ML20211D132
| ML20211D132 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 08/20/1999 |
| From: | Langenbach J GENERAL PUBLIC UTILITIES CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20211D136 | List: |
| References | |
| 1920-99-20295, NUDOCS 9908260183 | |
| Download: ML20211D132 (2) | |
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GPU Nuclear, Inc.
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Route 441 South l
NUCLEAR Post Office Box 480 Middletown. PA 17057-0480 Tel 717-944 7621 August 20,295 1999 1920-99-20 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington,IX' 20555
Dear Sir:
Subject:
Three Mile Island Nuclear Generating Station, Unit 1 (TMI-1) l Operating License No. DPR-50 Docket No. 50-289 l
Technical Specification Change Request No. 283, j
l Degraded Grid Undervoltage Relay Setpoint Calibration Frequency and j
Degraded Voltage Relay Tolerance Revision l
Pursuant to 10 CFR 50.4(b)(1), enclosed is TMI-l Technical Specification Change Request (TSCR) No. 283. The purpose of this TSCR is to request approval for a revision of the 4KV Engineered Safeguards Bus Undervoltage Relay Degraded Voltage calibration interval from refueling to annual and a change to the facility Technical Specification bases which revises the degraded voltage relay as-left setpoint tolerances as described in Enclosure 1.
Approval of the bases change is being requested since this change in effect changes the tolerance band for the degraded voltage relays. In addition, changing the tolerance for the relays, the latest analysis identifies the need for earlier operator action to prevent separation from the grid for some conditions and identifies additional safety related components that could be operated outside the i
normal voltage tolerance bands. Thejustification for operation of the components outside the normal band is described in this request.
Using the standards in 10 CFR 50.92, GPU Nuclear has concluded that these proposed changes do not constitute a significant hazards consideration, as described in the enclosed analysis i
performed pursuant to 10 CFR 50.91(a)(1). Also enclosed is a Certificate of Service for the l
request, certifying service to the chief executives of the township and county in which the facility [
is located, as well as the designated oflicial of the Commonwealth of Pennsylvania, Bureau of 9
Radiation Protection.
I N
gO Sincerely,
' b1@
9908260183 990820 PDR ADOCK 05000289
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P PDR James W. Langenbach Vice President and Director, TMl I
r 1920-99-20295 Page 2 of 2 j
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Enclosures:
(1) Technical Specification Change Request No. 283 (2) Proposed Revised Technical Specification and FSAR Pages (3) Cenificate of Service for Technical Specification Change Request No. 283 cc:
Administrator, Region 1 - Huben J. Miller TMI Senior Resident Inspector - Wayne L. Schmidt TMl-1 Senior Project Manager - Timothy G. Colburn File 99096 4
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1920-99-20295 METROPOLITAN EDISON COMPANY JERSEY CENTRAL POWER AND LIGHT COMPANY PENNSY'LVANIA ELECTRIC COMPANY AND GPU NUCLEAR INC.
Three Mile Island Nuclear Station, Unit 1 Operating License No. DPR-50 Docket No. 50-289 Technical Specification Change Request No. 283 COMMONWEALTH OF PENNSYLVANIA
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COUNTY OF DAUPHIN
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This Technical Specification Change Request is submitted in support of Licensee's request to change Appendix A to Operating License No. DPR-50 for the Three Mile Island Nuclear Station, Unit 1. As part of this request, proposed replacement pages for Appendix A are also included.
All statements contained in this submittal have been reviewed, and all such statements made and matters set forth therein are true and correct to the best of my knowledge.
GPU NUCLEAR INC.
BY:
Udd M
[J ice President and or, TMI f
Sworn and subscribed before me this 20th day of August
,1999, D
.b Y Ndary Public Notariai seal Melody Kim Kulp, Notary Public kcdinmTsN7xpies Au f,"2 1
Member, Pennsylvania Association o! ' canes
1920-99-20295 Technical Specificteian Change Request No. 283, Degraded Grid Undervoltage Relay Setpoint Calibration Frequency and Degraded Voltage Relay Tolerance Revision 1
1920-99-20295 Page 1 of 8 I.
. TECHNICAL SPECIFICATION CHANGE REOUEST (TSCR) NO. 283 GPU Nuclear requests that the following changes be made to Table 4.1-1, Item 43 a. of the TMI-l Technical Specifications (TSs) and the bases of Section 3.5.3:
Replace the existing TS pages 3-37a and 4-7 with the revised pages.
