ML20154H111
| ML20154H111 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 05/19/1988 |
| From: | Cockfield D PORTLAND GENERAL ELECTRIC CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8805250228 | |
| Download: ML20154H111 (12) | |
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Fortland General ElectricCompany I
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David W. Cockfield Vice President. Nuclear May 19, 1988 Trojan Nuclear Plant Docket 50-344 License NPF--I U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington DC 20555
Dear Sir:
TROJAN NUCLEAR PLANT Licenso Change Application (LCA) 145, Revision 1 Pressure and Differential Pressure Transmitter Setpoint Changes As s. result of Nuclear Regulatory Commi"Jion staff review, addillonal information in the Significant Hazards Determination for LCA 145 was requested. In addition, Portland Ceneral Electric was evaluating the model of transmitters to use in several applications and needed to reconsider the setpoints submitted in Revision 0 to LCA 145. This effort has been completed. Attached is a revised LCA 145, including the revised Significant Hazards Considerations discussion, to replace the LCA 145 submitted on October 28, 1986. Changes are indicated by a vertical line in the right-hand margin.
Sincerely, Attachment c: Mr. John B. Martin Regional Administrator, Region V.
U.S. Nuclear Regulatory Commission Mr. Bill Dixon State of Oregon Department of Energy Mr. R. C. Barr NRC Resident Inspector Trojan Nuclear Plant 8805250228 880519 PDR ADOCK 05000344 I P DCD i
121 S W STTon Eteet Pccant Owyn 97204
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LCA 145, Rsv. l' l
Attachment A page 1 of 9 Reason for Change The Trojan Final Safety Analysis Report (FSAR) and Technical Specifications provide steam generator low-low level reactor trip / auxiliary feedwater pump start and pressurizer low-pressure safety injection setpoints established by the original Plant design. Interim setpoints had been in use.for several years to account for additional instrument inaccuracies that became known subsequent to Plant startup. Reference leg heating effects and vendor [
transmitter defect notifications were major contributors to these increased inaccuracies.
Subsequent improvements to the pressure transmitters, plus insulation of I reference legs on the steam generator level instruments, had resulted in reduced inaccuracles and thus reduced setpoints and allowable values.
However, those values still remained greater than those cited in the Technical Specifications.
Reference 1 committed to revise the Technical Specification values once the improvements noted above were complete.
License Change Application (LCA) 145 was initially submitted to the Nuclear Regulatory Connission (NRC) on October 28, 1986. During review of LCA 145, the NRC determined that additional information was required, with regard to '
the significant hazarde determination, to complete the review. Portland General Electric (PGE) was requested by phone call in January 1987 to provide- ;
a more quantitative description of the sotpoint history and uncertainties, including improvements in the uncertainties as a result of modifications.
This information was to be included in a revised significant hazards determination. Ptior to submittal of the revised significant harards determination, the pressurizer low-pressure safety injection setpoint was !
discovered to be in error.
The error was due to the exclusion of harsh environment current leakage from the setpoint calculations. The original Trojan specific setpoint methodology 1 (Reference 2) considered the error contribution from this current leakage to l be insignificant. For this reason, it was not included in the previous setpoint calculations. Subsequently in 1987, PGE determined that harsh I environment cable current leakage was a significant centributor to the overall loop instrumentation uncertainty used in determining reactor protection setpoints for functions that need to actuate in a harsh environment. The steam generator low-low level reactor trip, the pressurizer low-pressure safety injection functions both need to be able to activate in a harsh environment. These setpoints were recalculated to include the harsh environment current leakago.
The inclusion of the leakage error in the setpoint calculations resulted in an increase in the pressurizer low-pressure safety injection setpoint. The steam l
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LCA 145, Rsv. 1 Attachment A Page 2-of 9 generator low-low level reactor trip setpoint remained unchanged since sufficient margin was available to account for the current leakage.
