ML20274A346
| ML20274A346 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 09/30/2020 |
| From: | Mark D. Sartain Dominion Energy Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 20-315 | |
| Download: ML20274A346 (13) | |
Text
Dominion Energy Nuclear Connecticut, Inc.
5000 Dominion Boulevard, Glen Allen, VA 23060 DominionEnergy.com September 30, 2020 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3 Serial No.
NSS&L/TFO Docket No.
License No.
Dominion Energy 20-315 RO 50-423 NPF-49 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR LICENSE AMENDMENT REQUEST TO REVISE BATTERY SURVEILLANCE REQUIREMENTS By letter dated April 30, 2020, (Agencywide Documents Access and Management System (ADAMS)
Accession No.
Dominion Energy Nuclear Connecticut, Inc. (DENC) submitted a license amendment request (LAR) to the U. S.
Nuclear Regulatory Commission (NRC), to modify Renewed Facility Operating License No. NPF-49 for Millstone Power Station Unit 3 (MPS3). The proposed changes would revise MPS3 Technical Specifications (TS) Surveillance Requirement (SR) 4.8.2.1.b and 4.8.2.1.c, by adding a new acceptance criterion to verify that the total battery connection resistance is within pre-established limits, to ensure that the intended design functions are met.
In an email dated August 18, 2020, the NRC issued a draft request for additional information (RAI) related the proposed changes to the battery surveillance requirements. A conference call was subsequently held with the NRC on August 27, 2020, to provide clarification of the draft RAI. DENC agreed to respond to the RAI by September 30, 2020. In an email dated August 31, 2020, the NRC transmitted the final version of the RAI.
The attachment provides DENC's response to the RAI.
Serial No: 20-315 Docket No. 50-423 Page 2 of 3 Should you have any questions regarding this submittal, please contact Shayan Sinha at (804) 273-4687.
Sincerely, Mark D. Sartain Vice President - Nuclear Engineering & Fleet Support COMMONWEAL TH OF VIRGINIA COUNTY OF HENRICO The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mark D. Sartain, who is Vice President - Nuclear Engineering and Fleet Support of Dominion Energy Nuclear Connecticut, Inc. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of his knowledge and belief.
Acknowledged before me this 3o+h day of 5.e..~.eMAk c, 2020.
My Commission Expires:
12,/3,/zo CRAIG D Notary Pub Commonwealth o My
. Reg.# 7518
Attachment:
Response to Request for Additional Information for License Amendment Request to Revise Battery Surveillance Requirements Commitments made in this letter: None
cc:
U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 R. V. Guzman Senior Project Manager - Millstone Power Station U.S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 08 C2 Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Director, Radiation Division Department of Energy and Environmental Protection 79 Elm Street Hartford, CT 06106-5127 Serial No: 20-315 Docket No. 50-423 Page 3 of 3
ATTACHMENT Serial No.20-315 Docket No. 50-423 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION FOR LICENSE AMENDMENT REQUEST TO REVISE BATTERY SURVEILLANCE REQUIREMENTS DOMINION ENERGY NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNIT 3
Serial No.20-315 Docket No. 50-423 Attachment, Page 1 of 9 By letter dated April 30, 2020, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML20121A217), Dominion Energy Nuclear Connecticut, Inc.
(DENG) submitted a license amendment request (LAR) to the U. S. Nuclear Regulatory Commission (NRC), to modify Renewed Facility Operating License No. NPF-49 for Millstone Power Station Unit 3 (MPS3). The proposed changes would revise MPS3 Technical Specifications (TS) Surveillance Requirement (SR) 4.8.2.1.b and 4.8.2.1.c, by adding a new acceptance criterion to verify that the total battery connection resistance is within pre-established limits, to ensure that the intended design functions are met.
In an email dated August 18, 2020, the NRC issued a draft request for additional information (RAI) related the proposed changes to the battery surveillance requirements.
A conference call was subsequently held with the NRC on August 27, 2020, to provide clarification of the draft RAI. DENG agreed to respond to the RAI by September 30, 2020.
