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During certain design basis events, combinations of atmospheric changes and seismic events are considered to occur simultaneously. These changes in environment introduce additional errors in the process equipment which must be considered in the overall setpoint calculation. Examples of specific environmental effects on equipnent error which are considered are: temp-erature effects, pressure effects, reference leg effects, seismic effects, and radiation effects. The individual accident environment errors are combined in a manner similar to that used to calculate total equipment errors described in section 2.3.3. The environment considered when determin-

' ing these errors is the most detrimental realistic environment calculated or postulated to exist up to the time of the required Reactor Trip or Engineered Safety features (ESF) actuation.

This environment may be different for different events analyzed. In most cases, for setpoint calculation, the accident environment error calculation ,

for process equipment uses the environmental conditions that result in the .

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largest errors, thus adding additional conservativism (i.e. , greater margin) for the events with smaller errors. In some cases, however, the accident environment errors for some events are much larger then those for events with little or no containment environment change. In these cases, specific errors are calculated for different events. The event specific errors are then used in calculating total equipment errors which also become event specific.

2.3.2.6 Process Error The Process Error accounts for the uncertainty in the value of the process parameter (e.g., neutron flux power, temperature variation) at the sensor. In most cases the errors which exist between the actual process parameter and the value at the sensor are incorporated into the Safety Analysis instead of beccming part of the setpoint calculation. When included as part c'. the setpoint calculation, the procers errors are combined with the other equipment errors to determine the Total Instrument Channel Uncertainty.

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1408/ mad - 21 2.3.2.7 Dynamic Allowance I

As part of the Safety Analysis, a time delay is used to account for the delays inherent in the PPS equipment. For the RPS, this time delay re-presents the' time from when the process value at the sensor reaches the

. trip point to the time when the Reactor Trip Switchgear is de-energized.

For the ESFAS this time delay represents the time from when the process value at the sensor reaches the actuation point to when the actuation signal is output from the Auxiliary Relay Cabinet. When the actual PPS l of the various components are determined equipment is tested, time de.ays and verified. The total time delay is then determined.

In certain cases, if it is determined that the actual delay time for the equipment is longer tha7 the delay time used in the Safety Analysis, a Dynamic Allowance may be incorporated into the setpoint to compensate for this time response difference. To assure that a protective action occurs at or before the time assumed in the Safety Analysis, the Trip Setpoint is '

altered in a conservative direction by the Dynamic Allowance to compensate ,

I for the sensor response characteristics.

2.3.3 Total Instrument Channel Uncertainty dftertheindividualerrorcomponentshavebeendetermined,theyarecombined to arrive at a Total Instrument Channel Uncertainty which is used in calculating the Trip Setpoint. Each individual error can consist of both random and non-random components. Random errors are errors of uncertain algebraic sign (+or-). Non-random errors are errors having a known sign. The resulting total error is a statistical combination of a random error component and a non-random component. The Total Instrument Channel Un-certainty represents the maximum uncertainty calculated that could occur at any time during the periodic surveillance interval for the limiting event for which the function is required to operate. In the case of different

- accident environrent errors, for different events, event specific total equipment errors are calculated for each function. The event specific Total Instrument Channel Uncertainties are used to determine the Trip Setpoints.

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1408/caf-22 2.4 SETPOINT DETERMINATION I

2.4.1 General The plant Technical Specifications (Reference 5.2 ) require Trip Setpoints and Allowable ifalues for PPS functiona. The Trip Setpoints and Allowable Values are determined using the Analysis Setpoint (Sec. 2.2) and the Total Instrument Channel Uncertainties (Sec. 2.3). The following sections describe the method used for calculating Trip Setpoints and Allowable Values.

2.4.2 Trip Setpoint Section 2.3.3 discusses how the Total Instrument Channel Uncertainty is determined for each PPS function. This error represents the total un-certainty which must be accommodated and accounts for all the individual errors which can affect the accuracy of the equipment being used. To accomodate these errors in the setpoint calculations, the Trip Setpoint is ,

established in a conservative direction from the Analysis Setpo. int by the ,

amount of the Total Instrument Channel Uncertainty. When different totai equipment errors and different Analysis Setpoints are determined for dif-ferent analyzed events, the event specific Trip Setpoints are set in a conservative direction by the correspond'ng event specific Total Instrument Channel Uncertainties. The most conservative resulting value is then used as the Trip Setpoint.

This method assures a conservative setpoint in all cases. Figure 4 is a representation of Trip Setpoint calculations where different events are analyzed separately.

The calculated Trip Setpoint for each PPS function becomes part of the plant Technical Specifications and represents the least conserv2tive value that may be set into the equipment during initial calibration. To be consistent with the STS format the Trip Setpoints shown in the plant Technical Specifications are prefaced with a < or 1, depending on whether the setpoint

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1408/ mad - 23 is above or below the normal operating range, respectively. This assures set-(

ting the Equipment Setpoint, the actual value set into the bistable, equal to or more conservative than the Trip Setpoint values s'hown in the Technical Specifi-cations.

2.4.3 Allowable Value The PPS Cabinet Periodic Test Uncertainty represents the maximum anticipated me'surable drift of the PPS cabinet equipment during the specified period of time between calibrations. (Section2.3.2.2) This uncertainty is used when t'lculating the Allowable Value. The Allowable Value is defined by moving from the Trip Setpoint toward the Analysis Setpoint by the amount calculated for the PPS Cabinet Periodic Test Uncertainty. The resulting Allowable Values are listed in the plant Technical Specificatior.s (Reference 5.2). The Technical Specifications require that if, upon checking a setpoint, it is found to be less conserva.tive tnan the Allowable Value, the channel must be declared inoperable, specific action must be taken and the Equipment .

Setpoint must be reset. , ,

By calculating the Allowable Value as described above the problem of anticipated equipment drift causing spurious trips during normal operations, or causing setpoint drift which is inconsistent with the Safety Analysis, is virtually eliminated.

2.4.4 Technical Specifications For ea.h PPS function, the Trip Setpoint and Allowable Value which have been calculated to assure that the equipment will operate as assumed in the Safety Analysis are incorporated into the plant Technical Specifications.