Description of Channe New setpoints and allowable values have been calculated for the steam generator low-low water level reactor trip / auxiliary feedwater pump start, and pressurizer low-prossure safety injection. They are based, in part, upon the following icprovements provided by the pressurizer pressure and steam generator level transmitter vendor:
- 1. Elimination of thermal repeatability errors and Loss-of-Coolant-Accident (LOCA) thermal errors.
- 2. Elimination of negative shift errors.
- 3. Use of Barton-supplied environmental allowance value of 5.59 percent of span, based on their evaluation of qualification results against Trojan-specific LOCA profile for temperatures and PGE's conclusion that other synergistic effects are not significant in the interval of concern.
The causes of the thermal nonrepeatability errors were identified as a leakage path from the circuit to case ground through the zero and span potentio-meters, and incorrect manufacturing methodology used during the temperature compensation process. The corrective actions were the addition of isolation washers between the potentiometer mounting bracket and the potentiometers to isolate them from case ground, and revision to the temperature compensation procedures. The corrective actions have been implemented at the vendor and l all transmitters shipped after January 1, 1983 meet the original published ;
performance specifications.
The negative shift errors were the results of the combined creep of: (1) the link wire connecting the pressure sensing bourdon tube with the strain gauge beam, and (2) the link wire attachment material. In addition to correcting the creep problem, changes have been made to the method of mounting and controlling the amount of deflection of the strain gauge beam, and to the location of an insulating pad for the termination of the lead wires of the t strain gauge. SubsequenL testing has shown the above changes result in performance within spccification limits. Instruments delivered af ter the defect identification incorporate the changes.
In addition, increased securacy of the steam generator low-low level reactor trip, due to insulation of steam generator level detector reference legs in 1985, was incorporated into the same calculation.
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LCA 145, Rtv. 1 Attachment A Page 3 of 9 1
The resultant changes to Technical Specification Tables 2.2-1 and 3.3-4, including the interim and the revised setpoints are:
Steam Generator Low-Low Pressurizer Low-Pressure Level Reactor Trip (%) Safety Injection (PS!G)
(Table 2.2-1) (Table 3.3-4)
Setpoint Allowable Setpoint Allowable Current Technical Specification Value 15 14 11765 11755 (Original License)
Interim Value 102 N/A 11831 N/A (1983)
LCA 145, Rev. 0 111 110 11766 11759 (1986)
LCA 145, Rev. 1 111 110 11773 11765 (1988)
Safety Evaluation This proposed LCA modifies the Trojan Technical Specification regarding new setpoints for the steam generator low-low water level reactor trip and pressurizer low-pressure safety injection. The proposed changes are to Section 2.0, Table 2.2-1 and associated bases, and section 3.0, Table 3.3-4 of the Technical Specifications.
Trojan was previously operating on interim conservative setpoints that were established in 1979 due to steam generator reference leg heatup errors and subsequently revised in 1983 due to inaccuracies in the new recently installed transmitters. These interim setpoints were determined from information supplied by the Nuclear Steam Supply System (NSSS) vendor in order to ensure that the original safety analysis was still bounding. '
PGE calculated new setpoints caused by the replacement transmitters based upon reference leg insulation and transmitter improvements provided by the vendor.
Subsequent to PGE's calculations of the new setpoints, it was determined that harsh environment cable current leakage made a significant contribution to the instrumentation error. The setpoints were recalculated during the 1987 outage )
to include the current leakage error. This resulted in an increase in the pressurizer low-pressure safety injection sotpoint over that calculated in l 1986. The steam generator low-low level reactor trip setpoint did not change since sufficient margin was available in the original setpoint to compensate ;
for the additional inaccuracy. I I
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- .LCA 145, R:v. 1 Attachment A page 4 of 9 In accordance with Title 10, Code of Federal Regulations 50.59 (10 CFR 50.59),
LCA 145 is judged to involve no unreviewed safety question based on the ;
following: '
- l. The proposed setpoints of the LCA do not increase the probability of occurrence or the consequences of an accident or malfunction _of equipment ;
important to safety previously evaluated in the safety analysis report.
