RC-12-0132, V. C. Summer, Unit 1, South Carolina Electric & Gas (SCE & G) Response to Request for Additional Information License Amendment Request - LAR 10-093912, Technical Specification Change Request for TS 3.5.4, Refueling Water Storage Tank

V. C. Summer, Unit 1, South Carolina Electric & Gas (SCE & G) Response to Request for Additional Information License Amendment Request - LAR 10-093912, Technical Specification Change Request for TS 3.5.4, Refueling Water Storage Tank

ML12258A073
Person / Time
Site:	Summer
Issue date:	09/12/2012
From:	Gatlin T SCANA Corp, South Carolina Electric & Gas Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RC-12-0132
Download: ML12258A073 (9)

Text

Thomas D. Gatlin Vice President,Nuclear Operations 803.345.4342 September 12, 2012 RC-12-0132 A SCANA COMPANY U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555-0001

Subject:

VIRGIL C. SUMMER NUCLEAR STATION (VCSNS) UNIT 1 DOCKET NO. 50-395 OPERATING LICENSE NO. NPF-12 SOUTH CAROLINA ELECTRIC & GAS (SCE&G) RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION LICENSE AMENDMENT REQUEST - LAR 10-03912 TECHNICAL SPECIFICATION CHANGE REQUEST FOR TS 3.5.4, REFUELING WATER STORAGE TANK (RWST)

Reference:

THOMAS D. GATLIN LETTER (RC-12-0075) DATED JUNE 29, 2012, LICENSE AMENDMENT REQUEST - LAR 10-03912 TECHNICAL SPECIFICATION CHANGE REQUEST FOR TS 3.5.4, REFUELING WATER STORAGE TANK (RWST); ADAMS ACCESSION NO. ML121850005 South Carolina Electric & Gas Company (SCE&G) is submitting this response to a request for additional information (RAI) by the Nuclear Regulatory Commission (NRC) regarding License Amendment Request LAR 10-03912, Technical Specification Change Request for TS 3.5.4, Refueling Water Storage Tank (RWST). These requests for additional information were identified during conference calls with the NRC. The NRC RAIs and SCE&G's responses are.

provided in the Attachment.

In addition to submitting the response to this RAI, SCE&G is correcting an erroneous statement in the referenced License Amendment Request. In section 4.0 of the Attachment, SCE&G stated that the boundary valve [XVT6701-SF] was in the locked valve program. In actuality, the valve is caution tagged and will be added to the locked valve program. CR-12-03827 documents this oversight in the station's corrective action program.

There are no regulatory commitments made by this letter.

Virgil C.Summer Station

• Post Office Box 88 *Jenkinsville, SC *29065

• F(803) 345-5209 4o00

Document Control Desk LAR 10-03912 RC-12-0132 Page 2 of 2 If you have any questions about this submittal, please contact Mr. Bruce L. Thompson at (803) 931-5042.

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

Executed on Thomas D. Gatlin JW/TDG/bq

Attachment:

SCE&G's Responses to NRC Questions c: K. B. Marsh S. A. Byrne J. B. Archie N. S. Carns J. H. Hamilton R. J. White W. M. Cherry V. M. McCree R. E. Martin NRC Resident Inspector S. E. Jenkins Paulette Ledbetter K. M. Sutton NSRC RTS (CR-10-03912)

File (813.20)

PRSF (RC-12-0132)

D6cument Control Desk Attachment RC-12-0132 Page 1 of 7 VIRGIL C. SUMMER NUCLEAR STATION (VCSNS) Unit 1 DOCKET NO. 50-395 OPERATING LICENSE NO. NPF-12 ATTACHMENT SCE&G's Responses to NRC Questions

D6cument Control Desk Attachment RC-12-0132 Page 2 of 7

1) The failure of the boundary valve to close could be an issue for LOCAs where the RWST operability is needed for successful mitigation of the accident consequences. For LOCA evaluation under IOCFR50.46, the worst single active failure is assumed.

Failure to isolate the leak path as a single failure has been evaluated. All Emergency Core Cooling System (ECCS) and Reactor Building Spray System pumps and other equipment would function with the single failure of not closing valve XVT06701-SF. The key parameter of concern is the amount of RWST volume transferred into the reactor building, and how that may impact reactor building recirculation sump levels used for Net Positive Suction Head (NPSH) calculations and sump strainer flashing. The net impact is that the reactor building sump level would decrease by about 1 inch. The current NPSH margins are approximately 3 feet and the flashing margin is 7.4 inches. The loss of 1 inch of level does not constitute a limiting single failure.

