DCL-13-016, Attachment 5 to DCL-13-016 - WCAP-17706-NP, Revision 0, Westinghouse Setpoint Methodology as Applied to the Diablo Canyon Power Plant.
Text
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Westinghouse Non-Proprietary Class 3 WCAP-17706-NP January 2013 Revision 0 Westinghouse Setpoint Methodology as Applied to the Diablo Canyon Power Plant Westinghouse
WESTINGHOUSE NON-PROPRIETARY CLASS 3 WCAP-17706-NP Revision 0 Westinghouse Setpoint Methodology as Applied to the Diablo Canyon Power Plant Charles R. Tuley*
Setpoints and Uncertainty Analysis January 2013 Reviewer: Terrence P. Williams*
Setpoints and Uncertainty Analysis Approved: Ryan P. Rossman, Manager*
Setpoints and Uncertainty Analysis
- Electronically approvedrecords are authenticatedin the electronic document management system Westinghouse Electric Company LLC 1000 Westinghouse Drive Cranberry Township, PA 16066
© 2013 Westinghouse Electric Company LLC All Rights Reserved
TABLE OF CONTENTS LIST OF TA B L E S .............................................................................................................................................. iii L IST O F FIG U RE S ............................................................................................................................................ iv 1.0 INTR O D UCT ION .................................................................................................................................. 1 2.0 COMBINATION OF UNCERTAINTY COMPONENTS ............................................................. 3 2 .1 M ethodo logy ............................................................................................................................. 3 2.2 Sensor A llow ances ............................................................................................................. 5 2.3 R ack A llow ances .............................................................................................................. 8 2.4 Process A llow ances ........................................................................................................... 10 2.5 Dig ital Functions ..................................................................................................................... 10 3.0 PROTECTION SYSTEM SETPOINT METHODOLOGY .............................................................. 11 3.1 Setpoint C alculations .............................................................................................................. 11 3.2 Setpoint Methodology Definitions ..................................................................................... 12 4.0 WESTINGHOUSE CALIBRATION AND DRIFT EVALUATION PROCESS ....................... 26 a,c 5.0 APPLICATION OF THE WESTINGHOUSE SETPOINT METHODOLOGY ............. 34 5.1 Uncertainty Calculation Basic Assumptions / Premises .................................................. 34 5.2 Process Rack Operability Assessment Program and Criteria ........................................... 36 5.3 Application of Process Rack Operability Assessment to the Plant Technical S pecifi cations .......................................................................................................................... 37 5.4 Sensor/Transmitter Operability Assessment Program and Criteria ................................ 38 5.5 Application of the Sensor/Transmitter Operability Assessment ..................................... 39 WCAP- 17706-NP January 2013 i Revision 0
6.0 SU M MA RY O F IM PO RTA N T PO INTS ...................................................................................... 41 7.0 REFEREN C ES ..................................................................................................................................... 46 January 2013 I 7706-NP WCAP- 17706-NP January 2013 Revision 0 ii
LIST OF TABLES Table 3-1 AP Measurements Expressed in Flow Units ................................................................................ 24 WCAP- 17706-NP January 2013 iii Revision 0
LIST OF FIGURES Figure 3-1 Westinghouse Setpoint Parameter Relationship Diagram (Increasing Function) ................. 23 Figure 4-1 Westinghouse Calibration and Drift Data Evaluation Process Diagram ............................... 33 WCAP- I 7706-NP January 2013 iv Revision 0
1.0 INTRODUCTION
This document identifies the three basic instrument uncertainty algorithms for the; 1) reactor trip system (RTS) trip functions, engineered safety features actuation system (ESFAS) protection functions, 2) control system functions assumed as initial condition assumptions in the Westinghouse Improved Thermal Design Procedure (ITDP) (Reference 1) and safety analyses, and 3) control board and computer indication of plant parameters utilized by the control room operators to confirm proper operation of the control and protection instrumentation for the Pacific Gas and Electric Company (PG&E) Diablo Canyon Power Plant (DCPP). These algorithms, when supported by appropriate plant procedures and equipment qualification, are believed to provide total instrument loop uncertainties, termed Channel Statistical Allowance (CSA), at a two-sided 95 % probability and 95 % confidence level; as stated in U.S. Nuclear Regulatory Commission Regulatory Guide (RG) 1.105, Revision 3, Regulatory Position, C. I (Reference 2). [
pac This document is divided into four principal sections. Section 2.0 identifies the current, Westinghouse generalized algorithm (Eq. 2.1) used as the basis to determine the overall instrument uncertainty for an RTS or ESFAS function. This specific algorithm evolved from a Westinghouse paper presented at an Instrument Society of America/Electric Power Research Institute (ISA/EPRI) conference in June 1992 (Reference 3). This approach is consistent with the American National Standards Institute (ANSI)/ISA standard, ANSI/ISA-67.04.01-2006 (Reference 4). The basic uncertainty algorithm is the square root sum of the squares (SRSS) of the applicable uncertainty terms, which is endorsed by the standard. All appropriate and applicable uncertainties, as defined by a review of the plant baseline design input documentation, have been included in each RTS or ESFAS function uncertainty calculation.
ISA-RP67.04.02-2010 (Reference 5) was considered, as a general guideline, but each uncertainty and its treatment is based on Westinghouse methods which are consistent or conservative with respect to this document. The current version of NRC RG 1.105, Revision 3, endorses the 1994 version of ISA S67.04, Part I. Westinghouse has evaluated this NRC document and has determined that the uncertainty algorithms contained in Section 2.1 and the setpoint calculations contained in the DCPP specific companion document, WCAP-17696-P (Reference 6) are consistent with the guidance contained in RG 1.105 Revision 3 and NRC Branch Technical Position (BTP) 7-12 Revision 5 (Reference 7). It is believed that the total channel uncertainty, CSA, represents a two-sided 95/95 value as requested in RG 1.105 Revision 3. Two variations of the protection function uncertainty algorithm are presented to demonstrate the Westinghouse treatment of uncertainties for control functions and parameter indication.
Section 3.0 of this report lists definitions of terms and associated acronyms used in the RTS or ESFAS function, control and indication uncertainty calculations. Appropriate references to industry standards have been provided where applicable. Included in this section are detailed descriptions of the uncertainty terms for a typical RTS or ESFAS, control and indication function uncertainty calculations performed by WCAP- 17706-NP January 2013 I Revision 0
Westinghouse. Function specific setpoint calculations specific to DCPP are contained in the companion document WCAP- 17696-P (Reference 6).
Section 4.0 contains an overview of the Westinghouse evaluation process for calibration and drift data. It describes the basic approach utilized [
]a,, This process has been in use for over 15 years in the evaluation of surveillance data. It was last used specific to DCPP to generate the transmitter drift magnitudes identified in WCAP-1 1082 Revision 6 (Reference 8) and WCAP- 11594 Revision 2 (Reference 1). This process was last described to the NRC. in a Westinghouse presentation in March 2007 (Reference 10).
Section 5.0 provides a description of the Westinghouse recommendations for implementation of the Westinghouse Setpoint Methodology (WSM) in the DCPP Technical Specifications and the assessment of operability of sensor/transmitters and process racks.
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2.0 COMBINATION OF UNCERTAINTY COMPONENTS This section describes the Westinghouse Setpoint Methodology for the combination of the uncertainty components utilized for protection, control and indication functions. The methodology used in the determination of the overall CSA is noted in Section 2.1. All appropriate and applicable uncertainties, as defined by a review of DCPP baseline design input documentation, are included in each protection, control or indication function CSA calculation.
2.1 Methodology The methodology used to combine the uncertainty components for a channel is an appropriate combination of those groups that are statistically and functionally independent. Those uncertainties considered dependent are conservatively treated by arithmetic summation and then systematically combined with the independent terms.
