NG-09-0054, Response to Request for Additional Information Pertaining to a License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value
| ML090620585 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 02/27/2009 |
| From: | Richard Anderson Duane Arnold |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NG-09-0054 | |
| Download: ML090620585 (18) | |
Text
FPL Energy Duane Arnold, LLC 3277 DAEC Road Palo, Iowa 52324 FPL Energy.
Duane Arnold Energy Center February 27, 2009 NG-09-0054 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Duane Arnold Energy Center Docket 50-331 License No. DPR-49 Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value
References:
- 1. Letter, R. Anderson (FPL Energy Duane Arnold) to Document Control Desk (USNRC), "Technical Specification Change Request (TSCR-106): 4160V Emergency Bus Undervoltage (Degraded Voltage) Maximum Allowable Value," dated May 30, 2008, NG 0366 (ML081630205)
- 2. Letter, K. Feintuch (USNRC) to R. Anderson (FPL Energy Duane Arnold), "Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value (TAC No. MD8950)," dated January 12, 2009 (ML090090416)
In Reference 1, FPL Energy Duane Arnold, LLC requested an amendment to the Duane Arnold Energy Center (DAEC) Technical Specifications (TS) revising the TS maximum allowable value for the 4160 volt Emergency Bus Undervoltage (Degraded Voltage) relays.
The Staff held a telephone conference with FPL Energy Duane Arnold on January 9, 2009 to discuss a request for additional information regarding Reference 1. The Staff's request for additional information was formally transmitted to FPL Energy Duane Arnold by letter dated January 12, 2009, Reference 2. The response to this request is provided in the enclosure to this letter.
This letter makes no new commitments or changes to any existing commitments.
If you have any questions or require additional information, please contact Mr. Steve A Catron at (319) 851-7234.
/~/Q pg~
Document Control Desk NG-09-0054 Page 2 I declare under penalty of perjury that the foregoing is true and correct.
Executed on February 27, 2009.
Richard L. Anderson Vice President, Duane Arnold Energy Center FPL Energy Duane Arnold, LLC Enclosure cc: Administrator, Region III, USNRC Project Manager, DAEC, USNRC Resident Inspector, DAEC, USNRC D. McGhee (State of Iowa)
Enclosure Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value 15 Pages Follow
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value NRC Question 1:
Provide excerpts from documents which explain that the emergency bus voltage will recover to 95.5% (upper analytical value of degraded voltage relay) following the worst-case design-basis accident. Confirm whether the worst-case scenario is when the maximum safety-related loads are fed from the standby transformer, whose tap setting was changed to get the transformer secondary voltage by approximately 2.8% (according to the Licensee Event Report No. 2007-10-00 dated January 29, 2008).
FPL Energy Duane Arnold Response:
The current calculation of record relevant to this response is CAL-E08-004, Main AC Electrical Distribution Analysis, Posted Change 1 to Revision 0, 2/24/09.
The DAEC electrical design bases calculations for offsite power sources are comprised of three analytical scenarios. Graphs illustrating the results of the ETAP analysis for each of the three analytical scenarios have been provided. The ETAP analysis looks at separate cases where each division is supplying the majority of the electrical power. The Train A graph represents a scenario where the A division, powered from the 1A3 emergency bus, is the most heavily loaded. The Train B graph represents the 1A4 emergency bus as most heavily loaded.
Scenario I - LOCA with 4 kV Emergency Buses Powered From the Standby Transformer This scenario concludes that the minimum steady state 4 kV emergency bus voltage during a LOCA is 96.88% which is above the required degraded voltage reset value of 94.64%. These results are representative of the post tap change configuration for the Standby Transformer.
With a margin of 2.24% it is the least limiting of the scenarios.
ETAP results for the first 30 seconds of this model are illustrated in the following Figures:
- Figure 1: PSB-1, Standby Transformer, Train A, Initial Condition: Mode 1
- .Figure 2: PSB-1, Standby Transformer, Train B, Initial Condition: Mode 1 Page 1 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Figure 1 PSB-1, Standby Transformer, Train A, Initial Condition: Mode I 102 100 98 0) 96 I F -- 1A3 0
94
-- 1A4 Max Reset
Max Dropout 92 ý..r............