In an email dated August 31, 2020, the NRC transmitted the final version of the RAI. This attachment provides the DENG response to the RAI questions.
Background Information:
The following NRG requirements are applicable to the NRG staff's review of the LAR:
Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix A, General Design Criterion (GOG) 17, "General Design Criteria for Nuclear Power Plants,"
requires, in part, that nuclear power plants have onsite and offsite electric power systems to permit the functioning of structures, systems, and components that are important to safety. The onsite system is required to have sufficient independence, redundancy, and testability to perform its safety function, assuming a single failure.
10 CFR 50, Appendix A, GOC-18, "Inspection and testing of electric power systems," requires that electric power systems that are important to safety must be designed to permit appropriate periodic inspection and testing.
10 CFR 50.36(c)(3), "Technical Specifications," requires that TSs include SRs, which are requirements relating to test, calibration, or inspection to assure that the necessary quality of systems and components is maintained, that facility operation will be within safety limits, and that the limiting conditions for operation will be met.
Additionally, the following guidance document as referenced by the licensee is applicable for conformance to the regulatory requirements:
Institute of Electrical and Electronics Engineers (IEEE) Standard 450-1980 and IEEE Standard 450-1975 "IEEE Recommended Practice for Maintenance, Testing, and Replacement of Large Lead Storage Batteries for Generating Stations and Substations.
The NRG staff also applied the 2002 edition of IEEE Standard 450 as it illustrates methods for measuring battery connection resistance.
Request for Additional Information (RA/)
Serial No.20-315 Docket No. 50-423 Attachment, Page 2 of 9 The licensee proposed adding new acceptance criterion to TS SR 4.8.2.1.b and 4.8.2.1.c to verify that the total battery connection resistance is within pre-established limits, which ensures that the batteries can perform their specified safety functions by maintaining required battery terminal voltage under design-basis load conditions.
Section 3.2.1, "Battery Resistance Evaluation," of the LAR states that Batteries 301A-1 and 3018-1 are model number NGN-27 and Batteries 301A-2 and 3018-2 are model number NGN-11. The LAR further states:
However, because surveillance procedure G SP 760, "Battery Discharge Test" (Reference 6. 7) monitors only the plate-to-post and inter-cell connections and does not include the resistance from the inter-tier and inter-rack cabling (which have a total calculated impedance of 870 micro-ohm), the new calculated bounding acceptance criteria value is 3894 micro-ohm.
To determine th.e acceptability of the proposed TS total battery connection resistance limits, the NRG staff requests the following additional information:
RAl-1 The manufacturer's data sheets indicate that NGN 11 battery cells have two posts per cell and NGN 27 cells have four posts per cell. Therefore, there are differences in the type and number of intercell connections. Section 3.2.1 of the LAR states that resistance sources in the MPS3 battery setup include plate-to-post connections, inter-cell connections, and cabling connections.
The LAR also states that because MPS3 surveillance procedure for the battery discharge test monitors only the plate-to-post and inter-cell connections, the conductor resistance for inter-tier and inter-rack cables is not included in the bounding resistance value of 3894 micro-ohm.
The NRG staff notes that in addition to plate to post intercell connections, there are cabling connections, such as external/terminal cable lug to battery post and inter-tier or inter-rack cable lug to cell post.
These cabling connections are also subjected to resistance changes due to acid related corrosion, loose connection fittings, improper mating surfaces, or material degradation. The LAR does not differentiate between the allowable resistance values for the different types of cell connections for the NGN-11 and NGN-27 cells. Annex F of IEEE Standard 450-2002 provides examples of methods for performing connection resistance measurements for various cell configurations.
Please provide a discussion on any differences between industry accepted guidance (e.g.
Annex F of IEEE 450-2002) for measuring intercell connections for the different types of batteries and methods used at MPS3. In the discussion, confirm that the resistance of the cabling connections (i.e., connections between inter-tier cable lugs, inter-rack cable lugs, terminal cable lugs, multiple posts and battery posts) is included in the bounding resistance value of 3894 micro-ohm.