11.
REASON FOR CHANGES The purpose of this TSCR is t.o obtain a license amendment allowing 1) revision of the 4KV Engineered Safeguards Bus Undervoltage Relay Degraded Voltage calibration to be performed at an annual interval rather than its present refueling interval and 2) the bases are changed to state that the degraded voltage relay setpoint tolerance is being changed from an "as left" reading to an "as found" reading.
Calculation C-1101-700-E510-010,"TMI-l AC Voltage Regulation Study"(the calculation) was issued to replace Technical Data Report (TDR) 995, Revision 3. The new calculation employed a more rigorous methodology to determining undervoltage relay tolerances and included analyses of previously unconsidered loads and non-motor loads. As a consequence of these differences, a tighter degraded voltage relay as-left tolerance is needed to achieve better relay accuracy and a reduction in the possibility of separation of the engineered safeguards (ES) buses from the offsite power source. The more restrictive assumptions for calibration interval were used to determine degraded voltage relay tolerances in the calculation. Therefore the TS should be revised to establish an annual calibration interval for the Degraded Voltage Relays.
Additionally, the new calculation identified a need to compensate for the lack of voltage margin through reliance on manual action in lieu of full automatic voltage protection, as implied by Chapter 8 of the Updated Final Safety Analysis Report (UFSAR). Such actions, to improve voltage and thereby protect NSR loads, would involve load manipulations following a LOCA with post LOCA conditions in combination with extremely low switchyard voltage.
A revision has been proposed to USAR Chapter 8 Sections 8.1. 8.2.2.2 to make the voltage protection description consistent with the possibility that manual actions may be required to restore adequate voltage in the long term following a LOCA: in order to assure adequate voltage to NSR loads. Revised USAR pages 8.2-3 and 8.2-5 are provided in Enclosure 2.
Ill. SAFETY EVALUATION JUSTIFYING CHANGES 5
The function of the degraded voltage relays is to provide a second level of undervoltage 3
protection for the ES buses in the event of a low voltage event that does not develop into a complete voltage collapse. The relays feature two settings, pickup and dropout, which are adjustable by fixed taps as well as internal adjustment potentiometers. The dropout setting
1920-99-20295 Page 2 of 8 determines the value that the output contacts will transfer on decreasing voltage. The pickup setting, also referred to as the reset setting, determines the value that the output contacts will transfer on increasing voltage.
ES buses ID and IE are each provided with three degraded voltage relays, one per phase, which are WYE connected to the potential transformer secondary. The output contacts of the relays, which close on low bus voltage, are connected to a two out of three logic scheme, such that the simultaneous occurrence ofvoltage below the relay setpoint on two out of three relays will initiate a 10 second timer (27XCTD,27XETD). If the voltage on at least two of the relays does not recover to the pickup setpoint before the time delay relay times out, the affected bus will be disconnected from its offsite power source.
The calculation, determined relay setpoint tolerances which, along with the nominal dropout and pickup setpoints, define the limits ofoperating voltages for the relays, and hence the range of voltage that could occur on the ES buses without automatic separation frorn the offsite power source. Separation could occur either due to sustained low bus voltage below the dropout setpoint, or failure of bus voltage to recover to the higher pickup setpoint
' following a transient dip below the dropout setpoint. It is necessary to set the relay dropout at least high enough to protect nuclear safety related (NSR) loads, but it is also desirable to set the pickup as low as possible to make it easier for the relay to reset following voltage dips, thus preventing undesired separation from the offsite power source.
The existing nominal dropout setpoint of 3760 V was retained as a basis for calculations, as it proved to be a reasont.ble compromise between the critical voltage and reset voltage constraints. The minimum relay deadband ratio recommended by the relay manufacturer of 100.5% was applied to the dropout setting (3760 V) resulting in a proposed nominal pickup setting of 3779 V vs. the existing setpoint range of 3778 V to 3811 V. When appropriate tolerances were applied to these setpoints, a minimum dropout voltage of 3727 V, and a maximum setpoint pickup value of 3806V were determined. These values were used in the analysis to evaluate limiting scenarios for critical voltage and grid separation vulnerability.
