CNL-17-063, Response to Request for Additional Information (RAI) Regarding Application to Modify Technical Specifications Regarding Diesel Generator Steady State Frequency (SQN-TS-14-02)
| ML17299A810 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  (DPR-077, DPR-079) |
| Issue date: | 10/26/2017 |
| From: | James Shea Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CAC MF7762, CAC MF7763, CNL-17-063, SQN-TS-14-02 | |
| Download: ML17299A810 (12) | |
Text
Tennessee Valley Authority, 1101 Market Street, Chattanooga, Tennessee 37402 CNL-17-063 October 26, 2017 10 CFR 50.90 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Sequoyah Nuclear Plant, Units 1 and 2 Renewed Facility Operating License Nos. DPR-77 and DPR-79 NRC Docket Nos. 50-327 and 328
Subject:
Response to Request for Additional Information (RAI) regarding Application to Modify Sequoyah Nuclear Plant, Units 1 and 2 Technical Specifications Regarding Diesel Generator Steady State Frequency (SQN-TS-14-02)
(CAC Nos. MF7762 and MF7763)
References:
- 1. TVA letter to NRC, CNL-16-001, "Sequoyah Nuclear Plant, Units 1 and 2, Application to Modify Sequoyah Nuclear Plant, Units 1 and 2 Technical Specifications Regarding Diesel Generator Steady State Frequency (SQN-TS-14-02)," dated May 26, 2016 (ML16148A175)
- 2. NRC Electronic Mail to TVA, RAI for SQN LAR to Modify Technical Specifications Regarding Diesel Generator Steady State Frequency (CAC Nos. MF7762 and MF7763), dated October 31, 2016 (ML16306A004)
- 3. TVA letter to NRC, CNL-16-178, "Response to Request for Additional Information (RAI) regarding Application to Modify Sequoyah Nuclear Plant, Units 1 and 2 Technical Specifications Regarding Diesel Generator Steady State Frequency (SQN-TS-14-02) (CAC Nos. MF7762 and MF7763)," dated December 23, 2016 (ML16362A209)
- 4. NRC Electronic Mail to TVA, Sequoyah Nuclear Station, Unit 1 & 2 - Request for Additional Information related to LAR for Technical Specification 3.8.1, AC Sources-Operating, dated April 20, 2017 (ML17112A040)
In Reference 1, the Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) to amend the Sequoyah Nuclear Plant (SQN) Units 1 and 2 Technical Specifications (TS) by modifying the acceptance criteria for the diesel generator (DG) steady state frequency range provided in TS Surveillance Requirements (SRs) 3.8.1.2, 3.8.1.7, 3.8.1.9, 3.8.1.11, 3.8.1.12, 3.8.1.15, and 3.8.1.18. In Reference 2, the NRC provided a Request for Additional Information (RAI) related to the proposed change to TS 3.8.1. In Reference 3, TVA provided a response to the RAI. In Reference 4, the NRC provided a second RAI related to the proposed change to TS 3.8.1. The enclosure to this letter provides the response to the RAI included in Reference 4.
As noted in the enclosed RAI response, TVA has revised Sections 3.2.2 and 3.2.3.4 of the
U.S. Nuclear Regulatory Commission CNL-17-063 Page 2 October 26, 2017 enclosure to Reference 1. Section 3.2.3.2 of the enclosure to Reference 1 has also been revised to change + 0.35% to + 0.33% as was noted in Reference 3. The attachment to the enclosure to this letter provides the changes to the Reference 1 enclosure. The attachment to this enclosure supersedes the information provided in Reference 1.
TVA has reviewed the information supporting a finding of no significant hazards consideration and the environmental consideration provided to the NRC in the Reference 1 letter. The supplemental information provided in this submittal does not affect the bases for concluding that the proposed license amendment does not involve a significant hazards consideration. In addition, the supplemental information in this submittal does not affect the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed license amendment.
There are no new regulatory commitments associated with this submittal. If there are any questions or if additional information is needed, please contact Edward D. Schrull at (423) 751-3850.
I declare under penalty of perjury that the foregoing is true and correct. Executed on the 26th day of October 2017.