90 88 0 0 5 10 15 20 2 30 Tim\(Seconds)
Both Core Spray'Pumps Start 1st 2 RHP' Pumps Start 2 nd 2 RHR Pumps Start Page 2 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Figure 2 Both Core Spray Pumps Start 1st 2 RHR Pumps Start 2 nd 2 RHR Pumps Start Page 3 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Scenario 2 - LOCA During Transition with 4 kV Emergency Buses Powered From the Startup Transformer This scenario simulates a LOCA during plant startup or shutdown with both essential and non-essential loads being supplied by the Startup transformer. Non-essential bus load is limited to 22 MWe which is consistent with current operating procedure limits. In this scenario, the degraded voltage relay is actuated upon start of the Core Spray Pumps, as shown in Figures 3 and 4. 4 kV emergency bus voltage then recovers to 94.73%, resetting the degraded voltage relay. 4 kV emergency bus voltage does not drop below the maximum relay drop out again during the scenario. Therefore, although steady state 4 kV emergency bus voltage is below the required degraded voltage reset value, Figures 3 and 4 show that the 4 kV emergency buses will recover within the relay time delay and so they will remain connected to offsite power throughout this scenario. This represents our most limiting scenario.
ETAP results for the first 30 seconds of this model are illustrated in the following Figures:
- Figure 3: PSB-1, Train A, Initial Condition: Startup
- Figure 4: PSB-1, Train B, Initial Condition: Startup Page 4 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Figure 3 Page 5 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Figure 4 PSB-1, Train B, Initial Condition: Startup 98 97 96 94r ___1A 95 1A3 a 94 .. .1A4
- Max Reset 93
....... Max Dropout 92 91 90 89
/5 0 10 15 20 2 30 Time econds)
Both Core Spray Pumps Start 1 st 2 RHR Pumps Start 2 nd 2 RHiR Pumps Start Page 6 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Scenario 3 - LOCA at Full Power with 4 kV Emergency Buses Powered From the Startup Transformer This scenario concludes that the minimum steady state 4 kV emergency bus voltage during a LOCA is 92.88%. This minimum steady state voltage is reached after all safety-related loads are sequenced onto the 4 kV emergency buses and all balance of plant loads are block transferred from the Unit Auxiliary transformer to the Startup transformer at approximately T=1 minute. This transfer occurs coincident with the reverse power trip of the main generator. It is important to note that in this model, the degraded voltage relay actuation setpoint is never reached. Therefore, the available margin is determined as the minimum steady state emergency bus voltage of 92.88% minus the worst case degraded voltage relay trip value of 91.88% for 1.0% of margin.
ETAP results for the first 30 seconds of this model are illustrated in the following Figures:
- Figure 5: PSB-1, Train A, Initial Condition: Mode 1
- Figure 6: PSB-1, Train B, Initial Condition: Mode 1 Page 7 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Figure 5 PSB-1, Train A, Initial Condition: Mode I 100 99 98 97
-1A3 a' 96 ____1A4 95 Max Reset Max Dropout 94 ---------------
93 92 91 0 5 10 15 20 7ýý---------
2.5 \ 30 Time Seconds)
Both Core Spray Pumps Start 1st 2 RHR Pumps Start 2 nd 2 RHR Pumps Start Page 8 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Figure 6 PSB-1, Train B, Initial Condition: Mode I 100 99 98 97 at
.5 96 rz --
1A3 1A4
-.... Max Reset 95 94 -------I-------- \---------ý,\------------------ ---------Max Dropout 93 92 ...1..