Th'ese two values makt up the Limiting Safety System Setting (LSSS) required by the Technical Specifications.

As part of the setpoint calculation used to arrive at the Trip Setpoints and Allowable Values, certain assumptions were made. These include: the accuracy of the equipment used; the calibration intervals; the method of

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calibration; and other equipment characteristics. Section 3.0 explains hcw

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these assumptions are incorporated into the setpoint calculation.

2.5 CORE PROTECTION CALCULATOR SETPOINTS 2.5.1 General The SONGS Reactor Protection System uses a Core Protection Calculator (CPC) to generate two of the fourteen reactor trip signals. For the purpose of this report, when the Core Protection Calculator is referred to, it includes the Control Element Assembly Calculator (CEAC) as part of the CPC system.

The CPC inputs and trip functions are shown in Figure 5.

The CPC is a digital calculator, and as such requires a different method than the other PPS trips to ensure that all equipment uncertainties are accommodated in the decision to initiate a reactor trip. (See Sec. 3.5.1)

Methods of incorporating uncertainty compensation into the CPC have been addressed in detail in documents previously submitted to the NRQ. (Referent.es k 5.8,5.9). The following discussion summarizes the information presented in these documents.

2.5.2 CPC Uncertainty Components Calculations performed by the CPCs are modified to account for the following uncertainties and allowances:

1. Heasurement uncertainties;
2. Algorithm modelling uncertainties;
3. Algorithm constants uncertainties;
4. CPC processing uncertainty;
5. Static allowances; 2-10

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6. Dynaaic allowances.

( I A general discussion of each of the listed items is given below.

2.5.2.1 Measurement Uncertainties Sensor and measurement channel uncertainties for the CPC measured inputs make up the CPC measurement uncertainties. As shown in Figure 5, the CPC measured inputs include:

1. Reactor coolant cold leg temperature;
2. Reactor coolant hot leg temperature;
3. Pressurizer pressure;
4. Reactor coolant pump (RCP) rotational speed; ,
5. Ex-core detector neutron flux;
6. CEA position.

A measurement uncertainty is calculated for each of the above CPC inputs.

Section 2.5.3 describes the method used to factor the CPC measurement uncertainties into the CPC algorithms. The uncertainties calculated for the CPC measured inputs are based on manufacturer's instrument specifications, type testing, calculations and previous operating experience. The specific uncertainties calculated contain allowances for all components in the measurement channel including sensor, transmitter, power supply, dropping resistor, multiplexer ar.d analog to digital converter (A/D).

Figure 6 shows in block diagram form the CPC in relation ;a the SONGS PPS and those portions of the PPS that are considered when determining CPC measurement uncertainties.

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1408/caf-26 For each component in the measurement channel, instrument linearity, repeat-( ability, environmental effects, and drift between calibration periods are considered in the calculation of measunement uncertainties. The resulting measurement channel uncertainty is analogout to the uncertainty that would be obtained for the non-CPC portion of the RPS (described in Section 2.3) if the following uncertainties were combined:

1. Process Equipment Initial Unce-tainty;
2. Process Equipment Periodic Test Uncertainty;
3. Accident Environment Error;
4. Process Error.

The method of combining the individual components to arrive at the measurement channel uncertainty is similar to the method described in Section 2.3.3. .

(

The resulting CPC measurement uncertainty includes a random component and a non-random component.

2.5.2.2 Algorithm Modelling Uncertainties Algorithm modelling uncertainties address the accuracy with which the CPC algorithms replicate the results of design codes, "best estimate" measurements and/or "best estimate" calculations.

2.5.2.3 Algorithm Constants Uncertainties Algorithm constants uncertainties address the accuracy of the measurements and/or calculations used to.obtain tre CPC algorithm constants. This type of uncertainty depends upon both the accuracy of the instruments used in the measurements as well as the technique used to process the measurements.

Algorithm constant uncertainties can consist of both random and non-random components.

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2-12

m 1408/caf-27 2.5.2.4 CPC Processing Uncertainty

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The CPC processing uncertainty is attributable to the effects that sealing, round-off and bit manipulation nave on the CPC computed result. Testing of the CPCs and CPC calculations provide the information needed to determine this uncertainty. Comparison of actual CPC response to the results obtained using the CPC algorithm with the higher resolution computino facility used in the design process and the Safety Analysis provides a mechar. ism for quantifying and characterizing the processing uncertainty.

2.5.2.5 Static Allowances Static al'lowances account for the effect on the margin to fuel design limits of (1) variations in parameters not monitored by the CPCs, and (2) allowed variations (action thresholds or deadbands) in the pirameters monitored by the CPCs. The only parameter that falls into the first category is the azimuthal power tilt magnitude. An example of a parameter in the ,

second category is the deadbands on CEA deviation provided in the CPC. .

2.5.2.6 Dynamic Allowances pynamic aliowances account for the time delays associated with the following:

1. CPC sensor delays;
2. CPC sampling intervals; i 3. CPC processing times; l
4. RPS trip logic delays; t

l 5. CEA holding coil decay times; i

6. CEA insertion times; l

l l

l I

l 2-13 I

i

l 1408/caf-28

7. Transient delays associated with the heat flux and stored energy

( response following CEA insertion. ,

Accounting fcr these delays in the decision to initiate a Low DNBR or High Local Power Density (LPD) reactor trip ensures that the transients analyzed in the Safety Analysis will be terminated before the actual fuel design limits are exceeded.

2.5.3 Accommodatino CPC Uncertainties 2.5.3.1 General Method The CPCs are designed with the capability of accommadating uncertainties in a variety of ways with the choice being dependent upon the nature of the uncertainty component. Measurements can be biased prior to use in calculations to account for uncertainties and/or allowances; calculated results can be individually modified; or selecteo calculated values can be modified to ,

account for the effect of all of the uncertainty components on the final .

g trip comparison. The optimum method of accommodating uncertainties in the CPC will simultaneously ensure conservatism and maximize operating flexibility.

The method of accommodating CPC uncertainties for the SONGS Reactor Protection System involves determining constants which then become part of the CPC program. These constants result from combining the individual uncertainties discussed in Section 2.5.2 in a manner which ensures all uncertaiscies are accommodated. The combination of individual uncertainties to arrive at the CPC uncertainty adjustment constants is similar to the method described in Section 2.3.3 for combining errors in the non-CPC portion of the protection system.

