ML19071A357

Request for License Amendment to Virgil C. Summer Nuclear Station Technical Specification 3.8.2., D.C. Sources - Operating, Surveillance Requirements 4.8.2.1.b.2 and 4.8.2.1.c.3 - Request for Additional Information

ML19071A357
Person / Time
Site:	Summer
Issue date:	03/11/2019
From:	Lippard G South Carolina Electric & Gas Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
19-013
Download: ML19071A357 (10)

Text

< scE&G A SCANA COMPANY March11,2019 U.S. Nuclear Regulatory Commission Serial No.19-013 Attention: Document Control Desk VCS LIC/TS/Rev 0 Washington, DC 20555-0001 Docket No. 50-395 License No. NPF-12 SOUTH CAROLINA ELECTRIC & GAS COMPANY VIRGIL C. SUMMER NUCLEAR STATION (VCSNS) UNIT 1 LICENSE AMENDMENT REQUEST - LAR-10-02395 REQUEST FOR LICENSE AMENDMENT TO VIRGIL C. SUMMER NUCLEAR STATION TECHNICAL SPECIFICATION 3.8.2, "D.C. SOURCES- OPERATING," SURVEILLANCE REQUIREMENTS 4.8.2.1.b.2 AND 4.8.2.1.c.3 REQUEST FOR ADDITIONAL INFORMATION By letter dated September 27, 2018 (Agencywide Documents Access and Management Systems (ADAMS) Accession Number ML18270A360), South Carolina Gas & Electric Company (SCE&G) requested changes to Virgil C. Summer Nuclear Station, Unit 1 Technical Specifications (TS). The proposed amendment would correct a non-conservative TS 3/4.8.2, "D.C. Sources Operating," by revising the inter-cell resistance value listed in Surveillance Requirements 4.8.2.1 .b.2 and 4.8.2.1.c.3.

By email dated January 9, 2019, the Nuclear Regulatory Commission (NRC) staff provided a request for additional information (RAJ) to complete their review. Virgil C. Summer Nuclear Station's response to the RAI is provided in the attachment to this letter.

Should you have any questions or require additional information, please contact Mr. Michael S.

Moore at (803) 345-4752.

I declare under penalty of perjury that the foregoing is true and correct.

Executed on Vice President, Nuclear Operations V.C. Summer Nuclear Station V. C. Summer Nuclear Station* P. 0. Box 88

• Jenkinsville, South Carolina* 29065

• F(803) 941-9776

• www.sceg.com

Serial No.19-013 Docket No. 50-395 Page 2 of 2 Commitments contained in this letter: None Attachment V. C. Summer Response to NRC Request for Additional Information cc: (Without Attachment Unless Indicated)

C. Haney S. A. Williams (w/Attachment)

NRC Resident Inspector G. J. Lindamood S. E. Jenkins (w/Attachment)

Serial No.19-013 Response to RAI for LAR-10-02395 Page 1 of 1 be: S. M. Zarandi - VCS R. R. Haselden - VCS J. H. Hamilton - VCS C. D. Sly - IN2SE M. S. Moore - VCS J. A Langan - MPS D.R. Taylor- NAPS B. A Garber - SPS James Roth - IN2SE Vicki Hull - lN2SE (w/Attachment)

W. S. Blair - RS P. Ledbetter- VCS RTS (CR-10-02395)

File (813.20)

PRSF (SN 19-013)

Concurrences:

See Correspondence Routing and Approval CHOP Sheet Verification of Accuracy Hardcopy of SN 19-013 Technical Verification Team Package Action Plan : CR-10-02395 None; Response to RAI Changes to the UFSAR, USAR, QA Topical Report, ISFSI FSAR, DSAR or PSDAR:

None

Serial No.19-013 Response to RAI for LAR-10-02395 VIRGIL C. SUMMER NUCLEAR STATION (VCSNS) UNIT 1 DOCKET NO. 50-395 OPERATING LICENSE NO. NPF-12 ATTACHMENT V. C. SUMMER NUCLEAR STATION RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION

Serial No.19-013 Attachment Page 1 of 6 By letter dated September 27, 2018 (Agencywide Documents Access and Management System Accession No. ML18270A360) South Carolina Electric & Gas Company (SCE&G) requested changes to the Technical Specifications (TSs) for the Virgil C. Summer Nuclear Plant, Unit 1. The proposed amendment would correct a non-conservative TS 3/4.8.2, "D.C. Sources Operating" by revising the inter-cell resistance value listed in Surveillance Requirements 4.8.2.1.b.2 and 4.8.2.1.c.3.

