L-99-105, Forwards Response to NRC 990420 RAI Re Previous Responses to GL 95-07, Pressure Locking & Thermal Binding of SR Power-Operated Gate Valves

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Forwards Response to NRC 990420 RAI Re Previous Responses to GL 95-07, Pressure Locking & Thermal Binding of SR Power-Operated Gate Valves
ML20209G182
Person / Time
Site: Beaver Valley
Issue date: 07/08/1999
From: Jain S
DUQUESNE LIGHT CO.
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-95-07, GL-95-7, L-99-105, NUDOCS 9907190070
Download: ML20209G182 (6)


Text

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UE **."U*Svi ion L-99-105

. S. Nuclear Regulatory Commission j

Attention: Document Control Desk j

Washington, DC 20555-0001

Subject:

Beaver Valley Power Station, Unit No.1 and No. 2 BV-1 Docket No. 50-334, License No. DPR-66 BV-2 Docket No. 50-412, License No. NPF-73 Response to Request for Additional Information on Generic Letter 95-07 (dated April 20,1999)

By letters dated October 16, 1995, and February 13, 1996, Duquesne Light Company (DLC) provided 60-day and 180-day responses to Generic Letter (GL) 95-07, " Pressure Locking and Thermal Binding of Safety-Re'ated Power-0perated Gate Valves dated August 17,1995. In addition, DLC provided follow-up responses to two NRC requests for additional information (RAI) by letters dated November 15,1995 and July 24,1996.

By letter dated April 20, 1999, the NRC requested additional information from DLC concerning our previous responses to GL 95-07.

Attached is the BVPS response to the five questions identified in the subject letter.

If there are any questions concerning this matter, please con +act Mr. Mark S. Ackerman, Manager, Safety & Licensing Department at 412-393-5203.

Sincerely,

&&OW Sushil C. Jain 1

f Q( Q Attachment I

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Mr. D. S. Collins, Project Manager Mr. D. M. Kern, Sr. Resident Inspector Mr. R J. Miller, NRC Region I Administrator DiLIVEtING DUAltTY ENEIGV 9907190o7o 99070s a

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Duquesne Light Company Beaver Valley Power Station Units 1 and 2

' Resoonse to Reauest for Additional Information on Generic Letter 95-07 1.

The Nuclear Regulatory Commission (NRC) request for information dated i

June 24,1996, asked if the pressurizer power operated relief valve block valves were susceptible to pressure locking during a steam generator tube-rupture accident. Duquesne Light Company's (DLC's) response dated July 24, 1996, stated that the valves were sized to open with primary pressure on one side and i

ambient pressure on the other side. Your reasoning that the valves will operate during pressure locking conditions because the actuators are sized to operate during differential pressure coralitions does not appear to provide a sound basis to j

preclude pressure locking in these valves. Either clarify your basis or provide j

appro_priate actions to ensure that pressure locking is not a concern for these valves.

I Besponse:

The PORV block valves at both units are adequately sized to operate during potential pressure locking conditions, including a steam generator tube rupture. An engineering assessment has been performed to verify the ability of the valves to open during these conditions using the Westinghouse Owner's Group (WOG) PRESLOK / COMED methodology. The margin results of this assessment are shown as Table No. l.

Table No.1 2

Unit Mark Number Actual Margin' (%)

Design Margin (%)

1 MOV-RC-535 150 41 1

MOV-RC-536 170 42 MOV-RC-537 198 43 2

2RCS-MOV535 162 37 2

2RCS-MOV536 -

198 35 2-2RCS-MOV537 124 33 8 Actual Margin is based on plant test data Design Margin is based on design coefficient of friction and valve factor, and a conservative unseating force

' value 4

i

Attachment Response to Request for Additional Infonnation on Generic Letter 95-07 Page 2 2.

DLC's submittal dated July 24,1996, states that Unit I charging to reactor coolant system hot leg injection valves, MOV-SI-869A/B, are not susceptible to pressure,$.

locking because there are redundant hot leg flow paths, the valves leak and that the " p' valves are not required to be opened until 14.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after initiation of the n

accident. The NRC cons'iders that if the plant's licensing basis requires redundant hot leg flow paths then all the flow paths must be evaluated for pressure locking.