DENC Response to RAl-1 Serial No.20-315 Docket No. 50-423 Attachment, Page 3 of 9 Figure 1 provides a pictorial layout of the construction of the MPS3 NCN-11 and NCN-27 battery banks, which have 60 cells each.
lntertier Cables MP., Batt<ry 1 Through 6 C<II uyout tShltH 1 Ofl)
Figure 1 lnterrack Cables To provide for the most conservative results, the worst-case battery bank intercell resistance was used in the evaluation of all the battery banks. MPS3 has two NCN-27 batteries (Batteries 1 and 2) and two NCN-11 batteries (Batteries 3 and 4). The NCN-27 batteries have a total of four battery posts (two negative and two positive posts), while the NCN-11 batteries have a total of two posts (one negative and one positive post). A review of the surveillance procedure data shows the NCN-27 batteries produce a higher total intercell resistance due to the additional battery post-to-post connections.
For each of the battery types (NCN-11 and NCN-27), the maximum value of the surveillance procedure's acceptable range for each of the connection resistance types was used as an input to calculate maximum battery impedance. This is conservative since utilizing each actual impedance value would result in lower total calculated impedance. The battery inter-tier and inter-rack cable impedances are not measured in the surveillance procedure but were used as an input to determine overall allowed battery inter-connection impedance.
The inter-tier and inter-rack cables are installed using multiple parallel conductors, and the maximum impedance values are calculated using the equation for parallel cable resistances (considering the cable dimensions and material properties). The maximum impedance values of the inter-tier and inter-rack cabling were identified in the MPS3 calculation for the 125 VDC battery system cable size verification and were used as input. A multiplication factor of 1.25 was added to the calculated values to allow for variation around the actual impedance of the inter-cell, inter-tier, and inter-rack cables.
Serial No.20-315 Docket No. 50-423 Attachment, Page 4 of 9 This information was used in conjunction with the maximum battery duty cycle, bounding battery loading sequence, and a voltage drop analysis to determine the acceptable maximum total impedance for the worst-case battery, which was the NCN-27 battery.
This resulted in a maximum allowed battery impedance of 4764 micro-ohms, which included maximum allowed impedances from plate-to-post at 590 micro-ohms, inter-cell at 3304 micro-ohms, inter-tier cabling at 170 micro-ohms (two segments as shown in Figure 1, each with an impedance of 85 micro-ohm), and inter-rack cabling at 700 micro-ohms (one segment as shown in Figure 1). The surveillance monitored impedance does not include the inter-tier and inter-rack cabling measurements and therefore, the acceptable maximum impedance has been reduced accordingly to 3894 micro-ohms.
However, these inter-tier and inter-rack cablings are the only segments not measured in the surveillance, thus the resistance of the other cabling connections is included in the bounding resistance value of 3894 micro-ohm.
The current licensing basis for MPS3 is committed to following the requirements of Institute of Electrical and Electronics Engineers (IEEE)
Standard 450, "IEEE Recommended Practice for Maintenance, Testing, and Replacement of Large Lead Storage Batteries for Generating Stations and Substations" from 1975 (IEEE Standard 450-1975) and 1980 (IEEE Standard 450-1980) rather than the 2002 version (IEEE Standard 450-2002). However, a review of vendor technical manuals, plant procedures, and measurement techniques was performed and compared to the guidance in IEEE 450-2002 regarding the control of battery intercell connection types and associated acceptance criteria.
Additionally, MPS3 documentation regarding battery assembly, resistance measurement tools, and resistance measurement techniques were reviewed against the acceptance criteria and were found to be in conformance with the IEEE Standard 450-2002 guidance.
Specifically, Annex F of IEEE Standard 450-2002 discusses connection resistance measurement methods.
The methods described in plant procedures align with the methods discussed in Annex F. The lug-to-post measurement (Figure 2) and intercell post-to-post measurement (Figure 3) connection methods from the MPS3 Battery Discharge Test surveillance procedure are provided as follows:
('able Conne<tions 1Lug-to-Post ~IeasuremenO (Sllttdo-tl)
Mul!ipltt::*blinoa da.P,*~nud;q tuc::i::wpl.1.m 1i s
Figure 2 DLRO DunorF~a.r.d~t Usta,;:C-ci:d.p:ratmtl\\.lto
~
Ur;e pMOC at Rp ud.