Respectfully, J. W. Shea Vice President, Nuclear Regulatory Affairs & Support Services
Enclosure:
Response to NRC Request for Additional Information cc: (w/ Enclosure)
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Sequoyah Nuclear Plant NRC SQN Project Manager J. W. Shea Digitally signed by J. W. Shea DN: cn=J. W. Shea, o=Tennessee Valley Authority, ou=Nuclear Licensing, email=jwshea@tva.gov, c=US Date: 2017.10.26 14:41:47 -04'00'
Enclosure CNL-17-063 Page E1 of 4 Response to NRC Request for Additional Information REQUEST FOR ADDITIONAL INFORMATION (RAI)
TENNESSEE VALLE AUTHORITY SEQUOYAH NUCLEAR PLANT UNITS 1 AND 2 LICENSE AMENDMENT REQUEST SQN-TS-14-02 DOCKET NUMBERS 50-327 AND 50-328 (TAC NOS. MF7762 AND MF7763)
NRC RAI 1 On page E8 of 20 of the LAR, the licensee provided an equation to calculate motor speed change as a function of torque. With this equation, the licensee cited a reference to topical report (TR) WCAP-17308, Treatment of Diesel Generator Technical Specification Frequency and Voltage Tolerances. WCAP-17308 is still under NRC staff review and is not an approved TR. Unapproved guidance may be used as the basis for a proposed change, however, the licensee must supply all information necessary (i.e., plant-specific justification and technical basis) to support the change.
Please clarify the licensees reliance on the unapproved TR referenced in the LAR for the equation discussed above, and any other portions of the LAR. Additionally, provide the relevant technical basis, as necessary TVA Response:
Tennessee Valley Authority (TVA) did not use the equation from WCAP-17308 referenced in Section 3.2.2 of the license amendment request (LAR) (Reference 1) to evaluate the effect of frequency variations. The equation from WCAP-17308 on page E8 was provided to show how changes in frequency and voltage can affect motor speed. The requested change only addresses variations in frequency. TVA has revised Section 3.2.2, Comparison of Voltage and Frequency Impact, of the enclosure to Reference 1 to remove reference to the equation from WCAP-17308 (see the attachment to this enclosure). The attachment to this enclosure supersedes the information provided in Reference 1.
NRC RAI-2 On page E12 of 20 of the LAR, the licensee stated that the DG load would increase by 4%
as result of the DG operating at upper end of voltage (7260 V) and frequency (60.2 Hz, proposed change) steady-state ranges. The nominal DG loading values were not provided.
Also, it appears that the 4% increase was calculated in consideration for the motor loads only.
Please provide the following details on DG loading:
a) The change in KW and KVA loading of the DG, showing consideration for the effects on both motor loads and non-motor loads (e.g. heaters) to the total DG load values, b) Maximum postulated loading (KW and KVA) of the DG, if the major pumps are potentially operating at run-out conditions at the onset of an event, c) At nominal voltage and frequency: the maximum postulated, worst-case loading (KW and KVA) for steady-state operation,
Enclosure CNL-17-063 Page E2 of 4 d) At the upper range voltage and frequency: the maximum postulated, worst-case loading (KW and KVA) for steady-state operation, and e) The DG loading compared to the DG rating (minimum margin) for the loading conditions in b), c), and d) above.
TVA Response:
TVA has revised Section 3.2.3.4, Effect on Horsepower Requirements, of the enclosure to Reference 1 to address only frequency variations (see the attachment to this enclosure).
The attachment to this enclosure supersedes the information provided in Reference 1.
As noted in the revised Section 3.2.3.4, TVA has determined that the diesel generator (DG) kilowatt (kW) load would increase by one percent (1%) as a result of operating at the upper end of the proposed frequency range. The results of operating at the upper end of the current technical specification (TS) voltage range are bounded by the results of operating at the upper end of the frequency variations. Therefore, the responses to the information request below are based on a 1% increase in DG kW load values.
Responses to items a) through e) of RAI-2 are provided below.
TVA Response to RAI-2a):
TVA does not separate motor loads from non-motor loads, when calculating the total DG load values. The nominal DG load values provided in the response to RAI-2c) include motor loads and non-motor loads.
Although, non-motor loads are not significantly affected by a frequency increase, the additional DG kW load provided in response to RAI-2d) for the potential variation in frequency allowed by the operating range is conservatively applied to all loads.
TVA Response to RAI-2b):
The nominal DG load values, provided in the response to RAI-2c), assume the worst case mechanical loading, which bounds run-out conditions for major loads, such as emergency core cooling system (ECCS) pumps.
TVA Response RAI-2c):
The maximum postulated, worst-case loading ((kW and kilovolt-ampere (kVA)) for steady-state operation is shown in the following tables for a loss of offsite power (LOOP), a LOOP with a concurrent Phase A safety injection (SIA), and a LOOP with a concurrent Phase B safety injection (SIB).