The purpose of the steam generator low-low water level reactor trip ;
, setpoint is to trip the reactor upon a loss of heat sink. The purpose of the pressurizer low-pressure safety injection setpoint is to trip the reactor and actuate the Engineered Safety Features during a LOCA. The steam generator low-low water level setpoint also provides a signal to automatically start the auxiliary feedwater pumps. The new setpoints for these replacement transmitters accommodate steam generator refere lee heatup and other accident-induced environmental errors not accon
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in the originally licensed setpoints or considered in the origi, and still bounding safety analysic.
Trojan's accident analysis assume setpoints of 0 percent of span for the steam generator low-low level trip and 1700 psig for the pressurizer low-pressure safety injection. The new Technical Specification limits ensure these assumed values will not be exceeded. The new limits take into consideration instrument uncertainty, circuit loop uncertainty, and the harsh environment induced uncertainty. These new-setpoints are less limiting than the interim setpoints; yet provide the margin necessary to ensure plant protection consistent with the FSAR analyses. In addition, they provide greater flexibility for transient conditions, thereby minimizing the likelihood of inadvertent protective action and challenges to the plant safety systems.
To ensure that the setpoints assumed in the safety analysis are not exceeded, a Channel Statistical Allowance (CSA) is determined for the actual setpoint. The major contributor to the CSA is the environmental allowance. The environmental allowance, in addition to the vendor defect notifications referenced previously in this LCA, prompted pGE to establish conservative interim setpoints until transmitter replacement could be accomplished.
During the 1986 outage, the transmitters were replaced with functionally equivalent components, supplied by the vendor, that are less susceptible to adverse environmental conditions. The transmitter vendor provided a plant-specific environmental allowance value of 5.59 percent of span based on the Trojan LOCA Containment temperature profile. The setpoints were then changed to the current values, to reflect this improvement, during the 1986 refueling outage. Subsequently, in 1987, it was determined that the error contribution due to harsh environment cable current leakage was more significant than had been indicated by the original Trojan specific l i
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" LCA 145, Rsv. 1 Attachment A-Page 5 of 9 4
setpoint methodology. The reactor protection setpoints were recalculated to include this current leakage contribution to the environmental
, allowance portion of the CSA. This resulted in a 7 psig increase in the pressurizer low-pressure safety injection satpoint and no change in the steam generator low-low level reactor trip setpoint. Table 1 provides a chronology for the setpoints including the changes in the environmental allowance which accounted for the reduction from the interim setpoints to the current values.
In conclusion, the new setpoint values have been increased over those originally licensed to incorporate the environmental allowance, and provide assurance of reactor-protection system actuation prior to exceeding the limits established in the safety analyses. The original safety analysis was bounding for the interim setpoints and is still bounding for the new setpoints. Thus, there is not increase in probability or consequences of a previously evaluated accident.
- 2. This proposed LCA does not create the possibility for an accident or malfunction of a different type than any evaluated previously in the safety analysis report.
The only change to the Plant or its operation is in the setpoints themselves. The transmitter changeout did not involve any changes to the Plant protection system or associated circuitry. The original transmitters were replaced with functionally equivalent components with less susceptibility to environmental conditions. The adjustment of the setpoints to more restrictive limits to incorporate the environmental ;
allowance and the harsh environment cable current leakage error, does not '
create the possibility of a new or different kind of malfunction or accident.
- 3. This proposed LCA does not result in a reduction in any margin of safety as defined in the basis for any Technical Specification.
i The originally licensed setpoints did not make allowance for adverse environment induced inaccuracies. In addition, the new setpoints provide for improved operating margin and Plant availability over those used in the interim. The interim setpoints were set conservatively high to provide protective margins and ensure that the original safety analysis would continue to be bounding until the transmitters could be replaced I
with the improved models. The consequences of continued operation with j the overly conservative interim setpoints would be an increase in the- '
probability of inadvertent actuation of the protective functions, due to a reduction in operating margin. This is especially true for steam -
I generator water level control during startup and shutdown. Inadvertent reactor trips reduce Plant availability and provide unnecessary challenges to Plant protection systems.