Separate constants are determined and used for the DNBR and LPD trip calcula-tions. Tha following sections discuss the constants used in the DNBR and LPD calculations.

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2-14

,1408/ mad-29 2.5.3.2 DNBR Uncertainty Constants I There are three uncertainty constants used in the DNBR calculation which together ensure a low DNBR trip response that is conservative relative to the Safety Analysis. These are:

1. Uncer.tainty biases for power used in the DNBR calculation (BERR2,BERRO)
2. Power uncertainty factor used in the DNBR calculation (BERRl)*

2.5.3.2.1 Uncertainty Biases for Power Used in the DNBR Calculations (UERR2, BERRO}

The uncertainty biases for power used in the DNBR calculation account for the uncertainties inherent in the inputs to the power calculation in the CPC. These include the power calibration uncertainty and the dynamic uncertainty in both the neutron flux power (BERR2) and the thermal power These uncertainties are measurement uncertainties and dynamic (BERR0). '

allowances (as discussed in Sections 2.5.2.1 and 2.5.2.6, respectively).

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The uncertainty biases for power used in the DNBR calculation are added to the calculated power level as:

POWER "

THERMAL ODT + OERR0 POWER "

FLUX ONF + BERR2 where B = Calculated thermal power.

DT B = Calculated neutron flux power.

NF Adjusted thermal power. ,

POWERTHERMAL =

POWER = Adjusted neutron flux power.

FLUX These adjusted powers are used as input to the compensi; ion algorithms.

( The resulting " compensated" powers are auctioneered to give POWERCOMP' 2-15

1408/aad - 30 g 2.5.3.2.2 Power Uncertainty Factor Used in the DNBR Calculation (BERRI)

This factor a,ccounts for the uncertainties not accounted for by the previous constants. The r..athod of combining the individual uncertainty components to determine the actual values used for this constant is similar to the method described in Section 2.3.3 of this report. The compensated power level corrected for power measurement uncertainties is then multiplied by the appropriate constants to result in the power level used in the DNBR calculation, as:

POWER =

DNB ADJ POWERc.0MP'0 ERR 1

. Where POWER = Corrected power level used in the DNBR calcu-DNB ADJ lation B = Power uncertainty factor used in th_ DNBR ,

ERR 1 ca!culation. . .

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2.5.3.3 Local Power Density Uncertainty Constants There are two uncertainty constants used in the LPD calculation which, together, ensure a high LPD trip response that is ccnservative relative to the Safety Analysis. These are:

1. Uncertainty bias for power used in the LPD calculation (BERR4)
2. Power uncertainty factor used in the LPD calculation (BERR3}

4 2-16

1408/ mad-31 2.5.3.3.1 Uncertainty Bias for Power Used in the LPD Calculation (BERR4)

I The uncertainty biases for power used in the LPD calculation accounts for the uncertainties inherent in the power measurement process inpJt to the CPC.

This includes the power calibration uncertainty and t;:e dynamic uncertainty in both the neutron flux power and the thermal power. These uncertainties are measurement uncertainties and dynamic allowances (as discussed in Sections 2.5.2.1 and 2.5.2.6, respectively). The uncorrected power level used in the LPD calculation is the same as that used in the DNBR calculation and the uncertainty components of the uncertainty bias for power used in the LPD calculation are identical to the components of the uncertainty bias for power used in the DNBR calculation. The uncertainty bias for power used in the LPD calculation is added to the calculated power level as:

POWER =

LPD POWERCALC + BERR4 where POWERLPD = Power level input to the LPD calculation corrected for power measurement uncertainties - ~

4 POWERCALC =  ? wer level calculated from neutron flux or thermal measurements B

ERR 4

= Uncertainty bias for power used in the LPD calcula-tion.

2.5.3.3.2 Power Uncertainty Factor Used in the LPD Calculation (BERR3)

The power uncertainty factor used in the LPD calculation accounts for the uncertainties not accounted for by the .LPD power measurement. This is analogous to the DNBR constant B described in Section 2.5.3.2.3. The ERR 1 '

method of combining the individual uncertainty components to determine the constant is similar to the method described in Section 2.3.3 of this report.

The power level already corre:ted for power measurement uncertainties is then multiplied by the power uncertainty factor used in the LPD calculation

( to result in the power level used in the LPD calculation, as:

2-17

1408/caf-32 LPD ADJ LPD .BERR3 where POWER LPD ADJ

= Corrected power level used in the LPD calcula-tion B

ERR 3

= Power uncertainty factor used in the LPD calculation.

OR:

=

POWER LPD ADJ ( ERCALC

  • OERR4) .BERR3 2.5.3.4 Technical Specifications As showr; in the Technical Specifications (Reference 5.2) and in Table 5 of this report, the Analysis Setpoint, Trip Setpoint aid Allowable Value for the Low DNGR trip are identical. This is also true for the High Local I Power Density Trip function. As has been discussed in Section 2.5.3, all uncertainties in the CPC system, including dynamic responses and equipment drift are accommodated as correction constants in the calculation of DNBR and Local Power Density. This ensures that when the calculated DNBR or LPD reaches its respective Trip Setpoint value and the RPS sends out a reactor trip signa'!, tSe response of the protection system will provide protection during the Design Basir. Events analyzed. Because of this method of accom-modating uncertainties in the CPCs, for each CPC trip function, the Trip Setpo1nt is identical to the Nnalysis Setpoint used in the Sa,ety Analysis.

Also, the CPC, being a digital computer system, is not subject to setpoint drift like the non-CPC analog trip functions. Thus no allowance for setpoint drift is required and the Trip Setpoint and Allowable Value are identical for each CPC trip function.

2.6 RATE LIMITED VARIABLE SF.TPOINTS Ihis section describes the uncertainties applied to the RPS trip used to mitigate the RCP sheared shaft event; as c'escribed in Section 7.2 of the FSAR, and will be provided by July, 198l.

T-18 .