As noted previously, the basic methodology used is an SRSS. This basic approach, or others of a similar nature, has been used for Westinghouse uncertainty and setpoint calculations for over 30 years:
protection function instrument uncertainty calculations - June 1978 (Reference 11), statistical Departure from Nucleate Boiling calculations - WCAP-8567-P-A (Reference 12) and AP1000l) plant protection function uncertainties - WCAP-1636 I-P (Reference 13). WCAP-8567 was approved by the NRC, noting acceptability of statistical techniques for the application requested, in April 1978 (Reference 12). WCAP-16361-P was approved by the NRC in August 2007 (Reference 14). Several standards, ISA 67.04.01 (Reference 4) and American Nuclear Society (ANS) Standard 58.4 (Reference 15) approve the use of probabilistic and statistical techniques in determining safety-related setpoints.
The generalized relationship between the uncertainty components and the calculated uncertainty for an RTS or ESFAS protection channel is noted in Eq. 2.1:
[IPMA2 + PEA 2 + SRA2 + (SMTE+ SD) 2 + (SMTE + SCA) 2 +1 CSAPR°T = SPE 2 +STE 2 + (RMTE+ RD) 2 + (RMTE+ RCA) 2 +RTE 2 Eq. 2.1 API000 is a trademark or registered trademark of Westinghouse Electric Company LLC, its affiliates and/or subsidiaries in the United States of America and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners.
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The generalized relationship between the uncertainty components and the calculated uncertainty for a control channel is noted in Eq. 2.2 (subscript IND denotes indication - control board meter or plant process computer):
axc Eq. 2.2 The generalized relationship between the uncertainty components and the calculated uncertainty for an indication channel is noted in Eq. 2.3 (subscript IND denotes indication - control board meter or plant process computer):
a7c Eq. 2.3 Where:
CSA Channel Statistical Allowance PMA = Process Measurement Accuracy PEA Primary Element Accuracy SRA = Sensor Reference Accuracy SMTE = Sensor Measurement and Test Equipment Accuracy SD = Sensor Drift SCA = Sensor Calibration Accuracy SPE = Sensor Pressure Effects STE = Sensor Temperature Effects RMTE = Rack Measurement and Test Equipment Accuracy RD = Rack Drift RCA = Rack Calibration Accuracy RTE Rack Temperature Effects EA = Environmental Allowance WCAP- 17706-NP January 2013 4 Revision 0
BIAS One directional, known magnitude allowance CA Controller Accuracy READOUT = Readout Device Accuracy
]ac I
Each of the previous terms is defined in Section 3.2, Setpoint Methodology Definitions.
The equations are based on the following:
- 1. Sensor and rack measurement and test equipment uncertainties are treated as dependent parameters with their respective drift and calibration accuracy terms.
- 2. [
]a.C The term is arithmetically summed with the SRSS in the direction of conservatism.
- 3. Bias terms are one directional with known magnitudes (which may result from several sources, e.g., drift or calibration data evaluations) and are also arithmetically summed with the SRSS.
- 4. a,c Consistent with RG 1.105 Rev. 3, Regulatory Position C.1 (Reference 2), the CSA value from Eq. 2.1 is believed to be determined at a 95 % probability and at a 95 % confidence level (95/95) on a two-sided basis. The control function CSA value from Eq. 2.2 and the indication function CSA value from Eq. 2.3 are believed to be determined at a 95 % probability and at a 95 % confidence level (95/95) on a two-sided basis, consistent with the requirements of the ITDP (References I and 12). Eq. 2.1, Eq. 2.2 and Eq. 2.3 were used as the basis for the DCPP setpoint calculations documented in WCAP- 17696-P (Reference 6).
2.2 Sensor Allowances Seven parameters are considered to be sensor allowances: SRA, SCA, SMTE, SD, STE, SPE and EA.
Three of these parameters are considered to be independent, two-sided (-), unverified (by DCPP calibration or drift determination processes), vendor supplied terms (SRA, STE and SPE). Based on vendor supplied data, typically product data sheets and qualification reports, these parameters are treated as two-sided 95/95 values unless specified otherwise by the vendor. Three of the remaining parameters WCAP- 17706-NP January 2013 5 Revision 0
are considered dependent with at least one other term, are two-sided (+), and are the result of the DCPP calibration and drift determination process (SCA, SMTE and SD). Through appropriate treatment of DCPP data, these parameters are treated as two-sided 95/95 values. EA, as described later in this section, is conservatively treated as a limit of error.
SRA is the manufacturer's reference accuracy that is achievable by the device. This term is introduced to address repeatability and hysteresis effects when performing only a single pass calibration, i.e., one up and one down. If a verification of all three aspects of the sensor reference accuracy, hysteresis, repeatability and linearity, as defined by ISA-5 1.1 (Reference 16, p. 61), is performed as part of the calibration process, the value of SRA can be set to zero. STE and SPE are considered to be independent due to the manner in which the instrumentation is checked; i.e., the instrumentation is calibrated and drift is determined under conditions in which pressure and temperature are assumed constant. For example, assume a sensor is placed in some position in the containment during a refueling outage. After placement, an instrument technician calibrates the sensor at ambient pressure and temperature conditions.
Sometime later with the plant shutdown, an instrument technician checks for sensor drift using the same technique as was previously used for calibrating the sensor. The conditions under which this drift determination is made are again ambient pressure and temperature. The temperature and pressure should be essentially the same at both measurements. Thus, they should have no significant effect on the drift determination and are, therefore, independent of the drift term.'
SCA and SD are considered to be dependent with SMTE due to the manner in which the instrumentation is evaluated. A transmitter is calibrated by providing a known process input (measured with a high accuracy gauge) and evaluating the electrical output with a digital multimeter (DMM) or digital voltmeter (DVM). The gauge and DVM accuracies form the SMTE terms. The transmitter response is known, at best, to within the accuracy of the measured input and measured output. Thus, the calibration accuracy (SCA) is functionally dependent with the measurement and test equipment (SMTE). Since the gauge and DVM are independent of each other (they operate on two different physical principles), the two SMTE terms may be combined by SRSS prior to addition with the SCA term. Transmitter drift is determined using the same process used to perform a transmitter calibration. That is, a known process input (measured with a high accuracy gauge) is provided and the subsequent electrical output is measured with a DMM or DVM. Thus, the drift value (SD) is functionally dependent with the measurement and test equipment (SMTE) and is treated in the same manner as SMTE and SCA.
While the data is gathered in the same manner, SD is independent of SCA in that they are two different parameters. SCA is the difference between the As Left value and the Desired value. SD is the difference between the As Found value of the current calibration and the As Left value of the previous calibration. It is assumed that a
]a,c WCAP-17706-NP January 2013 6 Revision 0
Transmitters are designed and subsequently verified through qualification [
]ac to be able to withstand adverse elevated temperatures from exposure to design basis events (DBE) due to mass and energy loss from a break in the primary or secondary side piping. This is addressed in the uncertainty calculation by the inclusion of an EA temperature term. Vendor specifications typically identify the transmitter response as a "+/-"term, indicating that the transmitter may respond in either the indicated higher than actual direction or indicated lower than actual direction when exposed to significantly elevated temperatures. Because of this identification, this term may be interpreted by many to be a random variable.