Enclosure CNL-17-063 Page E3 of 4 Maximum Steady - State Running Load (0 hrs to 2 hrs) kW 1A-A 1B-B 2A-A 2B-B Short-Time Rating Minimum Margin (%)
LOOP 3413.13 3589.95 3594.86 3687.63 4840 23.8 Time
>120 sec
>25 min
>25 min
>120 sec LOOP + SIA 3726.18 3868.80 3901.45 3975.06 4840 17.9 Time
>720 sec
>25 min
>25 min
>720 sec LOOP + SIB 4056.42 4197.20 4272.39 4344.83 4840 10.2 Time
>720 sec
>25 min
>25 min
>720 sec Maximum Steady - State Running Load (0 hrs to 2 hrs) kVA 1A-A 1B-B 2A-A 2B-B Short-Time Rating Minimum Margin (%)
LOOP 3775.66 3977.05 3971.53 4073.29 5500 25.9 Time
>120 sec
>25 min
>25 min
>120 sec LOOP + SIA 4207.34 4368.94 4399.56 4478.99 5500 18.6 Time
>720 sec
>25 min
>25 min
>720 sec LOOP + SIB 4550.78 4708.11 4798.90 4863.29 5500 11.6 Time
>720 sec
>25 min
>25 min
>720 sec Maximum Steady - State Running Load (2 hrs to End) kW 1A-A 1B-B 2A-A 2B-B Continuous Rating Minimum Margin (%)
LOOP 3351.98 3514.35 3576.16 3615.91 4400 17.8 Time End End End End LOOP + SIA 3601.39 3731.80 3748.77 3842.54 4400 12.7 Time End End End End LOOP + SIB 3931.46 4060.05 4119.03 4154.04 4400 5.6 Time End End End End Maximum Steady - State Running Load (2 hrs to End) kVA 1A-A 1B-B 2A-A 2B-B Continuous Rating Minimum Margin (%)
LOOP 3706.21 3894.81 3950.92 3991.01 5000 20.2 Time End End End End LOOP + SIA 4063.12 4213.80 4225.24 4323.80 5000 13.5 Time End End End End LOOP + SIB 4407.27 4553.99 4624.65 4644.92 5000 7.1 Time End End End End
Enclosure CNL-17-063 Page E4 of 4 TVA Response to RAI-2d):
The tables below compare the total steady state kW and kVA load on the worst case DG (i.e., 2B-B) for the worst case scenario (LOOP with SIB), when DG frequency is increased to 60.2 hertz (Hz) from the nominal frequency of 60 Hz and the DG voltage is increased to 7260 volt (V) from the nominal voltage of 6900 V. This condition envelops the other steady state loading scenarios and bounds operating at the upper end of the current TS voltage range.
Maximum Steady - State Running Load (2hrs to End) kW 2B-B Continuous Rating Minimum Margin (%)
Total kW at 60 Hz 4154.04 4400 5.6 Total kW at 60.2 Hz Load Factor = 1.004%
4195.59 4400 4.64 Maximum Steady - State Running Load (2hrs to End) kVA 2B-B Continuous Rating Minimum Margin (%)
Total kVA at 6900 V 4644.92 @ 0.89 power factor 5000 7.1 Total kVA at 7260 V Load Factor = 1.181%
4699.78 @ 0.89 power factor 5000 6.0 TVA Response to RAI-2e):
The minimum margin for the DG loading compared to the DG rating is provided in TVAs response to RAI-2d). The margin provided above bounds operating at the upper end of the proposed frequency range and the upper end of the current TS voltage range.
Reference:
- 1. TVA letter to NRC, CNL-16-001, "Sequoyah Nuclear Plant, Units 1 and 2, Application to Modify Sequoyah Nuclear Plant, Units 1 and 2 Technical Specifications Regarding Diesel Generator Steady State Frequency (SQN-TS-14-02)," dated May 26, 2016 (ML16148A175)
Attachment CNL-17-063 Revised Pages to the Enclosure to TVA letter to NRC, CNL-16-001, "Sequoyah Nuclear Plant, Units 1 and 2, Application to Modify Sequoyah Nuclear Plant, Units 1 and 2 Technical Specifications Regarding Diesel Generator Steady State Frequency (SQN-TS-14-02),"
dated May 26, 2016
ENCLOSURE CNL-16-001 E8 of 20 3.2 Evaluation 3.2.1 Introduction Calculations were conducted to determine the effects of the DG frequency variation between 59.8 Hz and 60.2 Hz on plant equipment fed by the DGs following a loss of offsite power (LOOP) or a loss of coolant accident (LOCA) coincident with a LOOP.