The U.S. Nuclear Regulatory Commission (NRC) staff has reviewed the submittal and determined that additional information is needed to complete its review.

Regulatory Requirement 10 CFR 50.36(c)(3), "Technical Specifications," include SRs [Surveillance Requirements],

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. The SR 4.8.2.1 in the licensee amendment request (LAR) is related to the requirements 10 CFR 50.36(c)(3).

Request for Additional Information (RAI) No. 1 In the LAR Enclosure, on Page 6, the licensee stated that the general approach to calculate a maximum allowable battery connection resistance for VCSNS Class 1E station batteries XBA-1A-ED (Train A) and XBA-18-ED (Train B) is to determine the minimum amount of available voltage margin from battery discharge (voltage drop) calculation DC08320-010, and then use some of that available voltage margin to accommodate battery connection resistance. A primary goal for this approach was to not impact the minimum allowable battery terminal voltage of 108-volt DC used to size the VCS Class 1E station batteries in calculation DC08320-005.

It is not clear to the NRC staff how the minimum amount of available voltage margin was calculated in the above mentioned calculation DC08320-010. Please provide a summary of the calculation DC08320-010, including the data used and assumptions made in the calculation.

SCE&G Response:

LAR-10-02395, Enclosure Table 3-3, Maximum Allowable Battery Connection Resistance Above Intrinsic summarizes the most limiting components and the available voltage margin at the terminals of these components. This table states that Train A inverter XIT5901 has a margin of 1.0 Vdc and Train 8 inverter XIT5904 has a margin of 0.6 Vdc.

Serial No.19-013 Attachment Page 2 of 6 LAR T a bl e 3 -3Max,mum

. . tance Ab ave In tnns,c Allowa ble B atterv Connec t"JOn R es1s . .

Component Max Max Allowable Limiting Time Limiting Voltage Allowable Train Resistance Above of Duty Cycle Component Margin Measured Intrinsic (µQ)

(Vdc) Resistance XIT5901 A 0-1 minute 1.0 2430 3030 (Inverter No. 1) 239-240 XIT5904 B 0.6 2290 2890 minute (Inverter No. 4)

A discussion on the methodology used to conclude these are the most limiting components is provided later in response to RAI 2.

There are three design calculations that together define the design basis for these voltage margin values.

1. DC08320-005, ESF 1 A & 1 B Capacity. This calculation determines the battery size necessary for LOOP/LOCA loads during a 4-hour Station Blackout (SBO) duty cycle.

The batteries are sized so the battery terminal voltage with 58 of 60 cells connected is 108 Vdc at the end of the duty cycle . The batteries are sized per Standard IEEE 485-1983. The sizing analysis includes scenarios for 58, 59, and all 60 cells available.

2. DC08320-010, Class 1E 125 Volt DC System Voltages and Voltage Drop. This calculation develops detailed resistance diagrams and performs a voltage drop analysis to determine if sufficient voltage exists at the terminals of Train A and B components at the time they are required to operate during design basis events (LOOP/LOCA/SBO).

3. DC08320-020, V. C. Summer Class 1E 125 Vdc System Maximum Allowable Battery Connection Resistance. This calculation determines the maximum battery connection resistance that ensures the most limiting loads have sufficient voltage to perform their design basis function. This calculation uses design inputs from calculations DC08320-005 and DC08320-010.

With 58 of 60 cells connected , DC08320-010 makes the following conclusions at the end of the 4-hour duty cycle that are relevant to this LAR.

1. Train A inverter XIT5901 will have 105.64 Vdc at its terminals .

2. Train B inverter XIT5904 will have 104.62 Vdc at its terminals.

The limiting battery discharge analysis calculated in DC08320-010 is a 58-cell analysis (i.e., two cells out of service). Based on a review of the 58-cell analysis output reports from calculation DC08320-010, the minimum terminal voltages calculated during the discharge are 108.6 Vdc for Train A and 107 .5 Vdc for Train B. The limiting duty cycle time for Train A inverter XIT5901 is the first minute. The limiting duty cycle time for Train B inverter XIT5904 is the last minute (239-240 minutes).

Calculation DC08320-010 also tabulates the minimum voltage for components required to operate during design basis events. This information is used by calculation DC08320-020 to find the most limiting components and determine the maximum allowable battery connection resistance. From calculation DC08320-010, the inverters require 104 Vdc minimum to perform their Class 1 E function, which is to power the Class 1E 120 Vac vital busses.