. ,1408/caf-33 3.0 EQUIPMENT CALIBRATION

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3.1 BASIC DESCRIPTION The C-E " explicit" setpoint methodology determines Trip Setpoints and Allowable Values for the PPS trip functions. When the respoint calculation is performed, it is assumed the equipment will be maintained and will operate in accordance with the Technical Specification requirements. These requirements include: surveillance requirements on how often equipment calibration must be performed; setpoint data which specifies the value ti.2 equipment is to be set to and the value allowed during scheduled testing; and re@onse time requirements on how rapidly the equipment must operate.

The C-E setpoint procedures provide an input to the plant Technical Specifi-cations to ensure that the Plant Protection System operational requirements are ir; accordance with the assumptions and requirements used in the setpoint calculations.

Additional assumptions are made about the actual operation of the PPS .

I equipment which are not directly reflected in the Technical Specifications.

These include such things as accuracy of the instrcments used in the calibration, and the environmental conditions during calibration. To ensure that these assumptions are validated, Combustion Engineering supplies Southern California

, Edison with PPS Calibration and Testing Data and Guidelines. SCE incorporates this information into their calibration and testing procedures.

This system ensures the equipment is operated in a manner such that the setpoint calculation remains valid. The equipment will then perform conservatively with respect to the Safety Analysis.

3.2 SETPOINT DETERMINATION ASSUMPTIONS An integral part of the setpoint determination process is determining the individual error contributions that must be considered in calculating a total equipment error.

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. 1408/caf-34 To determine these individual error comp;nents, specific data is obtained g

such as: inherent equipment accuracy from the manufacturer and equipment testing; equipment response du'*ing transients; equipment response with environment changes; equipment drift with time; and environment response during Design Basis Evente. However, the data obtained is not sufficient, in itself, to enable the error components to be determined. Ctrtain assumptions must be made concerning the operation, testing and calibration of the actual equipment installed at the plant.

As part of the calculation process, these specific assumptions are documented.

This is the first step in ensuring that these assu,cptions are verified and thus ensuring that the setpoint calculations remain valid.

3.3 TECHNICAL SPECIFICATIONS The major method of ensuring the assumptions made during the setpoint calculations process are valid is via the plant Technical Specifications ,

(Reference 5.2). These Technical Specifications are requiremen,ts imposed .

I by the NRC on the operation of the plant which must be met to continue operation. The Limiting Conditions for Operation (LCO) and the Surveillance Requirements for the Reactor Protective Instrumentation are Sections 3.3.1 and 4.3.1, and for the ESFAS Instrumentation these are Sections 3.3.2 and 4.3.2, of the technical specifications. Included in these sections are requirements for:

1. The frequency that the instrumentation is to be calibrated and the types of testing and calibration to be performed at these required intervals;
2. The frequency that the instrumentation response time is to be verified and the maximum acceptable response times during testing.

These requirements correspond to certain assumptions made and documented during the setpoint calculation. As one of the final steps in the setpoint calculation process, the specific data input to these technical specifications

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is provided consistent with the corresponding assumptions.

3-2

1408/caf-35 3.4 CALIBRATION GUID'dLINES

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The final method of ensuring that the assumptions made in the setpoint calculation remain valid during plant operation is via calibration guidelines.

These calibration guidelines are prepared by Cembustion Engineering as part of the setpoint calculation process t.nd are transmitted to Southern California Edison. SCE then incorporates these guidelines into their detailed operating, testing and calibrating procedures.

Included in the calibration guidelines are the assumptions made in the setpoint calculation not specifically verified by the Technical Specification requirements. Also included in the calibration guidelines are the equipment voltages corresponding to the Trip Setpoints and Allowable Values. This assists the plant staff in ensuring the equipment is calibrated and tested correctly because the Technical Specificrtion data is in measured parameter values (e.g., psia, % of rated thermal power) and the actual equipment values are voltages. ,

I Thus, the combination of incorporating the calibration guidelines into plant proceJures and operating in accordance with the plant Technical Specifications ensures that the assumptions made in the setpoint calculations remain valid during the operation of the plant.

3.5 CPC CALIBRATION 3.5.1 General As previously described, the CPC is a digital computer system. It processes measured input parameters and generates a low DNBR or a High Local Power Density reactor trip signal when the calculated values reach a predetermined setpoint. The difference between these trip functions and the other trip functions in the Flant Protection System is that the decision to initiate a reactor trip is performed by a digital computer in the CPCs instead of by reaching a predetermined value in an analog bistable. For calibration and testing purposes the CPC trip channel is divided into two parts as shown in

(

3-3

, ,1408/ mad-36 .

Figure 6. The first part is the process equipment which provides the input signals to the CPC computer and the second part is the CPC computer system I

itself. Calibration of each of these parts is discussed in the following sections.

3.5.2 CPC Process.Eauipment Calibration The CPC process equipment includes all equipment in the chain from the sensor up to and including the analog to digital converter (A/0) which provides the digital measurement signal to the CPC (see Figure 6). Except for the A/D, this is identical to the non-CPC portion of the protection system previously discussed. The A/D is treated in a manner similar to the rest of the process equipment in ti.a setpoint calculatien process. All uncertainties are considered which can affect the accuracy of the A/D; these uncertaintias are combined to determine an A/D total uncertainty; and the A/D total uncertainty is combined with the other process measurement uncertainties when determining the total process measurement uncertainty.

As with the rest of the process equipment, certain assumptions must be made , '

( about the operation, calibration, and testing of the A/D when determining its uncertainty. These assumptions are verified during plant operation to ensure the setpoint calculation remains valid.

Thus the entire process equipment calibration procedure for the CPC inputs is identical to the procedures for the non-CPC process equipment.

3.5.3 CPC Computer System Calibration The remainder of the CPC portion of the protection system is the CPC computer system itself. The CPC digital computer is different from the rest of the RPS trip decision logic in that the CPC trip setpoint is not subject to drift and thus drift was not considered as part of the CPC uncertainty calculation discussed in Section 2.5. There are however numerous similar-ities between the CPC and non-CPC portions of the protection system concern-ing equipment calibration; and hence, the majority of the preceding sections also apply to the CPCs.