]a'C This suggests that on a plant specific basis, the more appropriate treatment of the EA temperature uncertainty term is as a limit of error, i.e., as a bias, and not as a random term.
ax Transmitters are designed and subsequently verified through qualification testing, to be able to withstand exposure to high doses of radiation due to mass loss from a break in the primary side piping. This is addressed in the uncertainty calculation by the inclusion of an EA radiation term. Vendor specifications typically identify the device response as a "+" term, indicating that the transmitter may respond in either WCAP- 17706-NP January 2013 7 Revision 0
the indicated higher than actual direction or indicated lower than actual direction when exposed to significant radiation. Because of this identification, this term may be interpreted by many to be a random variable. [
]a.c This suggests that on a plant specific basis, the more appropriate treatment of the EA radiation uncertainty term for a pressurizer pressure transmitter is as a limit of error, i.e., as a bias, and not as a random term.
a,c 2.3 Rack Allowances Rack Reference Accuracy (RRA) is the manufacturer's reference accuracy that is achievable by the process rack instrument string. This term is introduced to address repeatability and hysteresis effects not addressed by the performance of a single pass calibration, i.e., one up and one down. For DCPP, the Invensys process racks have a self calibration feature where it is noted that the RCA term includes the effects of the RRA, RTE and RD terms. Based on information provided by Invensys, [
]a'c Thus, for the Invensys process racks, the RRA, RTE and RD terms are set to a magnitude of 0 % span in the treatment of process rack uncertainties. For the CS Innovations (CSI) Advanced Logic System (ALS) cards, the [
]"C Based on information provided by CSI, this parameter is treated as
]a.C for the ALS cards. Thus, for the ALS process rack cards, the
]a'c in the treatment of process rack uncertainties.
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Four parameters are considered to be rack allowances. Two parameters are applicable to both Invensys and CSI cards; RCA and RMTE. Two parameters are applicable to only the CSI cards; RTE and RD. The first to be discussed, RTE, is considered to be an independent, two-sided (+/-), unverified (by plant calibration or drift determination processes), vendor supplied parameter. The process racks are located in an area with ambient temperature control, making consistency with the rack evaluation temperature easy to achieve. Based on information provided by CSI, this parameter is treated as
]a~c for the ALS cards.
RCA and RD are considered to be two-sided (+) terms dependent with RMTE. The functional dependence is due to the manner in which the process racks are evaluated. In order to calibrate or determine drift for the process rack portion of a channel, a known input (in the form of a voltage, current or resistance) is provided and the point at which the trip unit changes state is measured. The input parameter is either measured by the use of a DMM or DVM (for a current or voltage signal) or is known to some degree of precision by use of precision equipment, e.g., a precision decade box for a resistance input. For simple channels, only a DMM or DVM is necessary to measure the input and the state change is noted by a light or similar device. For more complicated channels, multiple DVMs may be used or a DVM in conjunction with a decade box. The process rack response is knownat best to within the accuracy of the measured input and indicated output. Thus the calibration accuracy (RCA) is functionally dependent with the measurement and test equipment (RMTE). In those instances where multiple pieces of measurement and test equipment are utilized, the uncertainties are combined via SRSS when appropriate.
The RCA term represents the total calibration uncertainty for the channels, which are calibrated as a single string. Drift for the process racks is determined using the same process used to perform the rack calibration, and in most cases utilizes the same measurement and test equipment. Thus, the drift value (RD) is also functionally dependent with the measurement and test equipment (RMTE) and is treated in the same manner as RMTE and RCA.
While the data is gathered in the same manner, RD is independent of RCA in that they are different parameters. RCA is the difference between the As Left value and the Desired value. RD is the difference between the As Found of the current calibration and the As Left values of the previous calibration. The RD term represents the drift for all process rack modules in an instrument string, regardless of the channel complexity. For multiple instrument strings there may be multiple RD terms, e.g., Overtemperature AT.
It is assumed that a
]a c For DCPP and the Invensys process racks, RD is included as part of the RCA term due to the self calibration process, as noted previously. Based on the appropriate treatment of DCPP data, the RCA and RD parameters are treated as two-sided 95/95 values.
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Process racks are not designed to withstand exposure to high environmental temperatures or radiation.
Therefore, no EA allowances for temperature or radiation are included in the algorithm. No post-seismic event residual error has been noted for either the Invensys or the CSI ALS cards, thus, no seismic term has been included in the uncertainty calculations for the process racks.
2.4 Process Allowances The PMA and PEA parameters are considered to be independent of both sensor and rack parameters. The PMA terms provide allowances for the non-instrument related effects; e.g., neutron flux distribution, calorimetric power uncertainty assumptions, temperature streaming in a pipe, process pressure effects or fluid density changes. There may be more than one independent PMA uncertainty allowance for a channel, if warranted. The PEA term typically accounts for uncertainties due to metering devices, such as elbows, venturis, and orifice plates. In this application, PEA is limited by Westinghouse to RCS Flow (Cold Leg Elbow Taps) and Feedwater Flow for the DCPP RTS/ESFAS uncertainty calculations. PEA may also be used for the uncertainties associated with potential transformers for Undervoltage and Underfrequency functions. In these applications, the PEA term has been determined to be independent of the sensors and process racks. It should be noted that treatment as an independent parameter does not preclude determination that a PMA or PEA term should be treated as a bias. If that is determined to be appropriate, Eq. 2.1 would be modified such that the affected term would be treated by arithmetic summation with appropriate determination and application of the sign of the uncertainty.
2.5 Digital Functions The treatment of digital functions varies to some extent due to the type of function. For example, indication via the plant process computer is quite simplistic in nature; add an Analog to Digital (AID) converter to the rack allowances.
]a.c For the CSI ALS cards,
]".' For digital protection functions, the Nominal Trip Setpoint (NTS) is defined as a single value in voltage, current, resistance or an engineering unit (psia, psig, % span, % Rated Thermal Power, % level)
]ac WCAP-17706-NP January 2013 10 Revision 0
3.0 PROTECTION SYSTEM SETPOINT METHODOLOGY This section contains definitions of terms used in the instrument uncertainty calculations.
3.1 Setpoint Calculations The setpoint calculations for each RTS, ESFAS and control function affected by the digital replacement process protection system are listed in Tables 3-1 through 3-19 of WCAP-17696-P (Reference 6). Each table includes a listing of the applicable terms for the function uncertainty and setpoint calculations:
- Model of sensor/transmitter
- Type of process rack
- Listing of each uncertainty parameter, noting -
- Value (% span) or applicability
" Notes applicable to the parameter
- Algorithm utilized
- Algorithm with parameter values (% span) filled in
- Safety Analysis Limit (engineering units)
- Nominal Trip Setpoint (engineering units)
- Instrument span
- Total Allowance (TA) (% span)
- CSA (% span)
- Margin (% span)
- Transmitter operability criteria
- As Left Tolerances (% span)
- As Found Tolerances (% span)
- Process rack operability criteria
- As Left Tolerances (% span)
- As Found Tolerances (% span)
Westinghouse reports TA, CSA and Margin values to one decimal place using the technique of:
- Rounding down values < 0.05 % span,
- Rounding up values > 0.05 % span.
This rounding process is based on the limiting accuracy of the least known parameter, typically calibration or drift, of an analog process channel or process measurement accuracy for a digital process channel.
Parameters reported as:
- "N/A" are not applicable, i.e., have no value, for that channel, WCAP- 17706-NP January 2013 11 Revision 0
- "0" are applicable but are included in other terms, e.g., normalized parameters, "0.0" 4 are applicable with a value less than 0.04 % span.
Table 3-1 provides the derivation of the translation of differential pressure span to % nominal flow and
% flow span for flow functions.
3.2 Setpoint Methodology Definitions For the channel uncertainty algorithms noted in this report, the following definitions are provided, in alphabetical order:
- Analog to Digital Convertor (A/D)
An electronic circuit module that converts a continuously variable analog signal to a discrete digital signal via a prescriptive algorithm.
- As Found The condition in which a transmitter, process rack module, or process instrument loop is found after a period of operation.