The existing Technical Specification setpoint for the degraded voltage relays is 3760V (3740V minimum,3773V maximum). TDR 995, Revision 1, dated 2/21/90, " Voltage Drop Study on Degraded Grid Condition", which is the basis for the existing Technical Specification setpoint, analyzed a minimum voltage of 3741 V on the 4160 V ES buses.
This'was approximately equal to the minimum relay setpoint of 3740 V, cited in the Technical Specifications Bases and reflects a negative 0.53% tolerance applied to the nominal setpoint of 3760V. Calculation C-1101-700-E510-010 analyzed a minimum voltage of 3727 V on the 4160 V ES buses, based on relay dropout tolerance of -0.858%.
This is considered to be a more conservative and appropriate value. The relay pickup setting is not controlled in the Technical Specifications.
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1920-99-20295 Page 3 of 8 l
The minimum "as left" tolerance as specified by the equipment manufacturer of 0.1% has been adopted as recommended in the calculation. In addition, the calibration interval has been changed from the existing refueling interval to annual in accordance with the calculation.
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Notwithstanding these measures, the total negative dropout tolerance of-0.858%
determined in the calculation results in a lower possible minimum voltage on the 4160 V ES buses of 3727 V, versus the 3741 V that was previously analyzed. The efTects of this lower voltage are evaluated below.
1 Minimum Dropout Setting of 3727 V The minimum dropout setpoint of 3727 V was applied in the calculation cases which consider maximum LOCA steady state loading in the short term following the event, to determine the minimum steady state voltage at the terminals of NSR equipment. The acceptance criteria for NSR motors has been established as either providing 90% of motor rated voltage, or alternatively, limiting motor steady state current to its nameplate full load amperage (FLA ) multiplied by its service factor per NRC SER Related to Amendment No.
159 to Facility Operating License No. DPR-50, dated Febmary 25,1991. The minimum voltage for non-motor loads was established by vendor specifications or test results.
Instances were identified wherein certain loads would not receive the desired minimum voltage under worst case conditions. The calculation concluded that each of the loads was acceptable as follows:
- Control Building Emergency Vent Supply Fans AH-E-18A/B These are manually applied loads which may be required for Control Room Habitability following an accident with a radiological release. The motor vendor has provided data l
that supports acceptable operation of these fans under the conditions determined in the I
calculation.
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- Diesel Generator Room Supply Fan (Nor1h) AH-E-29A The motor vendor has provided data that supports acceptable operation of this fan under the conditions determined in the calculation. Also, TDR 900, Revision 1, " Reconciliation of Loss of Ventilation Systems' Analyses and Tests", determined that the maximum allowable Diesel Generator Room temperature of 120 F would not be reached for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following a loss of DG building HVAC, if alternate ventilation is supplied within approximately one hour of the loss of HVAC. Procedure 1104-24M, Revision 13, l
" Diesel Generator Building H & V System", provides for this alternate ventilation.
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1920-99-20295 Page 4 of 8 e Control Building Booster Fans AH-E-95A/B The motor vendor has provided data that supports acceptable operation of these fan under the conditions determined in the calculation.
- Batterv Chargers During the period oflow voltage, DC system loads will be supplied by the batteries which have sutTicient capacity to supply station loads for at least 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> under worst case conditions. Loss of the battery chargers will result in Battery Discharging alarms and 480 ES Bus Undervoltage alarms. These alarms will prompt expeditious operator action to restore the battery chargers.
- Diesel Generator Fuel Pumos DF-P-1 A/C Operation of these motors will be intermittent when the diesel is unloaded as expected in the short term following a LOCA. If the diesel is loaded, adequate voltage will be supplied by the diesel. Lower than rated ambient temperature when the diesels are unloaded will provide additional thermal margin. If the AC motors fail, adequate fuel is supplied by the redundant DC motor.
- Decay Heat River Water Pump Discharge Strainer DR-S-1 A/B These motors experience only a slight voltage deficit (0.5%) which can be eliminated by tripping the extra NR and NS pumps as provided by procedure following a low voltage alarm.
. hiake-un Pumo Gear Oil Pumos hiU-P-4A/B/C The hiU-P-4 pumps provide backup capability for the shaft driven hiU-P-5 pumps.
Therefore operation of the hfU-P-4 pumps is not required for the hiU pumps and the HPI system to perform their ECCS function.