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1 LCA 145, Rsv. 1 '
Attachment A Page 6 of 9 The new setpoints improve the margin of safety by incorporating the effect of environmental, including harsh environment-cable current leakage errors, on the process signals. The setpoints were increased from those-originally licensed and used in the accident analysis, and operating margin is improved over that provided by the interim setpoints. The original safety analysis is still bounding; therefore, this proposed LCA does not involve a reduction in a margin of safety.
No physical changes in the Plant design or operation are proposed. The new setpoints provided improved Plant protection by accounting for inaccuracies in the process signals and, thus, provide improved margins.' Other than changing calibration setpoints, Plant procedures are not affected.
For these reasons, it is PCE's determination that the proposed change does not involve an unreviewed safety question. -
Significant Hazards Determination This proposed LCA modifies the Trojan Technical Specification regarding new l setpoints for the steam generator low-low water level reactor trip and pressurizer low-pressure safety injection protective functions. The proposed changes are to Section 2.0, Table 2.2-1 and associated bases, and Section 3.0, Table 3.3-4 of the Technical Specifications. '
Trojan was previously operating on interim conservative setpoints that were established in 1979 due to steam generator reference leg heatup errors and subsequently revised in 1983 due to inaccuracies in recently installed transmitters. These interim setpoints were determined from the Trojan specific setpoint methodology and information supplied by the NSSS vendor in order to ensure that the original safety analysis was still bounding.
PGE calculated new setpoints caused by the replacement transmitters based upon reference leg insulation and transmitter improvements provided by the vendor.
Subsequent to pCE's calculations of the new setpoints, it was determined that harsh environnent cable current leakage made a significant contribution to the
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instrumentation error. The setpoints were recalculated during the 1987 outage j to include the current leakage error. This resulted in an increase in the i
pressurizer low-pressure safety injection setpoint over that calculated in l 1986. The steam generator low-low level reactor trip setpoint did not change
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since sufficient margin was available in the original setpoint to account for !
the additional inaccuracy.
2 In accordance with 10 CFR 50.92, LCA 145 is judged to involve no significant I hazards considerations based on the following:
] 1. The proposed setpoints of the LCA do not significantly increase the 1
probability or consequences of an accident previously evaluated. !
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LCA 145 RLv. 1 Attachment A Page 7 of 9 The purpose of the steam generator low-low water level reactor trip setpoint is to trip the reactor upon a loss of heat sink. The purpose of the pressurizer low-pressure safety injection setpoint is to trip the reactor and actuate the Engineered Safety Features during a LOCA. The steam generator low-low water level setpoint also provides a signal to automatically start the auxiliary feedwater pumps. The new setpoints for the replacement transmitters accommodate steam generator reference leg heatup and other accident-induced environmental errors not accounted for in the originally licensed setpoints or considered in the original and still bounding safety analyses.
Trojan's accident analyses assume setpoints of 0 percent of span for the steam generator low-low level trip and 1700 psig for the pressurizer low-pressure safety injection. The new Technical Specification limits ensure these assumed values will not be exceeded. The new limits take into consideration instrument uncertainty, circuit loop uncertainty, and the harsh environment induced uncertainty. These new setpoints are less limiting than the interim setpoints; yet provide the margin necessary to ensure Plant protection consistent with the FSAR analyses. In addition, they provide greater flexibility for transient conditions, thereby minimizing the likelihood of inadvertent protective action and challenges to the Plant safety systems.
To ensure that the setpoints assumed in the safety analysis are not exceeded, a CSA is determined for the actual setpoint. The major contributor to the CSA is the environmental allowance. The environmental allowance, in addition to the vendor defect notifications referenced previously in this LCA, prompted PGE to establish conservative interim setpoints until transmitter replacement could be accomplished.