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3-4

1408/caf-37 When determining equipment uncertainties for the CPC, certain assurnptions I are made that require verification to ensure the CPC method of accomodating uncertainties remains vclid. As with the rest of the protection system these assumptier.: are documented during the design process. It is then ensured t'.at the Technical Specificatbns include requirements that, when met, wiP, verify these assumptions. This in turn ensures CPC operation consistent with setpoint requirements.

Because the CPC is a digital computer the algorithm is also not subject to drift. As such the monthly Channel Functional Test required by the technical specift;ations is different from the tests performed on non-CPC channels.

For the CPC, frctional testing involves such tasks as verifying, one-for-one, that the informatioa stored in protected memory agrees with the data on the test c'isc, and using test inputs to check the CPC outputs fot cor' rectness.

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3-5

W

. 1408/ctf-38 4.0 DETAILED SETPOINT DATA

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4.1 NRC REQUEST On April 11,'1977, the NRC sent a letter on " Instrument Trip Setpoint Values - San Onofre Nuclear Generating Station - Units 2 and 3" to SCE (Reference 5.1).

This letter stated that NRC review of facility operating experience indicates the need for additional information regarding the proper selection of instrumentation trip setpoint values. This conclusion is supported, the letter states, by the large number of Licensee Event Reports (LERs) received by the NRC related to instrument setpoint drift beyond the limits permitted by the facility Technical Specifications. As a result, the NRC requested explicit information concerning each RPS and ESFAS instrumentation channel trip setpoint value. The specific information requested was:

. 1. The technical specification trip setpoint value; ,

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2. The teranical specification allowable value;
3. The instrument drift assumed to occur during the interval between technical specification surveillance tests;
4. The components of the cumulative instrument bias;
5. The minimum margin between the technical specification trip setpoint and the trip value assumed in the accident analysis.

The .information requested is purely numerical data. This report has explained the Combustion Engineering " explicit" setpoint methodology so that the data, will be more easily understood. Tabies 1 - 7 contain the required data. The remainder of Section 4.0 is an explanation of these tables and ties the data in the cables with the setpoint methodology previously discussed.

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4-1

. 1408/caf-39 4.2 EXPLANATION OF TABLES

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4.2.1 General Tables 1 - 7 contain explicit data on the RPS and ESFAS used in the equipment setpoint determination process. This provides the information requested in Reference 5.1. Tables 1 - 4 contain information for the non-CPC portion of the Plant Protection System and Tables 5 - 7 contain the requested information for the CPC portion.

Many values given in the tables contain both a random (+) and a non-random

(+) or (-) component.

The following sections 4.2.2 - 4.2.6 provide an explanation of the columns of data contained in Tables 1 - 7. Section 4.2.7 discusses additional items by PPS function where further clarification is helpful.

4.2.2 Table 1 . -

Table 1 contains the Trip Setpoint, Allowable Value and the Drift Allowance for each discussed PPS function. The Trip Setpoint is the least conservative value which may be set into the PPS equipment at calibration to ensure protective action before the Analysis Setpoint is exceeded. The Trip Setpoint corresponds to the data requests in item 1 of the NRC letter. (see Section 4.1). The Allowable Value is the limit on the Trip Setpoint at any time during normal plant operation and is checked during the monthly Channel Functional Test as required by the technical specifications. Operation with an Equipment setpoir; conservative with respect to the Allowable Value is necessary to assure :ha equipment will operate as assumed in the Safety Analysis. The Allowable Value data presented corresponds to item 2 of the NRC request. The third column l

corresponds to item 3 of the NRC request. The PPS Cabinet Periodic Test Un-l certainty represents the allowance which must be made for measurable drift in the PPS Cabinet. This allowance represents the time dependent drift and the measurement and equipment uncertainties inherent in verifying that the anti-

, ( cipated drift does not cause the Equipment Setpoint to exceed the Allowable j Value between surveillance intervals.

4-2

1408/ mad-40 4.2.3 Tables 2 and 3

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Tables 2 and 3 contain the values for the components used in the total equipment error calculation. This corresponds to item 4 of the NRC request.

A discussion of each of these components is contained in Section 2.3 of this report.

Table 2 contains PPS cabinet and PPS measurement channel data. For each equipment area the uncertainty calculated for initial and periodic testing is listed. The Initial Uncertainty accounts for basic inaccuracies in the equipment used during calibration and in the equipment being calibrated.

The periodic testing procedure uses the same equipment as during calibration.

Therefore, the Initial Uncertainty is included in the calculation of the Periodic Test Uncertainty in addition to the other components, as discussed

- in Section 2.3.

The Total Measurement Channel Uncertainty includes the total uncertainty ac- '

commodated between the sensor and the input to the PPS Cabinet., The Total ,

Measurement Channel Uncertainty combined with the PPS Cabinet Uncertainty provides the Total Instrument Channel Uncertainty.

Table 3 contains data for the remainder of the uncertainty components as discussed in Section 2.3.

No Dynamic Allowances are presently applied in the non-CPC portions of the SONGS Setpoint Analysis.

The process uncertainty applied in the High Linear Power Setpoint calculation reflects maximum uncertainties in the ca'lorimetric determination used during calibration.

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4-3

.r ..-

- ,- . , .- - -g a v- --n, -

--w-wr -> rre>-w, =9Q A~'--

. 1408/caf-41 4.2.4 Table 4

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Table 4 contains the Analysis Setpoint data and the margin between the Analysis Setp,oint and the Trip Setpoint. The Analysis Setpoint is the value used in the Safety Analysis at which protection system actuation is assumed to start. The margin between the Analysis Setpoint and the Trip Setpoint is the mathematical difference between the two values. This corresponds to item 5 of the NRC request. In all cases this margin is larger than or equal to the total equipment seror determined in the setpoint calculation. This ensures that a trip actuation will occur prior to the point used in the Safety Analysis.