- As Found Tolerance (AFT)
The As Found limit identified in the plant surveillance procedures. This defines a significant operability criterion for the instrument process rack and the transmitter. It is a sufficient condition to satisfy an operability assessment for an instrument process rack. The AFT for the instrument process rack is the same as (equals) the As Left Tolerance (ALT) or instrument process rack calibration accuracy, i.e., AFT = ALT = RCA, see Figure 3-1. For process racks, the AFT is a two-sided parameter (+/-) about the NTS. The AFT for transmitters is defined as the sensor drift magnitude identified in the uncertainty calculations. For transmitters, the AFT is a two-sided parameter (-) about the calibration points, e.g., 0 %, 25 %, 50 %, 75 % and 100 % span (an absolute drift parameter), or the AFT is a two-sided parameter (+/-) about the calibration recorded As Left points (a relative drift parameter).
___ a,C WCAP- I 7706-NP January 2013 12 Revision 0
ac
- As Left The condition in which a transmitter, instrument process rack module, or process instrument loop is left after calibration or trip setpoint verification. This condition is typically better than the calibration accuracy for that piece of equipment.
- As Left Tolerance (ALT)
The As Left limit identified in the plant calibration procedures. This defines the initial operability criterion for the instrument process rack (see Figure 3-1) or the transmitter. It is a necessary condition to satisfy an operability assessment for an instrument process rack or transmitter. The ALT is defined as the appropriate calibration accuracy in the uncertainty calculations for the sensor or associated instrument process rack string. For process racks, the ALT is a two-sided parameter (+/-) equal to the RCA about the NTS, see Figure 3-1. The ALT for transmitters is defined as the two-sided (+/-) sensor calibration accuracy magnitude indentified in the uncertainty calculations about the desired calibration points, e.g., 0 %, 25 %, 50 %, 75 % and 100 % span.
a,c
- Bias
- A parameter with a known consistent arithmetic sign, e.g., heatup effect on a level channel Reference Leg.
" A parameter that is treated as a limit of error, e.g., transmitter heatup in a Steambreak elevated temperature environment.
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0 Channel The sensing and process equipment, i.e., transmitter to bistable (analog process racks) or transmitter to trip output (digital process racks), for one input to the voting logic of a protection function. Westinghouse designs protection functions with voting logic made up of multiple channels, e.g. 2 out of 3 Steam Generator Level - Low-Low channels for one steam generator must have their bistables in the tripped condition for a Reactor Trip to be initiated. For control functions, a channel is the sensing and process equipment through the controller module. For indication functions, a channel is the sensing and process equipment through the indicator (control board or Plant Process Computer).
Channel Statistical Allowance (CSA)
The combination of the various channel uncertainties via SRSS, other statistical, or algebraic techniques. It includes instrument (both sensor and process rack) uncertainties and non-instrument related effects, e.g., Process Measurement Accuracy, see Eq.(s) 2.1, 2.2 and 2.3. This parameter is compared with the Total Allowance for determination of instrument channel margin, see Figure 3-1. For a protection function the uncertainties included in, and the conservatism of, the CSA algorithm results in a CSA magnitude that is believed to be determined on a two-sided 95 % probability / 95 % confidence level (95/95) basis.
Controller Accuracy (CA)
Allowance for the accuracy of the controller rack module(s) that performs the comparison and calculates the difference between the controlled parameter and the reference signal at the steady state null point.
" Digital to Analog Convertor (D/A)
An electronic circuit module that converts a discrete digital signal to a continuously variable analog signal via a prescriptive algorithm.
" Environmental Allowance (EA)
The change in a process signal (transmitter or process rack output) due to adverse environmental conditions from a limiting design basis accident condition or seismic event. Typically this value is determined from a conservative set of enveloping conditions and may represent the following:
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" Temperature effects on a transmitter
- Radiation effects on a transmitter
- Seismic effects on a transmitter
" Temperature effects on a level transmitter reference leg
" Temperature effects on signal cable, splice, terminal block or connector insulation
" Seismic effects on process racks Margin The calculated difference (in % instrument span) between Total Allowance (TA) and Channel Statistical Allowance (CSA).
Margin = TA - CSA Margin is defined to be a non-negative number i.e., Margin Ž0 % span, see Figure 3-1.
]a~c
- Nominal Trip Setpoint (NTS)
The trip setpoint defined in the uncertainty calculation and reflected in the plant procedures. This value is the nominal value programmed into the digital instrument process racks or the nominal value to which the bistable is set (as accurately as reasonably achievable) for analog instrument process racks. The NTS is based on engineering judgement (to arrive at a Margin > 0 % span), or.
a historical value, that has been demonstrated over time-to result in adequate operational margin, see Figure 3-1. Based on the requirements of 10 CFR 50.36(c)(1)(ii)(A), Westinghouse defines the NTS as the Limiting Safety System Setting (LSSS) for the RTS and ESFAS functions listed in the DCPP Technical Specifications, i.e., Tables 3.3.1-1 and 3.3.2-1.
" Normalization The process of establishing a relationship, or link, between a process parameter and an instrument channel. This is in contrast with a calibration process. A calibration process is performed with independent known values, i.e., a bistable is calibrated to change state when a specific voltage is reached. This voltage corresponds to a process parameter magnitude with the relationship established through the scaling process. A normalization process typically involves an indirect WCAP- 17706-NP January 2013 15 Revision 0
measurement, [
]a,c Primary Element Accuracy (PEA)
Uncertainty due to the use of a metering device. In Westinghouse RTS/ESFAS calculations, this parameter is used for a venturi, orifice or elbow. This is a calculated or measured accuracy for the device. PEA may also be used for the uncertainties associated with potential transformers for Undervoltage and Underfrequency functions.
- Process Loop or Instrument Process Loop The process equipment for a single channel of a protection, control or indication function.
- Process Measurement Accuracy (PMA)
An allowance for non-instrument related effects which have a direct bearing on the accuracy of an instrument channel's reading, e.g., neutron flux distribution, calorimetric power uncertainty assumptions, temperature streaming (stratification) in a large diameter pipe, process pressure effects or fluid density changes in a pipe or vessel.
- Process Racks The modules downstream of the transmitter or sensing device, which condition a signal and act upon it prior to input to a voting logic system. For analog process systems, this includes all the equipment contained in the process equipment cabinets, e.g., conversion (dropping) resistor, loop power supply, rate function, function generator, summator, control/protection isolator, and bistable (protection function), controller module (control function), meter (control board indication) or Analog to Digital (A/D) conversion module (process computer). For digital process systems, this again includes all the equipment contained in the process equipment cabinets, e.g., conversion (dropping) resistor, A/D signal conditioning module, processor module and trip module (protection function), D/A output module and controller module (analog control function), D/A output module and meter (analog control board indication) and D/A output module and A/D conversion module (process computer). The go/no go signal generated by the WCAP- 17706-NP January 2013 16 Revision 0
bistable (analog) or the trip module (digital) is the output of the last module in the protection function process rack instrument loop and is the input to the voting logic.
" Rack Calibration Accuracy (RCA)
The two-sided (+) calibration tolerance of the process racks as reflected in the plant calibration procedures. The RCA is defined at multiple points across the calibration range of the channel, e.g., 0 %, 25 %, 50 %, 75 % and 100 % span for input modules, and specifically at the NTS for the bistable or trip module, see Figure 3-1. The RCA magnitude should be, and calibration procedure should confirm, the reference accuracy of the instrument process racks. Recording and trending of the As Left condition of the process racks (ALT = RCA) is necessary to assure conformance with the uncertainty calculation basic assumptions, i.e., random and two-sided.
For DCPP, the individual modules in a loop may be calibrated to a particular tolerance however, the process loop (as a string) is verified to be calibrated to a specific tolerance (RCA).
la.c This parameter is determined utilizing DCPP supplied information and the appropriate vendor specification document.
jac A periodic evaluation of RCA should be performed consistent with the requirements of Section 5.1.
- Rack Drift (RD)
The change in input-output relationship (As Found - As Left) over a period of time at reference conditions, e.g., at constant temperature.