Serial No.19-013 Attachment Page 3 of 6 Calculation DC08320-020 applies the voltage drop analysis of calculation DC08320-010 to tabulate the analyzed components, the available terminal voltage and the minimum terminal voltage to determine the unadjusted available margin for each component. From this analysis, the most limiting component on Train A is determined to be inverter XIT5901 with 1.64 Vdc unadjusted margin and inverter XIT5904 on Train B with 0.6 Vdc unadjusted margin. Before the final margin can be determined, a voltage adjustment is necessary to account for the calculated verses the designed (108 Vdc) end of duty cycle battery terminal voltage.

For the Train B battery, the existing battery discharge analysis shows that with a battery terminal voltage of 107 .5 Vdc during the limiting time in the duty cycle, all loads have adequate voltage. This is conservative for battery sizing and component operating margin because the batteries are sized to remain above 108 Vdc using the sizing methodology of Standard IEEE 485-1983. For the Train A battery, the existing battery discharge analysis determines a final terminal voltage of 108.6 Vdc. Therefore, to ensure the methodology in calculation DC08320-020 is conservative, all Train A minimum available voltages are reduced by 0.6 Vdc before determining the impact of connection resistance on the available voltage margin.

Applying this 0.6 Vdc adjustment to Train A inverter XIT5901, the final voltage available at the

=

terminals is 105.64 - 0.6 105 Vdc. The margin for this component is 105 Vdc - 104 Vdc 1.0 =

Vdc. Since no adjustment for Train B is needed, the margin for inverter XIT5904 is 104.62 Vdc -

104 Vdc = 0.6 Vdc. The final margin values (1.0 Vdc and 0.6 Vdc) are tabulated in Enclosure Table 3-3 of LAR-10-02395 and Table 1-1 of DC08320-020. A summary of this margin analysis is provided in Table 1 of this RAI response.

RAI T a bl e 1 - S ummaryo f th e VoIta ge M argm. D eveopmen I t tior Inve rt ers XIT5901 I 5904 Parameter XIT5901 XIT5904 Source Terminal VoltaQe (Vdc) 105.64 104.62 DC08320-010 Calculated Battery Discharge 0.6 0 DC08320-020 Adjustment (Vdc)

Adjusted Terminal Voltage (Vdc) 105 104.62 DC08320-020 Minimum Re9.uired VoltaQe (Vdc) 104.0 104.0 DC08320-010

= , 'FinarMargin-(Vdc) 1.0 0.6 DC08320-020

Serial No.19-013 Attachment Page 4 of 6 RAI No. 2 In the LAR Enclosure, on Page 8, the licensee stated that it performed calculation DC08320-020 to determine combination of allowable individual connection type resistances (as provided in the Table 3-4 in the LAR) that would not exceed the maximum allowable measured connection resistance of 2890 µO.

Please provide a summary of calculation DC08320-020, including the data used and assumptions made in the calculation to determine the individual limiting inter-cell, jumper, and terminal plate resistances (after determining the maximum allowable total battery resistance).

SCE&G Response:

The analysis develops a design basis for the maximum allowable total connection resistance of both trains of the Class 1E 125 Vdc batteries. Maintaining the total battery connection resistance at or below a maximum allowable value ensures all DC loads necessary to mitigate a design basis event will have adequate voltage to perform their design basis function.

The general approach taken by the analysis is to determine the minimum available voltage margin from the DC voltage drop analysis and then use some of that available voltage margin to account for a maximum measured connection resistance. When accounting for this maximum measured connection resistance, the goals of this approach (1) ensures the existing end-of-duty-cycle battery terminal voltage (108 Vdc) remains acceptable, (2) ensures the present size of the VCS Class 1E station batteries continues to be acceptable, (3) ensures the most limiting DC load(s) has sufficient voltage to perform the required design basis function(s), and (4) the correction factors included in the battery sizing calculation to account for battery aging, temperature, 10% design margin, and battery capacity margin remain available for the VCS Class 1E 125 Vdc system even with the maximum battery connection resistance included.

The steps taken to implement this approach are:

1. Identify which loads/circuits are required to mitigate a LOOP/LOCA and/or an SBO.

2. Determine the minimum required voltage for each required load/circuit.

3. Determine the existing minimum available voltage for each required load/circuit.

4. Calculate the voltage margin between the existing minimum available voltage and the minimum required voltage for each required load/circuit.