During the 1986 outage, the transmitters were replaced with functionally equivalent components, supplied by the vendor, that are less susceptible to adverse environmental conditions. The vendor provided a Plant-specific environmental allowance value of 5.59 percent of span based on the Trojan LOCA Containment temperature profile. The setpoints were then changed to the current values, to reflect this improvement, during the 1986 refueling outage. Subsequently, in 1987, it was determined that the error contribution due to harsh environment cable current leakage was more significant than had been indicated by the original Trojan specific setpoint methodology. The reactor protection setpoints were recalculated to include the current leakage contribution. This resulted in a 7 psig increase in the pressurizer low-pressure safety injection setpoint. Table 1 provides a chronology for the setpoints including the changes in the environmental allowance which accounted for the reduction from the interim setpoints to the current values.
, LCA 145, R v. 1 Attachment A Page 8 of 9 In conclusion, the new setpoint values have been increased over those originally licensed to incorporate the environmental allowance, and provide assurance of reactor protection system actuation prior to exceeding the limits established in the safety analyses. The original safety analysis was bounding for the interim setpoints and is still bounding for the new setpoints. Thus, there is no increase in probability or consequences of a previously evaluated accident.
- 2. This proposed LCA does not create the possibility of a new or different kind of accident from any accident previously evaluated.
The only change to the Plant or its operation is in the setpoints themselves. The transmitter changeout did not involve any changes to the Plant protection system or associated circuitry. The vendor transmitters were replaced with functionally equivalent components with less susceptibility to adverse environmental conditions. The adjustment of the setpoints to more restrictive limits to incorporate the environmental allowance, including the harsh environment cable current leakage error, does not create the possibility of a new or different kind of accident.
- 3. This prorised LCA does not involve a significant reduction in a margin of safety.
The originally licensed setpoints did not make allowance for environmental effects or harsh environment cable current leakage error. In addition, the new setpoints provide for improved operating margin and Plant availability over those used in the interim. The interim setpoints were set conservatively high to provide protective margins and ensure that the original safety analysis would continue to be bounding until the transmitters could be replaced with the improved models. The consequences of continued operation with the overly conservative interim setpoints would be an increase in the probability of inadvertent actuation of the protective functions, due to a reduction in operating margin. This is especially true for steam generator water level control during startup and shutdown. Inadvertent reactor trips reduce Plant availability and provide unnecessary challenges to Plant protection systems.
The new setpoints improve the margin of safety by incorporating the ef fect of environmental, including harsh environment cable current leakage errors, on the process signals. The setpoints were increased from those originally licensed and used in the Trojan Safety Analysis, and operating margin is improved over that provided by the interim setpoints. The original safety analysis is still bounding; therefore, this proposed LCA does not involve a significant reduction in a margin of safety.
Guidance concerning the application of the three standards of 10 CFR 50.92 addressed above is provided by 48 FR 14870 which lists examples that may/may I
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i ' LCA 145,'Rsv. 1 Attachment A Page 9 of 9 not involve significant hazards considerations. Example 2 of amendments that are considered not likely to involve significant hazards considerations applies to the changes proposed herein and states:
"A change that constitutes an additional limitation, restriction or control not presently included in the Technical Specifications, e.g., a more stringent surveillance requirement."
No physical changes in the Plant design or operation are proposed. The new setpoints provide improved Plant protection by accounting for inaccuracies in indication and, thus, provide improved operating margins. l For these reasons, it is PGE's determination that the proposed change does not involve a significant hazards consideration.
References
- 1. PGE (B. D. Withers) to NRC (J. B. Martin) letter concerning Barton transmitter setpoint changes dated November 30, 1984.