If the break flow was not isolated through the switchover phase from injection to recirculation, there would be an additional loss of RWST inventory that would shorten available operator action times to complete the switchover. The operator action times take into account single failures. The limiting-single failure is a master relay failure in the automatic switchover logic. This failure results in a RWST inventory diversion of over 20,000 gallons. Considering that operator action times are less than 10 minutes, the RWST inventory loss out of the leak, due to failing to isolate the leak path, would be 2430 gallons. (Note that leak flow rate is based on 18% RWST level that initiates switchover rather than the 94% level). The failure to isolate the leak path is not a limiting single failure for switchover times.

2) Was operator error considered where operator action to close the valve requires more than 21.5 minutes? What are the consequences of 45 minute operator response time?

A specific calculation for a 45 minute operator action time was not calculated. The single failure evaluation for RWST injection described in Question 1 contains a 42 minute break flow time. This resulted in the loss of 1 inch of post-LOCA reactor building recirculation sump level. A 45 minute isolation time (in concert with a different single failure) would result in a little more than a 1 inch level loss, but less than 2 inch level loss, which is still within the margin of both NPSH and flashing calculations.

Dbcument Control Desk Attachment RC-12-0132 Page 3 of 7

3) Given the 21.5 minute operator action time to close the valve, the RWST drains 21.5 minutes earlier. GSI-191 relies on delaying fiber buildup at the core inlet due to lengthy RWST drain times. A 21.5 minute or earlier drain time could result in earlier and faster buildup of fibers at the core inlet and lower spacer grid locations. Fibers at the core inlet delays mixing of boric acid from the core into the lower plenum causing an earlier precipitation time. Has this been evaluated?

The RWST would not drain 21-.5 minutes earlier. During the 21.5 minutes assumed for the operator action to be completed, the RWST is decreasing at a rate of 468 gpm, which results in 10,062 gallons less RWST volume. By maintaining the RWST at 94% level during the alignment, an additional 15,087 gallons of water above the Technical Specification limit is provided to offset the potential loss of 10,062 gallons.

The 94% RWST level during Spent Fuel Pool Purification Loop alignment to the RWST was selected to preserve RWST injection times and volumes. The current minimum RWST injection duration is 24 minutes. With an operator action time of 21.5 minutes, this value is maintained. Similarly, the minimum RWST volume transferred in to the reactor building is maintained. There are no adverse affects on GSI-191 fiber loading or deposition on fuel assemblies due to reduction in RWST injection times.

4) What assurances are there that the proper RWST boron concentrations in the RWST are not altered during this process?

Data collected from 2006 to 2010 was carefully reviewed and no evidence of changes to boron concentration was identified. During that time frame the tank was placed on long term purification for 2 outages and short term purification over 200 times.

5) What are the assumptions and method used to determine the 468 gpm drain flow rate through a double ended guillotine break in the line? Were worst/limiting conditions assumed and what are they?

The elevation head for the flow is based on the RWST elevation at 94% (464.8 ft) minus the elevation of the break location (409 ft) for 55.8 feet. The 3 inch schedule-40 pipe is assumed to have a fully offset double ended guillotine break. The line

D6cument Control Desk Attachment RC-12-0132 Page 4 of 7 taps off the 20 inch RWST outlet. There is assumed to be no outlet flow from the RWST (0 ft of head loss). The piping takeoffs are:

Pipe ID Pipe Area (L/D) f f(L/D)

(in) (ft 2)

Entrance 0.5 37 in. 3.068 0.0513 12.1 0.018 0.22 90 0 LR 14 0.018 0.25 XVT06701 Cv=110 36 in 3.068 0.0513 11.7 0.018 0.21 Exit 1 Total 2.18 Using Darcy's formula:

hL = (Q/Cv) 2 x 2.31 + f(L/D) x v2 /2g 3 / 0.0513 ft2)2 64.4 ft/sec 2 55.8 ft = (Q/1 10)2 x 2.31 + 2.18 x (Q / 60 sec/min 7.48 gal/ft 2

2 55.8 ft = 0.000191 Q2 + 0.0000639 Q = 0.000255 Q Q = 468 gpm Head loss through the valve makes up about 75% of the total head loss. The flow out the break is assumed to remain constant as the RWST level decreases. At the 18% RWST level (switchover from injection to recirculation), the break flow would actually reduce to a flow rate of 243 gpm. The use of a constant 468 gpm flow rate provides conservatism.