The changes in the DG frequency have the direct effect of changing motor speeds for the motors fed from the generators following a LOOP or a LOOP/LOCA. The changes in motor speeds are addressed in Section 3.2.2 and affect the following components:
x Pumps and Fans (Section 3.2.3) x Air compressors and chillers (Section 3.2.4) x Motor operated valves (MOVs) (Section 3.2.5) x Electrical Equipment (Section 3.2.6)
The changes in these parameters were evaluated to demonstrate that the subject equipment would continue to meet their safety related functions within the analyzed bounds documented in design documents. In addition, the increased horsepower associated with increased frequency was evaluated to ensure that the horsepower increases do not result in exceeding the sustained load ratings for the DGs and the decreased flowrate associated with the revised frequency range was evaluated to ensure pump parameters are adequate. Battery chargers and power transformers do not have motors, but frequency changes were examined to determine if the chargers and transformers would provide acceptable output parameters to continue to meet the specifications and requirements of the downstream components.
The results of these calculations are provided below.
3.2.2 Comparison of Voltage and Frequency Impact DG steady state frequency can vary from 59.8 Hz to 60.2 Hz (+/-0.33% of the rated 60 Hz). Frequencies below 60 Hz decrease motor speed, and frequencies above 60 Hz increase motor speed. Horsepower requirements for a motor increase/decrease by the cube of the speed change. Therefore, increased speed will result in increased horsepower demands and decreased speed will result in decreased horsepower demands on the diesel. Consequently, an under-frequency would not negatively impact diesel generator loading calculations. Not all loads are affected by frequency increase (e.g., battery chargers and transformers); however, it is conservative to assume that they are affected. By applying the upper bound of frequency (60.2 Hz) allowed to the maximum loads calculated for the DG, an additional load can be calculated for the potential variation in frequency allowed by the operating range.
DG steady state voltage can vary from 6800V to 7260V. Voltage variations affect reactive power for motor and static loads, and real power for static loads. By applying the upper bound of voltage (7260V) allowed to the maximum loads
ENCLOSURE CNL-16-001 E9 of 20 calculated for the DG, an additional load can be calculated for the potential variation in voltage allowed.
3.2.3 Effect on Pumps 3.2.3.1 Pump Net Positive Suction Head (NPSH)
The change in the DG frequency was evaluated for the effect on the NPSH available to the following emergency core cooling system (ECCS) pumps. These pumps are fed from the DGs; therefore, they could be affected by the variation in frequency of 59.8 Hz to 60.2 Hz:
x Containment spray (CS) x Safety injection (SI) x Residual heat removal (RHR) x Centrifugal charging (CC)
An evaluation was performed to determine if the NPSH available (NPSHA) exceeds the NPSH required (NPSHR) for the RHR and the CS pumps while taking suction from the containment sump (recirculation mode). The evaluation also determined the NPSH Margin for the CS, SI, RHR, and CC pumps during injection mode operation with suction taken from the refueling water storage tank (RWST). Only the injection mode is presented, as the injection mode has less NPSH margin than the recirculation mode.
3.2.3.1.1 Pump Flow Rates DG frequency affects both the head and flow values based on the pump affinity laws as follows:
Q2 = (N2IN1)*Q1
- where, Q2 = Changed pump flow due to DG frequency variation Q1 = Nominal pump flow N2 = Changed pump speed due to DG frequency variation N1 = Nominal pump speed For the 59.8 Hz frequency, Q2 = (59.8/60.0)*Q1 = 0.997*Q1 For the 60.2 Hz frequency, Q2 = (60.2/60.0)*Q1 = 1.003*Q1 Therefore, a 0.2Hz change in DG frequency will change pump flow by + 0.33%.
ENCLOSURE CNL-16-001 E11 of 20 3.2.3.2 Pump Test Points The DG frequency variation of 59.8 Hz to 60.2 Hz has a negligible effect on plant operations for the above affected pumps based on the revised flow rates in Section 3.2.3.1. The flow change resulting from the DG frequency variation is limited to + 0.350.33%. The pump test acceptance criteria upper limit will be adjusted downward, and the lower limit will be adjusted upward in order to encompass the potential flow variation. The ASME OM Code inservice pump testing acceptance criteria provide assurance that the design basis is met.