5. Determine the overall minimum voltage margin for each train.

6. Calculate the amount of equivalent battery connection resistance the voltage margin allows given the bounding discharge rate of the battery for that train at the time the circuit/load is required to operate.

The key technical basis behind this approach is understanding that most loads in the DC system are constant impedance loads with no known constant current loads and the only notable constant power loads are the 120 Vac Vital Inverters. Consequently, the system-wide impact to the constant impedance loads has the largest overall effect on battery performance.

The configuration of each train of VCS Class 1E station battery is 56 intercell connections, 3 jumpers and 2 terminal plate connectors. This includes 59 cell-to-cell connections (for a 60-cell

Serial No.19-013 Attachment Page 5 of 6 battery) plus the positive and negative connections of the battery terminals (61 total connections).

The maximum allowable total resistance is comprised of two elements - battery connection resistance and intrinsic connection resistance . The battery connection resistance is the value that is measured in the plant and is in addition to the intrinsic connection resistance . The intrinsic connection res istance is defined as the res istance present when the battery vendor performed discharge testing of the batteries to develop the battery curves used in the battery sizing and battery discharge analysis. The intrinsic connection resistance was assumed to be an average of 1OµQ per connection , which is conservatively low, for a total intrinsic connection resistance of 600µ0 for each 60-cell battery.

Summary of Conclusions The DC system voltage drop analysis concluded that a battery terminal voltage of 108 Vdc at the end of the four-hour battery duty cycle results in 104 Vdc at the terminals of the Class 1 E Vital Inverters. For both trains, ensuring 104 Vdc terminal voltage to the inverters is the limiting constraint on the maximum allowable connection res istance . As shown in LAR-10-02395 ,

Enclosure Table 3-3 and discussed above, Train A (Inverter No. 1) is limited in the first few seconds during a LOOP/LOCA while emergency onsite power sources are starting. Train B (Inverter No. 4) is the most limiting in the last minute of the four-hour Station Blackout event.

For both battery trains, the 120 Vac Vital Inverters were found to be the most limiting overall component at both the first and last minute of the four-hour battery duty cycle. The most limiting connection resistance of the two trains was found to be Train B (Inverter No. 4) . Using the most limiting connection resistance (2290 µQ) in conjunction with an assumed 600 µQ of intrinsic connection resistance, the maximum allowable measured connection resistance is 2290 + 600 =

2890 µQ and bounds both battery trains.

LAR T a bl e 3 -3Max,mum

. Allowa ble Ba tterv Connec fJOn R es,s. t ance Ab ave In tnns,c Component Max Max Allowable Limiting Time Limiting Voltage Allowable Train Resistance Above of Duty Cycle Component Margin Measured Intrinsic (µQ)

(Vdc) Resistance XIT5901 A 0-1 minute 1.0 2430 3030 (Inverter No. 1) 239-240 XIT5904 B 0.6 2290 2890*

minute (Inverter No. 4)

• most limiting LAR-10-02395, Enclosure Table 3-4 , Maximum Measured Individual Battery Connection Resistances, is intended to illustrate one possible combination of allowable individual connection resistances (intercell, jumper, terminal plate) that will not exceed the measured maximum allowable connection resistance of 2890 µO per battery train. The average resistance values in the third column of the table were selected based on resistance test data and the administrative limits previously analyzed. The purpose of the res istance values was to provide an example average resistance for each component (intercell, jumper, term inal plate) that is reasonable and above the measured res istances and administrative limits while resulting in a cumulative resistance of less 2890 µO . Resistance combinations other than these provided in

Serial No.19-013 Attachment Page 6 of 6 this table should be expected and are acceptable provided these actual measured resistance combinations do not exceed a maximum allowable value of 2890 µ.O.

LAR Ta bl e 3-4 M ax,mum

. M easure d In d.1v1'dua I B a ttery Connect'JOn R es,s

. tances Individual Total Connection Connection Max Connection Number of Average Maximum Measured Type Connections Measured Measured Resistance Resistance Resistance (µO)

(µ0) (µ0) lntercell 56 45 2520 Jumper 3 100 300 2890 Terminal Plate 2 35 70 These results are applicable to 60-cell, 59-cell, and 58-cell battery operations. Minimum voltage margins (and therefore maximum allowable connection resistances) were calculated assuming 58-cell operations and therefore additional margin is present when operating in either 59-cell or 60-cell configuration.