]a~CRecording and trending of the As Found condition of the process racks (RD) is necessary to assure conformance with the uncertainty calculation basic assumptions.
This parameter is determined utilizing DCPP supplied information and the appropriate vendor specification document.
ac WCAP- 17706-NP January 2013 17 Revision 0
I ]I" A periodic evaluation of RD should be performed consistent with the requirements of Section 5.1.
" Rack Measurement & Test Equipment Accuracy (RMTE)
The accuracy of the test equipment (typically a transmitter simulator, voltage or current power supply, and DVM) used to calibrate a process loop in the racks. When the magnitude of RMTE meets the requirements of ANSI/ISA-51.l-1979 (R1993) (Reference 16, p. 61) it may be considered an integral part of RCA or RD. Uncertainties due to M&TE that are 10 times more accurate than the device being calibrated are considered insignificant and may not be included in the uncertainty calculations.
]ac
" Rack Reference Accuracy (RRA)
Rack Reference Accuracy is the "accuracy rating" as defined in ISA-51.1-1979 (Ri1993)
(Reference 16, page 12), specifically as applied to Note 2 and Note 3 for a process loop string.
The magnitude is typically defined in manufacturer's specification data sheets. Inherent in this definition is the verification of the following under a set of reference conditions; conformity (Reference 16, page 16), hysteresis (Reference 16, page 36) and repeatability (Reference 16, page 49).
The Invensys process racks have a self calibration feature that where it is noted that this feature includes the effects of the reference accuracy. Thus for these racks, the RRA term magnitude is set to 0 % span in the treatment of rack uncertainties.
a,c
- Rack Temperature Effects (RTE)
Change in input-output relationship for the process rack module string due to a change in the ambient environmental conditions (temperature, humidity), and voltage and frequency from the reference calibration conditions. It has been determined that temperature is the most significant, with the other parameters being second order effects. For process instrumentation, a typical value of [ ]` is used for the analog channel RTE which, based on design testing, allows for an ambient temperature deviation of+ 50 'F.
]aC This WCAP-17706-NP January 2013 18 Revision 0
parameter is determined utilizing DCPP supplied information and the appropriate vendor specification document.
]ax Range The upper and lower limits of the operating region for a device, e.g., 0 to 1200 psig for a Steam Line Pressure transmitter. This is not necessarily the calibrated span of the device, although quite often the two are close. For further information see ANSI/ISA-51.1-1979 (R1I993) (Reference 16).
- Readout Device Accuracy (READOUT) 0 The measurement accuracy of a special test, high accuracy, local gauge, digital voltmeter, or multimeter on its most accurate, applicable range for the parameter measured.
0 1/2/2 the smallest increment of an indicator, e.g., control board meter, i.e., readability.
- Safety Analysis Limit (SAL)
The parameter value identified in the plant safety analysis or other plant operating limit at which a reactor trip or actuation function is assumed to be initiated. The SAL is defined in Chapter 15 of the DCPP Updated Final Safety Analysis Report. Actual SAL values are determined, or confirmed, by review of the plant safety analyses. The SAL is the starting point for determination of the acceptability of the CSA, see Figure 3-1.
" Sensor Calibration Accuracy (SCA)
The two-sided (+) calibration tolerance for a sensor or transmitter as defined in the plant calibration procedures to be equivalent to the vendor specified reference accuracy. The SCA is defined at multiple points across the calibration range of the channel, e.g., 0 %, 25 %, 50 %, 75 %
and 100 % span. This parameter is determined utilizing DCPP supplied data with the transmitter model/range code information and the appropriate vendor specification document listed in Section 3.1 of WCAP- 17696-P (Reference 6). [
]a.c Westinghouse performed an evaluation of SCA consistent with the methodology identified in Section 4. A periodic evaluation of SCA should be performed consistent with the requirements of Section 5.1. The SCA magnitude should be, and the calibration procedure should confirm, the reference accuracy of the device. Based on Westinghouse recommendations for WCAP- I7706-NP January 2013 19 Revision 0
Resistance Temperature Detector (RTD) cross-calibration, this accuracy is typically []c for the Hot and Cold Leg RTDs.
" Sensor Drift (SD)
The change in input-output relationship (As Found - As Left) over a period of time at reference calibration conditions, e.g., at constant temperature. This parameter is determined utilizing DCPP supplied data with the transmitter model/range code information and the appropriate vendor specification document listed in Section 3.1 of WCAP-17696-P (Reference 6). Westinghouse performed an evaluation of SD consistent with the methodology identified in Section 4. [
]a.C A periodic evaluation of SD should be performed consistent with the requirements of Section 5.1.
- Sensor Measurement & Test Equipment Accuracy (SMTE)
The accuracy of the test equipment (typically a high accuracy local readout gauge and Digital Multimeter (DMM) used to calibrate a sensor or transmitter in the field or in a calibration laboratory. When the magnitude of SMTE meets the requirements of ANSI/ISA-51.l-1979 (R1993) (Reference 16, p. 61) it may be considered an integral part of SCA. Uncertainties due to M&TE that are 10 times more accurate than the device being calibrated are considered insignificant and may not be included in the uncertainty calculations.
]a,c
- Sensor Pressure Effects (SPE)
- The change in input-output relationship due to a change in the static head pressure from the calibration conditions for a Ap transmitter (level or flow).
- The accuracy to which a correction factor is introduced for the difference between calibration and operating conditions for a Ap transmitter (level or flow).
This parameter is calculated utilizing the transmitter model/range code information and the appropriate vendor specification document listed in Section 3.1 of WCAP-17696-P (Reference 6).
" Sensor Reference Accuracy (SRA)
As applied to a sensor or transmitter, the reference accuracy is the "accuracy rating" as defined in ISA-51.1-1979 (R1993)(Reference 16, page 12), specifically as applied to Note 2 and Note 3.
The magnitude is typically defined in manufacturer's specification data sheets. Inherent in this definition is the verification of the following under a set of reference conditions; conformity (Reference 16, page 16), hysteresis (Reference 16, page 36) and repeatability (Reference 16, page WCAP- 17706-NP January 2013 20 Revision 0
49). This parameter is determined utilizing the transmitter model/range code information and the appropriate vendor specification document listed in Section 3.1 of WCAP-17696-P (Reference 6).
Sensor Temperature Effects (STE)
The change in input-output relationship due to a change in the ambient environmental conditions (temperature, humidity), and voltage and frequency from the reference calibration conditions. It has been determined that temperature is the most significant, with the other parameters being second order effects. This term is typically limited to the effect due to temperature swings that occur at less than 130 'F. This parameter is calculated utilizing the transmitter model/range code information and the appropriate vendor specification document listed in Section 3.1 of WCAP-17696-P (Reference 6) [ ]ac
- Span The region for which a device is calibrated and verified to be operable, e.g., for a Steam Line Pressure transmitter, 1200 psi.
- Square Root Sum of the Squares (SRSS)
C = ý(al + (b / + (c As approved for use in setpoint calculations by ANSI/ISA-67.04.01-2006 (Reference 4).
- Total Allowance (TA)
The absolute value of the difference (in % instrument span) between the SAL and the NTS.
TA= ISAL-NTSI WCAP- I7706-NP January 2013 21 Revision 0
An example of the calculation of TA is:
PressurizerPressure - Low (Safety Injection)
SAL 1680.0 psig NTS -1850.0 psig TA 1-170.0 psi I 170.0 psi The instrument span = 2500 - 1250 psig = 1250 psi, therefore, TA = (170.O psi)* (100%span)_ 13.6 % span (250 psi)
- Trend The evaluation of [ ]ac on a periodic basis utilizing As Left and As Found plant data for SCA, SD, RCA and RD for each control, protection and indication function to verify that the statistically based assumptions of the uncertainty calculations are satisfied.