- Nuclear Service River Water Pumo Discharge Strainers The NR-S-1 A/C motors experience only a slight voltage deficit (0.5%) which can be eliminated by tripping the extra NR and NS pumps as provided by procedures following a low voltage alarm. Per vendor data, the NR-S-1B motor may be operated for at least 8 hrs at the maximum current analyzed in the calculation without any loss of motor life.
The worst case voltages discussed above consider steady state post LOCA conditions prior to operator action to improve voltage. In all cases, the NSR loads identified above could tolerate the low voltage conditions postulated either because they were not required to operate, they had sufficient thermal capability beyond the standard criteria set forth in the
1920-99-20295 Page 5 of 8 calculation, or compensatory measures could be taken within a reasonable period of time.
Alarms are present on the switchyard and 480V buses that will alert operators to low voltage. However, the justifications above do not rely on immediate operator action.
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The voltage results from Calculation C-1101-700-E510-010 are similar to the results of TDR 995 Revision 1, which was the basis for Technical Specification Change Request No.
203. TDR 995, Revision 1 justified AH-E-29B on the basis of compensatory operator action. Other loads, such as the Battery Chargers were not evaluited for terminal voltage so nojustification was provided.
TDR 995 Revision 1 analyzed a minirnum switchyard voltage of 229.45 KV with one auxiliary transformer, and a minimum ES Bus voltage of 3741V. Calculation C-1101-700-E510-010 determined that switchyard voltage would have to decline to 225.63 kV in order to result in a voltage of 3727 V of the 4160 V ES Buses. These voltages are considerably below the minimum voltage criteria of 232 kV cited in TMI-l SDD-T1-000, System Design Description For Three Mile Island Nuclear Station Unit No.1, " Division I Plant Level Criteria" for single transformer operation and below the 229.45 KV postulated in TDR 995, Revision 1. In addition, the new voltage criteria takes into account a more rigorous treatment relay uncertainties and tolerances including setting tolerance, drift, instrument transformer accuracy, and other effects that could affect the actual relay operating setpoint, and provides better confidence that the minimum analyzed voltage will not be exceeded.
Therefore, Calculation C-1101-700-E510-010 represents a much more conservative approach for the minimum voltage analysis Calculation C-1101-700-E510-010 also analyzed Long Term Post LOCA cases. These cases explicitly rely on operator actions defined in TMI-I Abnorma! Procedure 1203-41, Revision 20, " Low System (Grid) Voltage", to maintain voltage rather than relying solely on automatic protection of the degraded voltage relays. This approach recognizes that operators must monitor and regulate bus loading during manual operations to assure adequate voltage is available for manually applied and automatic loads. During this operating scenario, operators will have the benefit of alarms, response procedures, and time necessary to maintain voltage at required levels. This operating scenario was not evaluated in TDR 995, Revision 1 and so reliance on operator action in lieu of automatic protection was not explicitly identified in Technical Specification Change Request No. 203.
In response to early NRC concerns regarding degraded voltage, modifications were made to TMI-l that included installation of new first and second level relays and conversion of existing undervoltage relays on the 480V buses to an alarm function. These relays were set to alarm at approximately 92% of 460V, sensed at the unit substation bus, and were cited by the NRC as partialjustification for a second level setpoint that was "less than the usually specified motor low voltage rating of 90%" in their SER associated with Amendment No.
- 70. TMI-l has continued to use these alarms to alert operators oflow voltage conditions.
Alarm Response and Abnormal procedures direct operators to take measures to improve voltage, and ultimately direct them to transfer safety loads to the diesel generators if voltage
1920-99-20295 Enclosure i Page 6 of 8 cannot be restored (Abnormal Procedure 1203-41, " Low System (Grid) Voltage" and Alarm Response Procedure B-2-4, "480V ES Bus UV/OV"). Although the offsite source is considered to be the preferred source, manual transfer to the diesels in case of extreme low voltage is desirable both to assure critical voltage to NSR loads, and to avoid challenges to the automatic transfer scheme, to which the system is vulnerable whenever voltage low enough to trigger low voltage alarms is present.
Manual operator action is not required to provide adequate voltage to important core cooling loads that start automatically at the onset of the accident. Generally, operators are neither expected to start manually operated loads while voltage deficits are present on the ES buses nor are they expected to allow severe voltage deficits to persist without remedial action. Motors running during the early stages of an accident either pass the established voltage criteria or are considered to have suflicient thermal margin to operate until operator action is available to improve voltage. The calculation relies on manual operator action to restore or maintain voltage in the long term post LOCA scenario since the degraded voltage relays may not be adequate to protect the NSR equipment if a degraded grid voltage event occurs while 480 V buses are heavily loaded with automatic and manually applied loads.