4.2.5 Table 5 Table 5 contains the Trip Setpoint, Allowable Value and Analysis Setpoint data for the reactor trips generated by the CPCs. As shown, all three values for the low DNBR trip are identical as are all three values for the ,

g High Local Power Density trip. The data in Table 5 corresponds.to items 1 .

and 2 of the NRC request. Because the Trip Setpoint and Allowable Value are identical, the instrument drift allowance for the CPCs - item 3 of the NRC request is zero. The reason for the identical values is explained in Section 2.5.3.4. Basically, the CPC is a digital computer system and is not subject to drift. Because the Trip Setpoint and Analysis Setpoint are identical, the margin between these two values - item 5 of the NRC request is zero. The reasons for these identical values are also explained in Section 2.5.3.4. Basically, the margin is incorporated into the CPC computer algorithms rather than in the Trip Setpoint value itself.

4.2.6 Tables 6 and 7 Tables 6 and 7 contain data on the bias components associated with the measurement signals input to the CPCs. This corresponds to item 4 of the NRC request. Table 7 also gives the total allowance for each input. This is the value used in the determination of the CPC uncertainty constants.

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4-4

. 1.408/caf-42 Table 6 contains measurement channel uncertainties for calibration and j i periodic testing. This is analogous to the same data presented in Table 2.

The A/D conversion allowance represents the calculated uncertainty that must be accounted for at any time between calibrations. This value was used in calculating the total allowance for each instrument input channel.

Table 7 contains the allowances for environmental effects and software roundoff. Also shown is the total allowance for each instrument channel.

The environmental effects data is analogous to the accident environment data prasented in Table 3 for the non-CPC functions. Software round-off ac ounts for the conversion from the data in the binary register after the A/D to the value in the first register where the data is represented in engineering units. This is included in the total process equipment al-lowance calculation. The final column of Table 7 contains the total allowance for ine instrument channel. This total allowance is the value of the measurement uncertainty discussed in Section 2.5.2.1.

4.2.7 _

Additional Notes . .

1. High Logarithmic Power - RPS: The relation between power and millivolts is not linear for this function. All error components are determined and combined in millivolts.
2. High Steam Generator Water Level - RPS: No credit is taken in the Safety Analysis for the operation of this trip function.
3. High Steam Generator Delta Pressure - EFAS: Two separate sensors are used to determine the pressure difference between the steam generators. The uncertainties associated with each sensor are included in the total uncertainty calculation.
4. Low Refueling Water Tank Level - RAS: Two Analysis Setpoints were used in the Safety Analysis. A higher level actuation was analyzed to ensure enough borated water was in the

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, ,1408/ mad-43 containment sump before the RAS was generated. The lower

( level actuation was analyzed to ensure the RAS was generated while the Refueling Water Tank (RWT) still contains enough

, water for proper operation. Where two values are listed, the first applies to the lower Analysis Setpoin'. and the second to the higher Analysis Setpoint. Where one value is listed, it

' applies to both calculations. The Trip Setpoint allows a range for setting, consistent with the calibration uncertainties.

5. CPC RCP Shaft Speed: For both size discs the A/D conversion allowance is not applicable because a binary signal is transmitted to the CPCs.

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4 4-6

.. . ' .1. ~ , _. _ _ . _ . . . . ._ _ . . . . . - . _ ._ . . . _ _

1408/ mad-44

5.0 REFERENCES

I 5.1 Nuclear Regulatory Commission, " San Onofre Nuclear Generating Station Units 2 & 3, Instrument Trip Setpoint Values," letter to Southern California Edison Company, Docket No. 50-361 and 50-362, April 11, 1977.

5.2 Southern California Edison Company, " San Onofre Nuclear Generating Station Units 2 & 3 Technical Specifications."

5.3 Nuclear Regulatory Commission, " Licensing of Production and Utilization Facilities," Rules and Regulations, Title 10, Chapter 1, Code of Federal Regulations - Energy, Part 50.

5.4 Institute of Electrical and Electronics Engineers, " Criteria for Protection Systems for Nuclear Power Generating Stations," IEEE 279-1971 September 20, 1974.

( 5.5 Nuclear Regulatory Commission, " Standard Technical Specifications for Combustion Engineering Pressurized Water Reactors," September 20, 1974. .

5.6 Nuclear Regulatory Commission, " Instrument Setpoints," Regulatory Guide 1.105, Revision 1, November 1976.

5.7 Advisory Committee on Reactor Safeguards,~" Assessment of Light Water Reactor Safety Matters," Transcript of December 3,1976. Page 241 discussion of Item 13 - instrumentation setpoints and related technical specifications.

5.8 C-E Power Systems, Combustion Engineering, Inc., "CPC - Assessment ,

of the Accuracy of P;lR Safety System Actuation as Performed by the Core Protection Calculators," CENPD-170-P, July 1975.

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1408/caf-45 i

5.9 C-E Power Systems, Combustion Engineering, Inc., "CPC - Assessment of I the Accuracy of PWR Sats+.y System Actuation as Performed by the Core Protection Calculators," (.2NDPD-170 Supplement 1-P, November 1975.

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i 5-2

^

1408/ma N 6 - -

I .

I i 2E SE TABLE 1 -

if PPS TRIP SETPOINTS, ALLOWABLE VALUES AND DRITT Fl.LOWANCES e

o PPS FUNCTION TRIP SETPOINT ALLOWABLE VALUE DRIFT ALLOWANCE High Logarithmic 0.89 % 0.96 % 0.07 %

Power Level-RPS High Linear Power 120% FP

  • 121.3 % FP 1.3 T. FP Level-RPS High Pressurizer 2382 psia 2389 psia 7 psia Pressure-RPS -

Low Pressurizer Pressure-RPS/CCAS/ 1806 psia 1763 psia 43 psia ui SIAS/CSAs/CIAS w

High Steam Generator 90 % tap span 90.74 % tap span 0.74 % tap span Water Level-RPS Low Steam Generator 23 % tap span 22.23 % tap span 0.77 % tap span Water Level-RPS/EFAS Low Steam Generator 729 psia 711 psia 18 psia Press-RPS/MSIS/EFAS High Steam Generator 50.0 psid 66.25 psid 16.25 psid Delta Press-EFAS High Containment Press-RPS/CCAS/ 2.95 psig 3.14 psig 0.19 psig SIAS/CIAS/CSAS High High Contain- 8.14 psig 8.83 psig 0.69 psig ment Press-CSAS .