3.2.3.3 Effect on Fans DG frequencies above/below 60 Hz directly increase/reduce motor speeds for fans.
Fan speed is directly proportional to fan flow. Therefore, increased/reduced motor speed will result in increased/reduced flows. For the 60.2 Hz DG frequency, fan flows are impacted as follows:
Q2 = (60.2/60.0)*Q1 = 1.0033*Q1 and for the 59.8 Hz DG frequency, fan flows are impacted as follows; Q2 = (59.8/60.0)*Q1 = 0.9967*Q1 where:
Q2 = Changed fan flow due to DG frequency variation Q1 = Nominal fan flow From the above equations, fan flow could vary from nominal to about +0.33%. From the G-Spec (Reference 7), total airflow of a system can vary by +10% at the system fan. Thus, fan flows are within allowed tolerances due to sustained DG frequency variations.
3.2.3.4 Effect on Horsepower Requirements DG steady state frequency can vary from 59.8 Hz to 60.2 Hz (+/-0.33% of the rated 60 Hz). Frequencies below 60 Hz directly decrease motor speed, and frequencies above 60 Hz directly increase motor speed. Horsepower requirements for a motor increase/decrease by the cube of the speed change. Therefore, increased speed will result in increased horsepower demands and decreased speed will result in decreased horsepower demands on the diesel. Consequently, an under-frequency would not negatively affect diesel generator loading. The potential increase in load on the DGs due to operating frequency was evaluated to 60.2 Hz. The highest steady state kW loading was used, which envelops the other steady state loading scenarios.
Motor speed varies directly with the system frequency as shown below:
1/2 = f1/f2 Thus, the speed impact of the frequency variation is (60 + 0.2)/60 or + 0.33%.
ENCLOSURE CNL-16-001 E12 of 20 As noted above, motor horsepower varies directly with the cube of the motor speed:
LoadNew = LoadOld
- Speed3 LoadNew = LoadOld * (1.00333)3 = LoadOld *1.01 Therefore, DG kW load would be increased by 1% if frequency was at the upper limit of 60.2 Hz. Because the DG fuel oil consumption is analyzed for a fully loaded diesel, the frequency variation does not adversely affect the fuel oil analysis.
ENCLOSURE CNL-16-001 E19 of 20
6.0 REFERENCES
1.
TVA Letter to NRC, CNL-14-218, Application to Modify Watts Bar Nuclear Plant, Unit 1 Technical Specification 3.8.1 Regarding Diesel Generator Steady State Frequency (SQN-TS-13-08), dated April 6, 2015 (ML15117A462) 2.
NRC letter to TVA, Watts Bar Nuclear Plant, Unit 1 - Issuance of Amendment Regarding Modification To Technical Specification 3.8.1 Regarding Diesel Generator Steady State Frequency (TAC No. MF6153), dated September 17, 2015 (ML15230A155) 3.
Regulatory Guide 1.9, Revision 0, "Selection of Diesel Generator Set Capacity for Standby Power Supplies" 4.
NRC Administrative Letter 98-10, "Dispositioning of Technical Specifications that are Insufficient to Assure Plant Safety," dated December 29, 1998 5.
Regulatory Guide 1.9, Revision 1, "Selection, Design, and Qualification of Diesel-Generator Units Used as Onsite Electric Power Systems at Nuclear Power Plants" 6.
Not used.
7.
G-Spec G-37 R5, Testing and Balancing of HVAC Systems During Installation, Modification, and Maintenance 8.
Regulatory Guide 1.6, Revision 0, "Independence Between Redundant Standby (Onsite) Power Sources and Between Their Distribution Systems (Safety Guide 6)"
9.
NUREG-1232, Volume 2, Safety Evaluation Report On Tennessee Valley Authority: Sequoyah Nuclear Performance Plan, dated May 1988 10.
NRC Letter, "Beaver Valley 1 and 2 - Amendment for Revised Technical Specification Requirements for Emergency Diesel Generators (TAC Nos. MA4438 and MA4439)," dated February 11, 2000 (ML003684928) 11.
NRC Letter, "Palo Verde Nuclear Generating Station, Units 1, 2, and 3 - Issuance of Amendments on Diesel Generator Steady-State Voltage and Frequency (TAC Nos. MA9214, MA9215, and MA9216)," dated October 4, 2000 (ML003758500) 12.
NRC Letter, Donald C. Cook Nuclear Plant, Units 1 and 2 - Issuance of Amendment to Renewed Facility Operating License Regarding Technical Specification Change Relating to Diesel Generator Steady-State Parameters (TAC Nos. MD8773 and MD8774), dated April 30, 2009 (ML090630245) 13.
NRC Letter, "Crystal River Unit 3 Nuclear Generating Plant - Issuance of Amendment Regarding Request to Revise the Technical Specification Surveillance Requirements for Emergency Diesel Generator Voltage and Frequency Limits (TAC No. ME0107), dated December 10, 2009 (ML092680285)