And although the manual action in lieu of full automatic protection as implied by the FS AR, introduces the increased possibility of operator error, the possibility and significance of such an error are diminished by the existence of alarms, procedures ar d sufficient reaction time initiate the operator action. Safety is not therefore considered to be degraded significantly by the reliance on this operator action.
IV EFFECTS ON THE ENVIRONMENT No negative environmental impacts which might result from the proposed plant change were identified.
V. CONCLUSION The proposed changes, as confirmed by the voltage regulation study, to the degraded voltage relay setpoint tolerance and calibration interval will reduce the probability that the ES buses will be separated from their offsite power source during low grid voltage conditions. Because of the conservative manner with which the maximum pickup setting was determined, and the measures in place to minimize the probability of experiencing voltages below the setting, it is concluded that the proposed pickup setpoint is consistent with the existing design basis for the availability of the offsite power supply. The proposed change has been found not to be detrimental to the safe operation ofthe plant.
Evaluation confirmed the low probability of two scenarios invohing combinations of either a concurrent LOCA with a single contingency grid event, or a concurrent LOCA with single transformer operation. It was specifically confirmed through calculation that scenarios more limiting than the low probability events analyzed would be ruluired to cause the separation of the ES buses from both offsite sources of power.
1920-99-20295 Page 7 of 8 It can then be concluded that the reduced degraded voltage relay as-left tolerance and calibration interval, in conjunction operator action prompted by existing 480 V ES bus alarms and in accordance with approved procedures, would assure adequate voltage to NSR loads for all required alignments, loading, and grid voltage conditions. This is consistent with the objective of providing a reliable source ofpower for BOP auxiliaries and a continuously available power supply for the ES equipment required by Technical Specification 3.7 bases.
VI. NO SIGNIFICANT HAZARDS CONSIDERATION GPU Nuclear has detemuned that the change proposed to limiting conditions for operation, l
surveillance requiremen:s and design features as addressed in this TSCR involve no significant I
hazards consideration because:
1.
The proposed changes to the degraded voltage relay setpoint tolerance and calibration interval are intended to reduce the total degraded voltage relay setpoint uncertainties.
l These changes will provide greater confidence that minimum voltages necessary to operate NSR equipment are not exceeded. In combination, the proposed changes for degraded voltage relay setpoint tolerance and calibration interval will reduce the probability that the ES buses will be separated from their offsite power source during low grid voltage conditions. This will reduce challenges to the onsite emergency power systems. The proposed changes will enhance the ability of the undervoltage protection scheme to perform in accordance with its intended design, and will improve the ability of the scheme to respond to low voltage conditions caused by malfunction of equipment important to safety.
Therefore, operation of the facility in accordance with the proposed amendment will not involve a significant increase the probability of occurrence or the consequences of l
an accident previously evaluated in the SAR.
2.
The proposed setpoint tolerance and calibration interval changes are consistent with the specifications and intended design of the degraded voltage protection scheme and do not introduce the possibility of any new failure modes to the protection scheme or the electrical distribution system. The proposed changes reduce the probability of insuflicient voltage to NSR loads and reduce the probability of separation of the ES buses from the offsite power source. Therefore, operation of the facility in accordance with the proposed changes do not create a possibility of a new or different type of accident than any previously evaluated in the SAR.
3.
The proposed setpoint tolerance and calibration interval changes are intended to reduce the total degraded voltage relay setpoint uncertainties. The changes will I
provide greater confidence that minimum voltages necessary to operate NSR equipment are not exceeded. The proposed changes will also reduce the probability l
that the ES buses will be separated from their offsite power source during low grid I
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1920-99-20295 Page 8 of 8 voltage conditions. These effects will enhance the objective providing a reliable source of power for BOP auxiliaries and continuously available power supply for the ES equipment, as required by TS 3.7 bases. Therefore, operation of the facility in accordance with the proposed changes would not involve a significant reduction in a margin of safety.
VII. IMPLEMENTATION lt is requested that the amendment authorizing this change become effective 30 days after issuance.