Low Refueling water 18.5 % tap span 17.74%tapshan + 0.76 % tap span Tank Level-RAS 19.26 % tap span 0

1408/mak47 - ,

h TABLE 2 ,

h PPS INSTRUMENT BIAS COMPONENTS

m PPS FUNCTION PPS CABINET PPS MEASUREMENT CHANNEL INITIAL PERIODIC INITI('. PERIODIC TEST High Logarithmic -+ 5.0 mV + 30.30 mV -+ 344.70 mV -+ 346.71 mV Power Level-RPS - 29.20 mV High Linear Power -+ 0.10% FP + 1.26% FP -+ 1.43% FP -+ 1.46% FP Level-RPS - 1. 21 % FP I

High Pressurizer -

+ 1.25 psi + 7.03 psi -+ 7.18 psi + 17.37 psi Pressure-RPS - 7.57 psi .

Low Pressurizer -

+ 3.75 psi + 43.12 psi -+ 11.25 psi -+ 26.25 psi

, Pressure-RPS/CCAS/ - 37.72 psi

i SIAS/CSAS/CIAS 3 High Steam Generator -

+ 0.13 % + 0.77 % -+ 0.89 7, + 1.01 %

Water Level-RPS 6 - 0.71 %

i Low Steam Generator + 0.13 %

+ 0.77 % + 0.89 %

- -+ 1.01 %

Water Level-RPS/EFAS - 0.71 %

Low Steam Generator + 1.50 psi

+ 17.35 psi '+ 8.62 psi

+ 20.84 psi Press-RPS/MSIS/EFAS - 16.25 psi i High Steam Generator + 1.50 psi

+ 11.49 psi + 12.19 psi

+ 29.48

, Delta Press-EFAS - 9.29 psi ,

High Containment '-+ 0.03 psi + 0.18 psi -+ 0.18 psi + 0.42 psi

Press-RPS/CCAS/SIAS - 0.19 psi CIAS/CSAS High High Contain- + 0.12 psi

+ 0.66 psi + 0.65 psi + 1.55 psi ment Press-CSAS - 0.69 psi '

i l Low Re'ueling Water -

+ 0.13 % -+ 0.76 % -

+ 0.80 % -+ 1.24 %

Tank Level-RAS

1408,madA8 .- -

S TABLE 3 .

N PPS INSTRUMENT BIAS COMPONENTS, CONTINUED TOTAL MEASUREMENT CHANNEL PPS FUNCTION UNCERTAINTY DYNAMIC ALLOWANCE PROCESS ERROR High Logarithmic Power i 346.71 mV - -

Level-RPS -

2 High Linear Power + 1.46 % FP

~

- + 4.0% FP

~

Level-RPS I High Pressurizer + 28.87 psi - -

Pressure-RPS ~ 81.87 psi Low Pressurizer Press- + 239.10 psi '

ure-RPS/CCAS/SIAS/CSAS /CIAS - 299.10 psi u.

/.n High Steam Generator + 2.67 % - -

Water Level-RPS - 2.77 %

i Low Stean Generator + 17.27 % - -

i Water Level-RPS/EFAS - 3.40 %

Low Steam Generator + 45.44 psi - -

Press-RPS/MSIS/EFAS - 112.64 psi High Steam Generator -

+ 47.30 psi - -

. Delta Press-EFAS High Containment + 0.65 psi .

1 Press-RPS/CCAS/ - 1.01 psi SIAS/CIAS High High Contain- + 2.44 psi - -

ment Press-CSAS - 3.75 psi Low Refueling Water + 2.81 % '

, Tank Level-RAS - 3.58 %

1408/ma N 9 /

h TABLE 4 ,

Yo PPS ANALYSIS SETPOINTS AND SETPOINT MARGINS e

to PPS FUNCTION ANALYSIS SETPOINT MARGIN BETWEEN ANALYSIS SETPOINT s

& TRIP SETPOINT High Logarithmic Power 2 % of rated full power 1.11 %

Level-RPS High Linear Power 125 % 5%

Level-RPS High Pressurizer 2422 psia '.40 psia Pressure-RPS Low Pressurizer 1560 psia '

246 psi Pressure-RPS/CCAS/SIAS/CSAS/

u, CTAS 4, High Steam Generator 93% tap span 3%

4 W6ter Level-RPS j

Low Steam Generator . 5% tap span 18%

Water Level RPS/EFAS ,

Low Steam Generator 678 psia 51 psia Press-RPS/MSIS/EFAS High Steam Generator 100 psid 50.0 psi Delta Press-EFAS i

1.05 psi High Containment Press- 4.0 psig .

RPS/CCAS/SIAS/CIAS/CSAS 4

High High Containment 12.0 psig 3.86 psi Press-CSAS . .

Low Refueling Water 18.5% (1) '

(1)

Tank Level-RAS ,

(1) The 18.5% level allows sufficient margin to account for all uncertainties in both the positive and negative direction.

1408/nNd-jiQ _- . _ .

E j -

TABLE 5 es

g PPS CORE PROTECTION CALCULATOR TRIP SETPOINT DATA
M i

PPS FUNCTION TRIP SETPOINT ALLOWABLE VALUE ANALYSIS SETPOINT ,

1 i Low DNBR-RPS 1.19 1.19 1.19 High Local Sower 21 kw/ft 21 kw/ft 21 kw/ft j Density-RPS d

W 4

i

l. .

i - ,

i l

f I .

i .

L 4

. 1408/ mad-ji.) - , -

.j .

a .

TABLE 6 ~

h PPS CORE PROTECTION CALCULATOR PROCESS EOUIPMENT BIAS COMPONENTS 3

MEASUREMENT CHANNEL CPC INPUT FUNCTION INITIAL PERIODIC TEST A/D CONVERSION ,

Pressurizer Pressure 1 7.19 psi i 17.37 psi + 3.31 psi

- 3.38 psi Hot Leg Temperature + 1.08'F + 1.24*F +0.49 F

-0.51*F j Cold Leg Temperature i 1.08'F + 1.24*F , +0.49oF

' -0.51*F CEA Position + 2.89 in + 2.89 in + 0.35 in u, - 3.09 in - 3.09 in - 0.47 in 5e Ex-Core Linear + 1.03 FP

~~ '-+ 1.08% FP + 0.263% FP Subchannels - 0.267% FP RCP Shaft Speed- + 1.456 RPM + 1.456 RPM

+ 0.294 RPM 28 Inch Disc

- 0.247 RPM

~

RCP Shaft Speed- + 3.329 RPM -+ 3.329 RPM + 0.294 RPM i

16.969 Inch Disc

- 0.247 RPM 3

1 j ..