January 2013 I7706-NP WCAP- 17706-N-P January 2013 Revision 0 22
Safety Limit A SAL.
-4AI A 4 V M
Margin T +I( A NTS (LSSS)
A -A1,l --AVI Figure 3-1 Westinghouse Setpoint Parameter Relationship Diagram (Increasing Function)
WCAP-17706-NP January 2013 23 Revision 0
Table 3-1 AP Measurements Expressed in Flow Units The AP accuracy expressed as percent of span of the transmitter applies throughout the measured span, i.e., +/- 1.5 % of 100 inches AP = +/- 1.5 inches anywhere in the span. Because F 2 = f(AP) the same cannot be said for flow accuracies. When it is more convenient to express the accuracy of a transmitter in flow terms, the following method is used:
(FN) 2 = A PN Where: N = Nominal Flow 2 FN FN=aA PN
- Thus, aF A pjv Eq. 3-1.1 FN=2FN Error at a point (not in percent) is:
aFN '9AP, _ APN Eq. 3-1.2 2 2 FN 2(FN) ApN and 2
A PN (FN) 2 Eq. 3-1.3 A Pm. (F.a )
Where: max = maximum flow and the transmitter AP error is:
aAPN (100) percent error in Full Scale AP (% s FS AP)
Eq. 3-1.4 A Pmax WCAP- I 7706-NP January 2013 24 Revision 0
Table 3-1 (continued)
AP Measurements Expressed in Flow Units Therefore, aF, FEN L%
A Pmax.0 2APmax[ F' c FS F1r-PAP 100
]2
% EFSAP L(2)(100)
IF.ax 2 FEN Eq. 3-1.5 Error in flow units is:
%*FS APIIra
[F=F (2)(100)- JFN Eq. 3-1.6 Error in percent nominal flow is:
a2N (100) %EFSAP][Fm- j Eq. 3-1.7 2
FN L L EN]
Error in percent full span is:
aFN ( IO0)=
F][%_FSAP [Fm., (100)
Fmax FmaxL (2)(100) L FN Eq. 3-1.8 L2 LFNI Equation 3-1.8 is typically used to express errors in percent full span in Westinghouse uncertainty calculations.
WCAP- 17706-NP January 2013 25 Revision 0
4.0 WESTINGHOUSE CALIBRATION AND DRIFT EVALUATION PROCESS a,c WCAP- 17706-NP January 2013 26 Revision 0
a,c WCAP- 17706-NP January 2013 27 Revision 0
ac WCAP- 17706-NP January 2013 28 Revision 0
a,c WCAP-17706-NP January 2013 29 m* Revision 0
-7 ac WCAP- 17706-NP January 2013 30 Revision 0
a,C WCAP-17706-NP January 2013 3! Revision 0
ac WCAP- I7706-NP January 2013 32 Revision 0
a,c Figure 4-1 Westinghouse Calibration and Drift Data Evaluation Process Diagram WCAP- 17706-NP January 2013 33 Revision 0
5.0 APPLICATION OF THE WESTINGHOUSE SETPOINT METHODOLOGY 5.1 Uncertainty Calculation Basic Assumptions / Premises The equations noted in Section 2 are based on the following premises:
- 1. The instrument technicians make reasonable attempts to achieve the NTS as an As Left condition at the start of each process rack's surveillance interval, i.e., the calibration error is driven towards 0.0 % span.
- 2. The process rack calibration accuracy (As Left values) will be evaluated
]a., When combined with previous As Left values, the trend characteristics of that instrument channel can be determined. [
]a., of the calibration process and, thus, confirm the WSM uncertainty calculation assumption. The ability to calibrate is the first step in establishing the operability condition of the instrument channel. When a "leave alone zone" concept is incorporated into the calibration process, it is incumbent upon the DCPP staff to verify through the calibration trend evaluation process that a calibration bias is not introduced.
- 3. The process rack drift will be evaluated
]a,, Process rack drift is defined as the arithmetic difference between current As Found and previous As Left values. The recording of the first pass values in the increasing and decreasing span directions across the instrument span, when compared to the As Left values at the same points, determines the instrument drift. When combined with previous drift data for that instrument channel, the trend characteristics of drift for that channel can be determined. The instrument channel characteristics establish the performance of that channel. [
]ac The magnitude of drift for an instrument channel is the second indication of the operability condition of the channel.
- 4. The process racks, including the bistables for analog racks, are verified/functionally tested in a string or loop process.
- 5. The instrument technicians make reasonable attempts to achieve a small calibration error as an As Left condition at the start of each transmitter's surveillance interval, i.e., the calibration error is driven towards 0.0 % span.
- 6. The transmitter calibration accuracy (As Left values) will be evaluated
]1.c When combined with previous As Left values, the trend characteristics of that device can be determined. [ ]aC WCAP- 17706-NP January 2013 34 Revision 0
]*'C of the calibration process and, thus, confirm the WSM uncertainty calculation assumption. The ability to calibrate is the first step in establishing the operability condition of the device. When a "leave alone zone" concept is incorporated into the calibration process, it is incumbent upon the DCPP staff to verify through the calibration trend evaluation process that a calibration bias is not introduced.
- 7. The transmitter drift will be evaluated
]a.c Transmitter drift is defined as the arithmetic difference between current As Found and previous As Left values. The recording of the first pass values in the increasing and decreasing span directions across the instrument span, when compared to the As Left values at the same points, determines the transmitter drift. When combined with previous drift data for that device, the trend characteristics of drift for that device can be determined. The transmitter characteristics establish the performance of that transmitter. [
]a " The magnitude of drift for a transmitter is the second indication of the operability condition of the device.
It should be noted for (1) and (5) above that it is not necessary for the instrument technician to recalibrate a device or channel if the As Found condition is not exactly at the nominal condition, but is within the two-sided (+) ALT. As noted above, the uncertainty calculations assume that the ALT (conservative and non-conservative direction) is satisfied on a reasonable, statistical basis, not that the nominal condition is satisfied exactly. The evaluations above assume that the SCA, SD, RCA and RD parameter values are satisfied on at least a two-sided (+/-) 95 % probability / 95 % confidence level basis. Therefore, it is necessary for DCPP to periodically re-verify the continued validity of these assumptions. Westinghouse recommends that this verification be performed [ ]". This prevents the institution of non-conservative biases due to a procedural (or unwritten cultural) basis without the DCPP staff s knowledge and appropriate treatment.
In summary, a sensor/transmitter or process rack channel is considered to be "calibrated" when the two-sided (+/-) ALT is satisfied. An instrument technician may determine to recalibrate if near the extremes of the ALT, but it is not required. Recalibration is explicitly required any time the As Found condition of the device or channel is outside of the ALT. A device or channel may not be left outside the ALT without declaring the device or channel "inoperable" and appropriate action taken. Thus, an ALT may be considered as an outer limit for the purposes of calibration and instrument uncertainty calculations.
]a,c Thus, Westinghouse has concluded, that for operable process racks, AFT = ALT = RCA. With respect to WCAP- 17706-NP January 2013 35 Revision 0
sensor/transmitters, the AFT = SD, based initially on the vendor specification data and subsequently on the DCPP periodic evaluation of SD data (As Found - As Left).
The above results in the WSM's reliance on the NTS, and not the Limiting Trip Setpoint (LTSP) as defined in ISA-67.04.01-2006 (Reference 4) or the Limiting Setpoint (LSP) as defined in RIS 2006-17 (Reference 26). Specific to RIS 2006-17, the LSP is noted as: "... the limiting settingfor the channel trip selpoint (TSP) consideringall credible instrument errorsassociatedwith the instrument channel.