6) [This question concerns] substituting the event probability of random failure of the RWST for Human Error Probability (HEP) for closing XVT06701-SF.

It is appropriate to compare, not substitute, the random failure of the RWST as a bounding condition for the HEP for closing and securing XVT06701-SF. The following calculation was used for this conclusion.

Calculation:

Using a factored approach, the event probability of operator failure to close XVT06701-SF (if not currently closed) following a seismic event exceeding OBE can be estimated as follows:

Fraction of the year for XVT06701 -SF not closed: (280+730)/(17*730)=8.14E-02, based on 4 hrs/week for 16 months plus 30 continuous days in a 17 month cycle at power.

Dbcument Control Desk Attachment RC-12-0132 Page 5 of 7 Operational Basis Earthquake (OBE) Frequency: 3.OE-04/yr.

This is determined from FSAR 2.5.2.11 Operating Basis Earthquake estimated maximum horizontal accelerations of 0.10g in rock. This equates to an acceleration of 980 cm/s 2 g*0.1g=98 cm/ S2. From Figure 5-1 in McGuire, R., et al, Probabilistic Seismic Hazard Evaluation for Virgil C. Summer Nuclear Station, Project RP 101-53, Electric Power Research Institute, 1989 the OBE the annual mean probability of exceeding an earthquake with this acceleration is 3.OE-04.

HEP for securing XPP0O14 and closing XVT06701-SF: 9.8 E-04.

Pump breaker fails to open on demand: 1.0 E-03.

Manual Valve Fails to Operate on Demand: 1.OE-04.

Event probability of an operator failure to close XVT06701-SF (if not currently closed) following seismic event exceeding OBE:

8.14E-02*3.0E-04*(9.8E-04+ 1.OE-04+1.OE-03) = 5.1 E-08.

To compare this value, the Current PRA Model @6d, probability, RAW, and CDF contribution values from random failure of the RWST (XTK-25) are given:

Event probability of random failure of XTK-25=1.OE-07. This is on the same order of magnitude as the event probability of an operator failing to secure the pump and close XVT06701-SF. Since the two events would be modeled at the same location(s) in the current model, the impact of the two events is directly proportional and of the same magnitude. The impact on CDF from a random failure of XTK-25 (6.67E-1 1) bounds the impact on CDF from an operator failing to secure the pump and close XVT06701-SF (1.5E-1 1).

7) Description of Valve 6701.

Valve XVT06701-SF is a typical 3 inch manually operated globe valve that is located in the RWST pit. There is ample space available for an operator to manipulate the valve. (See pictures below.)

Dbcument Control Desk Attachment RC-1 2-0132 Page 6 of 7

,Dbcument Control Desk Attachment RC-12-0132 Page 7 of 7

8) What is the distance from valve XVT06701-SF downstream to the non-seismically qualified piping?

Valve XVT06701 is located on a vertical pipe at approximately the 413.5 ft elevation. Code Class 2 support SIH-1469 is located on a horizontal section of pipe at the 402.5 ft elevation. The total pipe length downstream of the valve seismically supported is approximately 15 ft (11 ft vertical + 4 ft horizontal).

9) In SOP-123 Rev 15 the operator is instructed to Cycle XVT06701-SF to ensure operability. The procedure instructs the operator to:

a. Open XVT06701-SF, REFUEL WTR STG TK SF PUR HDR SUP ISOL

b. Close XVT06701-SF, REFUEL WTR STG TK SF PUR HDR SUP ISOL

c. Open XVT06701-SF, REFUEL WTR STG TK SF PUR HDR SUP ISOL Is there any part of the procedure to verify that the valve is not leaking-or in any type of degraded condition after it is first opened and closed before opening it a second time?

A note will be added to SOP-1 23 for step 2.3 that says: if any discrepancies are noted with XVT06701-SF, REFUEL WTR STG TK PUR HDR SUP ISOL, during operation, stop and contact the Control Room immediately for further instructions.

This action has been added to the station's corrective action program.

10) Is XVT06701-SF, RWST Spent Fuel Purification Header Supply Isolation Valve, in the scope of Summer's ASME OM Inservice Testing Program? If so, what are the owner specified test requirements for this valve? If not, what is the justification for exempting it?

XVT06701-SF will be added to the IST program as an active valve that will require a periodic exercise. A determination of whether the valve requires additional testing will be made during our re-evaluation of IN 91-56. These actions have been entered into the station's corrective action program.