- 2. Westinghouse Setpoint Methodology for Protection Systems, August 1984. l 2638P
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- TROJAN SETr) INT HISTORY ' ,
Steam Generator Low-Low Water Level Reactor Trip Setpoint Ssfaty Originally New Proposed Technical Analysis Licensed Specification Value Assumption (Present Interim - Prior to Interim - Post Before Inclusion of New Proposed Technical-(FSAR Technical Reference Leg Reference Leg Current Leakage Error Specification Value Chaptar 15) Specification) Insulation (1985) Insulation (1985) LCA 145.'Rev. O (1986) LCA 145. Rev. 1 (1988) g O percent > 5 percent of _
> 20 percent of span g 15 percent of 1 11 percent of span 1 11 percent of cf spin span span span
[a]EA = 0 [a]EA = 16.23 percent ta]EA = 11.22 percent [a,c]EA = 6.81 percent The steam generator of span or 83 percent of span or 77 percent of span or 67 percent low-low water level The 5 percent of the CSA.[b] of the CSA.[b] of the CSA.ID} setpoint was not of span is affected by the comprised of Reference leg contri- Referfence leg con- Reference leg con- current leakage in the the instrument bution to EA is 6.23 tribution to EA is tribution to EA is calculation. The margin effects listed percent. 1.22 percent. 1.22 percent. available in the CSA l in [b] below; determination in l however, it dif- Other instrument CSA = 3.32 + 11.22 = Vendor supplied EA LCA 145, Rev. O was j fers from the errors contribute 14.54(15), the decimal for new transmitters sufficient to account l new values of 3.32 percent of is rounded up. is 5.59 percent of' for this additional i Channel Sta- span.Ib] span. Total . error. The setpoint I
tistical EA = 5.59 + 1.22 = 6.81. remains at 1 11 percent .
Allowance CSA = 3.32 + 16.23 = of span.
(CSA) due to 19.55(20), the decimal CSA = 3.32 + 6.81 =
l calculation is rounded up. 10.13(11), the decimal methodology. is rounded up.
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[o] EA = Environmental Allowance. This allowance was not accounted for in the originally licensed setpoints.
[b] Channel Statistical Allowance (CSA) is the sum of Environnontal Allowance, harsh environment current leakage, and the square root of the sum of the squares of process measurement accuracy, sensor calibration, sensor pressure'and l temperature effects, sensor drift, rack calibration accuracy, comparators, rack temperature effects, and rack drift.
l The CSA is calculated using the methodology presented in Reference 2.
[c] The relationship between the Setpoint and Environmental Allowance is linear and thus allows a one-to-one reduction.
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Pressurizer Low-Pressure Safety Injection Setpoint S:fsty Originally New Proposed Technical ,
Anslysis Licensed Specification Value Ascumption (Present Interim - Post Before Inclusion of New Proposed Technical (FSAR Technical Vendor Defect Current Leakage Error Specification Value Chrpter 15) Specification) Notice (1983) LCA 145. Rev. 0 (1986) LCA 145. Rev 1 (1988) g 1700 psig 1 1765 psig g 1831 psig g 1766 psig 1773 psig
[a]EA = 0 [a]EA = 13.7 percent [a,c]EA = 5.59 percent of [a]EA = 5.59 percent of of span (span = 800 span for the new vendor span.
psig). transmitters.
Other instrument errors Other instrument errors Other instrument errors contribute 2.60 percent contribute 2.60 percent contribute 2.60 percent of span, of span. of span.
[b]CSA = 13.7 + 2.60 = CSA = 5.59 + 2.60 = 8.20 Current leakage con-16.3 percent of span or percent of span or 66 psig. tributes 0.89 percent 131 psig. of span.[d]
CSA = 5.59 + 2.60 + 0.89 =
9.08 percent of span or 73 psig.
[o] EA - Environmental Allowance. This allowance was not accounted for in the originally licensed setpoints.
[b] Channel Statistical Allowance (CSA) is the sum of Environmental A11cwance, harsh environment current leakage, and the square root of the sum of the squares of process measurement accuracy, sensor calibration, sensor pressure and temperature effects, sensor drif t, rack calibration accuracy, comparators, rack temperature effects, and rack drif t.
The CSA is calculated using the methodology presented in Reference 2.
[c] The relationship between the Setpoint and Environmental Allowance is linear.and thus allows a one-to-one reduction.
[d] Harsh Environment Current Leakage is treated as part of the Environmental Allowance portion of the CSA and is linearly.
Edded in the overall allowance determination.
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