The LSP is the limiting value to which the channel must be reset at the conclusion ofperiodic testing to ensure the safety limit (SL) will not be exceeded if a design basis event occurs before the next periodic surveillance or calibration." As noted previously, with respect to the WSM, operability of the process racks is defined as the ability to be calibrated about the NTS (+/-ALT about the NTS) and subsequent surveillance should find the channel within the AFT = ALT about the NTS. On those rare occasions that the channel is found outside of the AFT = ALT, operability requirements would be initially satisfied via recalibration, or reset, about the NTS. Operability defined as conservative with respect to a zero margin LSP is a concept that is insufficient for the WSM, and is inconsistent with its basic assumption of the AFT = ALT = RCA definition. In order to have confidence (statistical or otherwise) of appropriate operation of the process racks, it is necessary that the process racks operate within the two-sided (+/-)
limits defined about the NTS. This is particularly true for protection functions that have historical NTS values that generate large margins. From a WSM perspective, systematic allowance of large drift magnitudes in excess of equipment design - either by large magnitude RD or RMTE terms or utilization of an LSP, generates a false sense of security which is inappropriate for future operation consideration, and which erodes the concept of performance based specifications and limits.
5.2 Process Rack Operability Assessment Program and Criteria The parameter of most interest as an indication of process rack operability is relative drift (As Found -
As Left) found to be within RD, where RD is the two-sided (+/-) 95/95 drift value assumed for that channel. However, this would require the instrument technician to record and have available in the field both the current As Found and the previous As Left condition data to perform a calculation in the field.
DCPP does not require that the previous As Left condition be ascertained prior to performance of a surveillance test and surveillance procedures are not set up for independent verification of calculations in the field.
An alternative for the process racks is the Westinghouse method for use of a fixed magnitude, two-sided
(+) AFT about the NTS. It would be reasonable for this AFT to be RMTE + RD, where RD is the actual statistically determined 95/95 drift value and RMTE is defined in the plant procedures. However, comparison of this value with the RCA tolerance utilized in the Westinghouse uncertainty calculations would yield a value where the AFT is less than the RCA tolerance (ALT).
pac WCAP-17706-NP January 2013 36 Revision 0
]a.c Therefore, a more reasonable approach for the plant staff to follow was determined. An AFT criterion based on an absolute magnitude that is the same as the RCA criterion, i.e., the allowed deviation from the NTS on an absolute indication basis is plus or minus (+/-) the RCA tolerance (ALT). A channel found inside the RCA tolerance (ALT) on an indicated basis is considered to be operable. A channel found outside the RCA tolerance (ALT) is evaluated and recalibrated. The channel must be returned to within the ALT for the channel to be considered operable. This criterion is incorporated into plant, function specific calibration and drift procedures as the defined ALT about the NTS.
]ac A channel found to exceed this criterion multiple times should trigger a more comprehensive evaluation of the operability of the channel. Thus, more elaborate evaluation and monitoring may be included, as necessary, if the drift is found to be excessive or the channel is difficult to calibrate.
5.3 Application of Process Rack Operability Assessment to the Plant Technical Specifications The drift operability criteria described for the process racks in Section 5.2 are based on a statistical evaluation of the performance of the installed hardware. These criteria
]a,c Sections 5.1 and 5.2 are consistent with the recommendations of the Westinghouse paper presented at the June 1994, ISA/EPRI conference in Orlando, FL (Reference 27). In addition, the plant operability assessment processes described in Sections 5.2 and 5.3 are consistent with the basic intent of ISA-67.04.01 (Reference 4). Therefore, the ALT and AFT magnitudes are "performance based" and are determined by adding (subtracting) the calibration accuracy (RCA = ALT = AFT) of the device tested during the Channel Operational Test to the NTS.
An example of the ALT and AFT calculations for the DCPP ALS process racks is:
WCAP- 17706-NP January 2013 37 Revision 0
PressurizerPressure- Low (Safety Injection)
ALT/AFT Determination NTS = 1850 psig SPAN = 1250 psi RCA = [ ]a ALT = NTS d RCA
(-) ALT =a AFT = NTS +/- RCA I axc
(+)AFT=
(-) AFT =[
5.4 Sensor/Transmitter Operability Assessment Program and Criteria The parameter of most interest for indication of transmitter operability is relative drift (As Found -
As Left) found to be within SD, where SD is the two-sided (+/-) 95/95 drift value assumed for that device.
However, this would require the instrument technician to record and have available in the field both the current As Found and the previous As Left condition data to perform calculations in the field. DCPP does not require that the previous As Left condition be ascertained prior to performance of a surveillance test and surveillance procedures are not set up for independent verification of calculations in the field.
An alternative for the transmitters is the very common method of use of a fixed magnitude, two-sided (+/-)
AFT about each of the nominal calibration points, e.g., 0 %, 25 %, 50 %, 75 % and 100 % span. Based on the As Found condition, operability of the device is determined as follows.
- 1. A transmitter found inside the SCA tolerance (ALT) about all calibration points, on an indicated basis, is considered to be operable and may be recalibrated.
- 2. A transmitter found outside the SCA tolerance (ALT) about one or more calibration point(s) but within the SD (AFT) at all of the calibration points is considered operable and must be recalibrated.
- 3. A transmitter found outside the SD (AFT) at three or more calibration point(s) is considered inoperable. A condition report should be initiated and the device must be recalibrated to demonstrate a return to an operable condition.
]a,c In all cases, for the device to be considered operable, the transmitter must be returned to within the ALT about all desired calibration points. This criterion is incorporated into DCPP, function specific calibration WCAP- 17706-NP January 2013 38 Revision 0
and drift procedures as the defined ALT about the desired calibration points. At a later date, once the As Found data is compiled, the relative drift (As Found - As Left) can be calculated and compared against the SD value. This comparison can then be utilized to ensure consistency with the assumptions of the uncertainty calculations, see Assumption 7. A transmitter found to exceed this criterion multiple times should trigger a more comprehensive evaluation of the operability of the device. Thus, more elaborate evaluation and monitoring may be included, as necessary, if the drift is found to be excessive or the transmitter is difficult to calibrate.
5.5 Application of the Sensor/Transmitter Operability Assessment The drift operability criteria described for transmitters in Section 5.4 are based on a statistical evaluation of the performance of the installed hardware. Thus, these criteria Pac Utilizing the approach of Section 5.4, ALT and AFT values for the transmitter would be defined at the multiple calibration points. An example is provided as follows.
January 2013 I7706-NP WCAP- I17706-NP January 2013 Revision 0 39
PressurizerPressure - Low (Safety hIjection)
ALT/AFT Determination SPAN = 1250 psi / 16 mA I ac Calibration Points = 0 %, 25 %, 50 %, 75 %, 100 % span Calibration zero = 1250 psig Calibration Points = 1250, 1562.5, 1875, 2187.5, 2500 psig ALT = Calibration Point +/- SCA a,c a,c 0 % span: (+) ALT = (-) ALT =
25 % span: (+) ALT = (-) ALT =
100 % span: (+) ALT = (-)ALT=
Equivalents, in mA or Volts, to the above ALT values would be found in the calibration procedure.
AFT = Calibration Point =LSD a,c axc 0 % span: (+) AFT = (-)AFT =
25 % span: (+) AFT = (-) AFT =
50 % span: (+) AFT = (-) AFT =
75 % span: (+) AFT = (-) AFT =
100 % span: (+) AFT = (-) AFT =
Equivalents, in mA or Volts, to the above AFT values would be found in the surveillance procedure.
WCAP- 17706-NP January 2013 40 Revision 0
6.0
SUMMARY
OF IMPORTANT POINTS Noted below is a summary of important points or assumptions with regards to the Westinghouse Setpoint Methodology.
- 1. The basic algorithm is an SRSS, accounting for M&TE dependency with the calibration or drift parameter.
- 2. Protection function uncertainty calculations are based on a single channel.
- 3. [
]ac
- 4. Westinghouse instrument uncertainties are two-sided.