~* tu otlirupm1:10 Rb f<<u.ot:buf'orwa:-d.&d
~Dw.:t.)rqdt..lf.epe;at ulh.eothup:trt.
lnte1*cell C'om,ectlon, 1Post-to-Post)
(Sheol 1 oil)
T~-'.fou Ctlh ttq,W!"e du.ctotin;
~
confipadan :R.t Four-PouCclh
&quire. Fo~-R.t\\*e:ru:
&x-toris:,;lW!l!~~-tion RaudRb Four-Po,itO!ll DI.RO DI.RO Figure 3 Serial No.20-315 Docket No. 50-423 Attachment, Page 5 of 9 For each tier, the surveillance will measure the resistance starting from the cable lug for the switchgear, inter-tier or inter-rack cable (depending on the tier) to the first cell post, and then from post to post for each of the cells in the tier. The measurement for the tier ends by measuring the resistance from the last cell post to the cable lug for the inter-tier, inter-rack or switchgear cable (depending on the tier). Therefore, the testing method currently utilized at MPS3 for this surveillance aligns with the approach used in the
Serial No.20-315 Docket No. 50-423 Attachment, Page 6 of 9 associated calculations, and adequately considers potential resistance changes in the cabling connections.
Section 3. 1. 2, "Class 1 E Batteries," of the LAR discusses the ampere-hour capacity of the battery systems and the 2-hour sizing criterion.
Section 3.2.1, "Battery Resistance Evaluation," states:
To ensure full functionality of the battery and associated loads with the new total allowable battery inter-cell impedance of 4764 micro-ohm, the most conservative battery draw and associated voltage drop was verified against the load profiles to ensure all battery minimum voltage requirements would be met.
The primary bounding event for batteries is Loss of Onsite Power (LOP), but the calculations supporting the technical evaluation (Reference 6. 6) also reviewed the normal and emergency operation loading as part of the sizing verification.
Please provide a discussion on the calculation which demonstrates that LOP event is the bounding event for the proposed TS total connection resistance of 3700 micro-ohm. In the discussion please provide:
a.) A summary of assumptions, design basis and margins considered for total circuit resistances (battery internal resistance, battery system connection resistance, external conductor and conductor connection resistance, etc.) when evaluating battery load profiles for postulated operational conditions such as LOP. Please include a summary of load profile for other events such as station blackout and LOP coupled with an accident.
b.) Examples of equipment with limiting (minimum) terminal voltage and current conditions required to operate, as the battery terminal voltage approaches 1. 75V per cell at the end of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
DENC Response to RAl-2 a.) A review of the calculation for the Direct Current (DC) System analysis, methodology and scenario development for MPS3 was performed to ensure the bounding battery loading sequence was used in conducting a voltage drop analysis to support the development of the maximum battery impedance. The batteries are required to supply power to required safety related loads for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, and at the end of the 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, have a minimum individual cell voltage of 1.75 voe.
The assumptions and conservatisms contained within the DC System analysis calculation are consistent with IEEE Standard 485, "IEEE Recommended Practice for Sizing Large Lead Storage Batteries for Generating Stations and Substations" from 1978, including circuit resistance effects from battery
Serial No.20-315 Docket No. 50-423 Attachment, Page 7 of 9 internals, connections, and cabling.
Additional examples of conservatisms related to the evaluation of circuit impedance include:
All conductors are modeled using the 90 degrees Celsius cable impedance which is conservative and produces the highest voltage drops.
For constant resistive devices, a conservative assumption is made that the node voltage is at the terminals of the device. This results in larger load currents and a larger corresponding voltage drop than the actual values.
For constant power devices, a conservative assumption is made that the device is operating at its minimum operating voltage. This produces larger voltage drops than the actual values.
For functions that can be performed by redundant devices, each of these devices are considered to be operating for all of the applicable time steps.