A m a n TABLE 7 ,

~ .

n PPS CORE PROTECTION CALCULATOR PROCESS EQUIPMENT BIAS COMPONENTS, CONTINUED, AND TOTAL ALLOWANCES' I CPC INPUT FUNCTION ENVIRONMENTAL EFFECTS' SOFTWARE ROUND-OFF TOTAL ALLO 11ANCES Pressurizer Pressure + 21.00 psi - + 27.80 psi

- 91.70 psi - 98.47 psi Hot Leg Temperature + 0.44 "F -

+ 1.40 *F

- 1.41 "F Cold Leg Temperature + 0.42 'F -

+ 1.39 *F i . 1.41 'F i

CEA Position + 2.00 in -

+ 5.03 in

!? - 0.90 in -

4.08 in 1* N.A; Ex-Core Linear - - + '.11

% FP
Subchannels -

1.12 % FP -

RCP Shaft Speed- N.A. .

- + 1.997 RPM j 28 Inch Disc _

1.503 RPM -

RCP Shaft Speed- N.A. -

+ 3.G70 RPM 16.969 Inch Disc _, 3.376 RPM li '

I l .

j -

i 4

l .

(

TRIP POINT VALUE USED IN INSTRUT.1ENTATION ENVIRONT.1E N TAL PROCESS Tile SAFETY ANALYSIS ERRORS ERRORS ERRORS I

ANALYSIS SETPOINT U

^

ANALYSISSETPOINT ALTERED BY THE TOTAL ERROR VALUE IN A CONSERVATIVE DIRECTION <

EQUIPl.1ENT SETPOINT U BISTAB LE EQUIPMENT SETPOINT ALTERED DRIFT.

BY Tile BISTABLE DRIFT VALUE . .

( TOWARD THE ANALYSISSETP31NT<-

ALLOWABLE VALUE

(

Figure SETPOINT CALCULATION METHODOLOGY j

n - -

ANALYSIS SETPOINT ,

ESTIMATED EQUIPMENT ERRORS

$ . NOMINAL VALUE -

a p

l E -

!G ESTIMATED

" EQUIPMENT ERRORS 4

o "

E MOST LIMITING VALUE = .

_" OF OPERATING RANGE E

2 r-o m i g

I  ! b  !

g .

I I PERFORMANCE RELATED DBE VALUES q d pSTEADY STATE VALUE i  :

o Z

e g

E O

{ .

CURRENT LOOP -p 1,dTABLE SENSOR > T R ANSMITTER + CONVERTER >

RESISTOR COMPARATOR I

l 1 r POWER COINCIDENCE SUPPLY LOGlc l

INITIATION

' RELAY

+ ACTUATION

( ,

I

< PROCESS EQUIPMENT = 4 PPS >

L CABINET *!* RPS:RTSG ,

ESF: AUXILIARY RELAY CABINET l

l 1

l

(

(

1 Figure PLANT PROTECTION SYSTEM OLOCK DI AGRAM f 3 I -

,y_ , , . . - - , . . . - - . . . . , - - - -- - - - - - ---,-,,,m -- -- - - - - - ,-

(

4 ALL ANALYZED EVENTS >

EVENT SPECIFIC ANALYSES:

g ANALYSIS SETPOINT g ANALYSIS SETPOINT TOTAL ANALYSIS SETPOINT EQUIPMENT li ERROR TOTAL TOTAL -

( EQUIPMENT ERROR EQUIPMENT ERROR V

p p EQUIPMENT SETPOINT i

l

(

Figure EQUIPMENT SETPOINT DETERMINATION USING EVENT SPECIFIC DATA 4

---v-- w w 9ww _m-,--,.,+g-a _w ---- - - .,.p __

w- _- ..y, ,.- .. _,,c--%.~.g--, ,7 -w -w -

( , .

NUCLEAR FLUX POWER --6 BISTABLE COMPARATOR > HIGH LINEAR POWER

> BISTABLE COMPARATOR

> lilGH LOGARITHMIC POWER CEA POSITIONS COLD LEG TEMPER ATURE- > DIGITAL HOT LEG TEMPERATURE - > CALCULATOR > LOW DNBR REACTOR COOLANT PUM SPEED

> BISTABLE COMPARATOR > HIGH PRESSURIZER PRESSURE PRESSURIZER PRESSURE > BISTABLE COMPARATOR > LOW PRESSURIZER P,RESSURE ,

I STEAM GENERATOR > BISTABLE COMPARATOR LOW STEAM GENERATOR PRESSURE > PRESSURE STEAM GENERATOR > BISTABLE COMPARATOR > LOW STEAM GENERATOR LEVEL LEVEL

> BISTABLE COMPARATOR > HIGH STEAM GENERATOR LEVEL CONTAINMENT PRESSURE > " ^'" "

BISTABLE COMPARATOR > PR SURE TURBINE TRIP SIGNAL > BISTABLE --->. LOSS OF LOAD TRIP

(

g figure REACTOR PROTECTION SYSTEM INPUTS AND TRIP FUNCTIONS 5

1 l

\

l i

-t> BISTABLE DIGITAL COMPUTER

-q 1r PROCESS EQUIPMENT -C> A/D 1 OGIC g( INPUT I I I I

CPC MEASUREMENT UNCERTAINTY 3r L_ --- COMPONEMTS----------J INITIATION + AC M ION net.3y PROCESS CORE pp3

< > :: PROTECTION >4 * "

EQUIPMENT CASINET CALCULATOR I

l CORE PROTECTION CALCULATOR AS PART OF THE REACTOR 0

PRO (ECTION SYSTEM

_ _ _ _ - . _ . . . _ _ _ . _ . _ . . , _ _ ._.. . ._._ _ _ _ . _ . --_ . _ - - _ - - - . .__ _--

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