- 5. [
],c
- 6. [
a,C
- 7. PMA terms provide allowances for the non-instrument related effects.
- 8. PEA term accounts for uncertainties due to metering devices, such as elbows, venturis, and orifice plates. In DCPP RTS/ESFAS uncertainty calculations, these are limited in application to flow measurements, e.g., RCS Flow (Cold Leg Elbow Taps) and Feedwater Flow.
- 9. The PEA term may be used for potential transformer characteristics for Undervoltage and Underfrequency applications.
- 10. The DCPP protection function CSA value is believed to be a two-sided 95 % probability at a 95 % confidence level (95/95) result.
- 11. The DCPP control function CSA value is believed to be a two-sided 95 % probability at a 95 %
confidence level (95/95) result.
- 12. [
a,c
- 13. The digital protection functions for DCPP provide a form/fit/function replacement for analog channels.
- 14. [ jac
- 15. Westinghouse reports CSA values to one decimal place using the technique of rounding down values less than 0.05 % span and rounding up values greater than or equal to 0.05 % span.
(+/-) about the NTS.
WCAP- 17706-NP January 2013 Revision 0 41
- 17. For transmitters, the AFT is a two-sided parameter (+/-) about the calibration points (absolute drift), or the AFT is a two-sided parameter (+/-) about the calibration recorded As Left points (relative drift).
- 19. For transmitters, the ALT is defined as the two-sided (+/-) SCA magnitude about the desired calibration points.
- 20. Margin is defined to be a non-negative number.
- 21. Westinghouse defines the NTS as the LSSS for the RTS and ESFAS functions listed in the DCPP Technical Specifications.
- 22. RCA is the random, two-sided (+/-) calibration tolerance of the process racks as reflected in the DCPP calibration procedures.
- 23. RCA is defined at multiple points across the calibration range of the channel, and specifically at the NTS for the bistable or trip module.
- 24. The RCA magnitude is, and the DCPP calibration procedure confirms, the reference accuracy of the instrument process racks.
- 25. Recording and trending of the As Left condition of the process racks (ALT = RCA) is necessary to assure conformance with the uncertainty calculation basic assumptions.
- 26. It is assumed that individual modules in a loop are calibrated to a particular tolerance and that the process loop (as a string) is verified to be calibrated to the RCA. [
]ac
- 27. Recording and trending of the As Found condition of the process racks (RD) is necessary to assure conformance with the uncertainty calculation basic assumptions.
- 29. The SAL is the starting point for determination of the acceptability of the CSA.
- 30. The two-sided (+/-) calibration tolerance for a sensor or transmitter (ALT) is defined in the DCPP calibration procedures.
- 31. The SCA is defined at multiple points across the calibration range of the channel.
- 32. The SCA magnitude is, and the DCPP calibration procedure confirms, the reference accuracy of the device.
- 33. Recording and trending of the As Left condition of the sensor or transmitter (SCA) is necessary to assure conformance with the uncertainty calculation basic assumptions.
- 34. Recording and trending of the As Found condition of the sensor or transmitter (SD) is necessary to assure conformance with the uncertainty calculation basic assumptions.
WCAP- I7706-NP January 2013 42 Revision 0
- 35. [
]a,c
- 36. [ ]a~c
- 37. [
]a.C 38.[
pac
- 39. [
axc
- 40. [
]a,c
- 41. Westinghouse will not pool data from multiple sites or different vendor hardware.
- 42. [
]a,c
- 43. [
- 44. [
Iac 45.
PC
- 46. [ ],C
- 47. The DCPP instrument technicians make reasonable attempts to achieve the NTS as an As Left condition at the start of each process rack's surveillance interval, i.e., the calibration error is driven towards 0.0 % span.
- 48. The process rack calibration accuracy (As Left values) will be evaluated
]a,c
- 49. The ability to calibrate is the first step in establishing the operability condition of the instrument channel.
WCAP-1 7706-NP January 2013 43 Revision 0
- 50. When a "leave alone zone" concept is incorporated into the calibration process, it is incumbent upon the plant staff to verify through the calibration trend evaluation process that a calibration bias is not introduced.
51.[
]ax
- 52. The recording of the first pass values in the increasing and decreasing span directions across the instrument span, when compared to the As Left values at the same points, determines the instrument drift. The magnitude of drift for an instrument channel/rack is the second indication of the operability condition of the instrument channel/rack.
- 53. The process racks, including the bistables, are verified/functionally tested in a string or loop process.
- 54. The DCPP instrument technicians make reasonable attempts to achieve a small calibration error as an As Left condition at the start of each transmitter's surveillance interval, i.e., the calibration error is driven towards 0.0 % span.
- 55. The transmitter calibration accuracy (As Left values) will be evaluated
]a,c
- 56. The ability to calibrate is the first step in establishing the operability condition of the device.
- 57. The transmitter drift will be evaluated p~c
- 58. The transmitter characteristics establish the performance of that transmitter. The magnitude of drift for a transmitter is the second indication of the operability condition of the device.
- 59. The operability evaluations assume that the SCA, SD, RCA and RD parameter values are satisfied on at least a two-sided (+/-) 95 % probability / 95 % confidence level basis. Therefore, it is necessary to periodically re-verify the continued validity of these assumptions. Westinghouse recommends verification [ ]a.c
- 60. The Westinghouse Setpoint Methodology relies on the NTS as the initial condition for process rack operability evaluations.
a*c 61."
- 62. Process rack ALT and AFT magnitudes are "performance based" and are determined by adding (subtracting) the calibration accuracy (RCA = ALT = AFT) of the device tested during the Channel Operational Test to the NTS.
- 63. Westinghouse has defined a three step transmitter operability evaluation process based on drift.
WCAP- 17706-NP January 2013 44 Revision 0
- a. If found inside the SCA tolerance (ALT) about all calibration points - the transmitter is considered to be operable and may be recalibrated.
- b. If found outside the SCA tolerance (ALT) about one or more calibration point(s) but within the SD (AFT) at all of the calibration points - the transmitter is considered operable and must be recalibrated.
- c. If found outside the SD (AFT) at three or more calibration point(s) - the transmitter is considered inoperable. A condition report should be initiated and the device must be recalibrated to demonstrate a return to an operable condition.
In all cases, for the device to be considered operable, the transmitter must be returned to within the ALT about all desired calibration points.
January 2013 I 7706-NP WCAP- 17706-NP January 2013 Revision 0 45
7.0 References
- 1. WCAP-1 1594 Revision 2, "Westinghouse Improved Thermal Design Procedure Instrument Uncertainty Methodology - Diablo Canyon Units I & 2, 24 Month Fuel Cycle Evaluation,"
Westinghouse Electric Company LLC, January 1997.
- 2. Regulatory Guide 1.105, Revision 3, "Setpoints for Safety-Related Instrumentation," Nuclear Regulatory Commission, December 1999.
- 3. Tuley, C. R., Williams, T. P., "The Significance of Verifying the SAMA PMC 20.1-1973 Defined Reference Accuracy for the Westinghouse Setpoint Methodology," Instrumentation, Controls and Automation in the Power Industry, Vol. 35, Proceedings of the Thirty-Fifth Power Instrumentation Symposium (2 nd Annual ISA/EPRI Joint Controls and Automation Conference),
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II. Westinghouse letter NS-TMA-1835, "American Electric Power Project, Donald C. Cook Unit 2 (Docket 50-316), Westinghouse Reactor Protection System/Engineered Safety Features Actuation System Setpoint Methodology," Westinghouse Electric Company LLC, June 1978.
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AP1000," Westinghouse Electric Company LLC, May 2006.
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WCAP- 17706-NP January 2013 46 Revision 0
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- 17. [ ]8,C
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- 23. [
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2 Microsoft and Excel are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries WCAP- 17706-NP January 2013 47 Revision 0