This may result in assuming current flow to an alternate redundant device that is not actually operating.
Therefore, the calculated voltage drop will be larger than the actual voltage drop.
All cables were assumed to be coated, which produces more conservative results for voltage drop, except when the cable was considered as part of a short circuit analysis (in which case, lower resistance would be applicable for the condition).
Table 1 shows the battery load step scenario cases for each of the safety-related batteries and indicates which scenario case is bounding. It should be noted that the duration for these cases is 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, except for the Station Blackout (SBO) scenarios, which have a duration of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
Table 1 Battery Load Scenario Cases Case Scenario Battery
- Time Largest Duty Cycle Bound by Steps Current (Amps)
Case#
NCN-27 #1 LOP & Battery 1 and 2 13 440 Composite Charger Failure NCN-27 #2 LOP & EOG 1 and 2 13 440 Composite Failure NCN-27 #3 SBO 1 and 2 13 440 NCN-27 #2 NCN-11 #1 LOP & Battery 3 and 4 4
275 Composite Chan:1er Failure NCN-11 #2 LOP & EOG 3 and 4 4
275 Composite Failure NCN-11 #3 SBO 3 and 4 4
275 NCN-11 #2 Composite Composite 1 - 4 14 440 NA The Composite battery load step scenario envelopes both the worst-case peak amperage draw in each load step and has the longest required duty cycle. This bounds the Loss of Alternating Current Power (LOP) and SBO loading profiles and accounts for design basis equipment loading. The Composite battery load step
Serial No.20-315 Docket No. 50-423 Attachment, Page 8 of 9 scenario was.utilized when evaluating the acceptability of the new bounding intercell connection impedance.
b.) A battery terminal voltage of 1. 75 VOC per cell equates to a battery voltage of 105 VOC for the MPS3 batteries with 60 cell batteries, which bounds the minimum required duty cycle voltages for the components powered by the batteries. Except for motors, the minimum required voltage for all panels and devices is assumed to be 100 VOC plus one volt if it is not available from the manufacturer. The minimum required voltage for motors is assumeo to be 90 VOC plus one volt. One volt is added to the minimum required voltage to account for panel internal wiring and jumpers. This is based on purchase specification requirements in anticipation of the acceptable end of duty cycle battery terminal voltage.
The previously calculated worst case voltages for the limiting components were decreased by a factor of 2.162 VOC. This factor accounts for a maximum voltage drop attributed to the battery intercell connection, based on the most conservative current draw of 440 amps over a resistance of 4764 micro-ohms. It also accounts for a worst-case decrease in the voltage margin value of 0.072 VOC, which corresponds to the impedance of the battery cell cart if a single failed battery cell is jumpered out of service.
Table 2 includes other examples of limiting calculated minimum voltages for additional components during the 2-hour battery duty cycle, and the minimum required voltages.
Table 2: Component Node Voltage Examples Device Node Path Equivalent Circuit Rcable Calculated Required Voltage Voltage Impedance Amp (0)
Voltage at Voltage (VDC)
Drop (0)
Draw Relay Coil (VDC)
(VDC)
(Amps)
(VDC) 52X-3HVK*CHL 1A 112.97 20.01 20.76 6.02 3.68 95.96 91 (Breaker Reclosing Relay for AC Unit &
Computer Room) 52X-3SWP*P1 B 108.70 17.70 20.76 6.02 3.38 93.46 91 (Breaker Reclosing Relay for "B" Service Water Pump)
X-3HVU-FN1B 105.95 4.62 (Breaker Reclosing Relay for Containment Structure Air Circulating Fan)
X-3HVU-FN2B 107.13 4.47 (Breaker Reclosing Relay for Containment Structure Air Circulating Fan) 20.76 6.02 0.91 20.76 6.02 0.87 Serial No.20-315 Docket No. 50-423 Attachment, Page 9 of 9 101.50 101 102.82 101 As shown in Table 2, the limiting calculated minimum voltages meet their minimum required voltages with margin throughout the 2-hour battery duty cycle.