91 0 5 10 15 20 25\ 3'0 1 Time Seconds)
Both Core Spray Pumps Start 1st 2 RHR Pumps Start 2 nd2 RHR Pumps Start Page 9 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value In response to NRC Question 1 concerning the 95.5% upper analytical value of the degraded voltage relay, FPL Energy Duane Arnold's analysis is based solely on the degraded voltage relay lower analytical limit. In December 2007, via modification ECP-1846 and revision 4 of CAL-E95-006, "4.16 kV Essential Bus Degraded Voltage Setpoint Calculation," the degraded voltage relay setpoints were modified. Calculation CAL-E95-006, revision 4, was included as an attachment to FPL Energy Duane Arnold's July 17, 2008, "Response To Request For Supplemental Information," (ML082050395). By eliminating excess margin, utilizing higher accuracy calibration test equipment, and adjusting the instrument drift based on actual calibration data, the nominal setpoint, and perhaps equally important, the relay reset value have been reduced. The table below illustrates the degraded voltage relay setpoints before and after the modification.
Parameter Before After Allowable As-Found 108.0 to 111.4 volts 108.0 to 109.2 volts Range (90.9 to 93.7%) (90.87 to 91.88%)
Nominal Setpoint 109.5 volts 108.5 to 108.7 volts (92.1%) (91.29% to 91.45%)
Max Reset Value 114.7 volts 112.5 volts (1.03 x Max Allowable As (96.5%) (94.64%)
Found Trip Value) L I Page 10 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value NRC Question 2:
Provide the minimum switchyard voltage value and its basis assumed in the above requested document.
FPL Energy Duane Arnold Response:
The results of all three analytical models discussed in the response to the previous question are based on the 161 kV switchyard voltage being at the minimum value of 99.2%.
From CAL-E08-004 Section 5.1.1.3, The minimum 161kV switchyard voltage used to determine operabilityof the switchyard is 99.2%. The switchyard is targetedfor 99.2% or greaterand if the real time projected post trip voltage drops below this value, the plant will declare this offsite source inoperable.
A 99.2% minimum grid voltage alarm limit has been established via the grid operating agreement with our electric grid operator.1 In June of 2008, eastern Iowa experienced historic flooding. As a result of flood related damage to local generating stations and substations, the electric grid operator requested that the minimum grid voltage alarm be temporarily lowered. In response to this request, FPL Energy Duane Arnold revisited the three analytical models described in response to NRC Question 1 above. FPL Energy Duane Arnold has determined that a minimum grid voltage of 98.5% will support the emergency bus loading requirements for models 1 and 3. Emergency bus loading requirements for model 2, however, can only be satisfied if loads are reduced. Consequently, in response to the temporary distribution system conditions, FPL Energy Duane Arnold has agreed to the reduced limit of 98.5%
and has developed procedural guidance to be implemented if grid voltage is predicted to be below 99.2%, but above 98.5%. Predicted grid voltage below 98.5% requires the offsite sources to be declared inoperable in accordance with Generic Letter 2006-02.
Page 11 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Additional Information As discussed with the Staff during the January 9, 2009 teleconference, the following graphs are being transmitted to illustrate actual plant data from reactor SCRAMs from 100% power on three different occasions. These graphs each show:
- date of the SCRAM,
- initiation of reactor SCRAM, indicated by the lowering of Generator MWe,
- initiation of generator reverse power trip/transfer of BOP loads from the Unit Auxiliary transformer to the Startup transformer, indicated by the breaker transfer and supported by the lowering of generator RPMs (i.e. the generator is no longer connected to the grid),
and
- elapsed time from SCRAM to reverse power trip.
While CAL-E08-004 conservatively assumes 1 minute, the critical factor is that the load transfer occurs after ECCS pump load sequencing and recovery to steady state voltage (not before T =
- 20 seconds).
Page 12 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Graph I 0.
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- PI D2 P1 Data from 1/5/2000. Turbine trip to bus transfer approximately 78 seconds.
Page 13 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value Graph 2 0L
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I I 0 PI Data from 8/12/2001. Turbine trip to bus transfer approximately 98 seconds.
Page 14 of 15
Response to Request for Additional Information Pertaining To A License Amendment Request to Revise the 4160 Volt Bus Undervoltage (Degraded Voltage) Maximum Allowed Value 3
.9-0 0
PI Data from 10/17/2001. Turbine trip to bus transfer approximately 97 seconds.
Page 15 of 15