Explain the plant's licensing basis-requirements for valves MOV-SI-869A/B to open. Valve leakage can be used to demonstrate that valves willnot pressure lock u, -

provided that the valves are periodically leak checked. Discuss if valves MOV-SI-8693JB are periodically leak checked. The NRC has accepted that pressure will decay from a valve's bonnet after approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> provided that the temperature of the valve does not increase during the 12-hour period. Describe the -

temperature of valves MO%SI-869A/B during the 14.5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> period after initiation of an accider Either clarify your basis or provide appropriate actions to ensure

~ hat pressure locking is e

> concern for these valves.

J t

Resnonse:

I

':O"6:C. 3 " =..n _u;np:!bb to pressure locking as their susceptible time period for_ the phenomenon 'will have passed prior to their use. Per BVPS-1 UFSAR Section 6.3.3.9, plant licensing basis identifies that 14.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> shall pass after initiation af an accident prior to evaluating the option of stroking these valves during the transfer from RCS Cold Leg re-circulation to simultaneous Cold and 110t Leg re-circulation. This time period will allow valve bonnet pressure to bleed off. DLC design basis calculations identify that a temperature increase will not occur. The temperature seen by MOV-SI-869A & B at the 14.5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> period would be at or less than 150F.

Temperatures at the valves would be decreasing in lieu ofincreasing, negating i

any conditions for thermally induced pressure locking. -

Note that DLC is not crediting specific valve leakage as a mitigating effect for

-valve MOV-SI-869A & B pressure locking as sufficient time will have passed, i

prior to valve usage, to have a pressure locking condition dissipate.

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9 Attachment Response to Request for Additional Information on Generic Letter 95-07 Page 3 3.

DLC's submittal dated February 13,1996, states that an evaluation concluded that Umt I charging to reactor coolant system alternate cold leg injection valve, MOV-SI-836, was not susceptible to pressure locking. Discuss why MOV-SI-836 is not susceptible to pressure locking and include in the discussion the plant's licensing basis requirements for the valve to open and if the valve is periodically leak checked.

Response

The licensing basis at BVPS-1 does not require that MOV-SI-836 be open.

Therefore, the valve is not subject to the requirements of NRC GL 95-07 relative to the pressure locking and thermal binding concerns. No specific time for the valve to open is credited in any of the BVPS-1 UFSAR Chapter 14 DBA analyses. The valve is available for establishing an alternate HHSI flow path and is not required for redundancy per BVPS-1 UFSAR Sections 6.3.1.2 and 6.3.2.1 (redundancy requirements are met by reliance on the LHSI flow paths to the RCS Cold Legs as well as the single active failure proof HHSI path through the BIT).

Note that DLC is not crediting specific valve leakage as a mitigating effect for MOV-SI-836, since the valve is not subject to NRC GL 95-07 concerns.

[

. Attachment Response to Request for Additional Information on Generic Letter 95-07 Page 4 4.

DLC's submittal dated. February 13, 1996, states that valve leakage will prevent Unit 2 residual heat removal system return line to safety injection isolation valves, 2RHS-MOV720A/B from pressure locking.

Valve leakage can be used to demonstrate that valves will not pressure lock provided the valves are periodically leak checked. Discuss when the plant's licensing basis requires the valves to open

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and if the. valves a e periodically leak checked. The NRC has accepted that

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pressure will decay from a valve bonnet after approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> provided that j

the temperature cf the valve does not increase during the 12-hour period. Describe the' temperature of valves 2RHS-MOV720A/B if applicable. Either clarify your basis or provide appropriate actions to ensure that pressure locking is not a concern for these valves.

Response

BVPS Unit 2 UFSAR Appendix 5A provides the design basis for the use of the j

residual heat removal system and states the following:

j i

"While the safe shutdown design basis for BVPS-2 is hot j

standby, the cold shutdown capability of the plant has been 1

evaluated in order to demonstrate how the plant can achieve cold shutdown conditions following a safe shutdown earthquake, assuming loss-of-offs!te power and the most limiting single failure. Under such conditions, the plaat is capable of achieving residual heat removal system [RHS] initiation conditions (approximately 350 F,400 psig) within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />."

Since the RHS is not required to operate prior to the NRC's accepted 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> time period for pressure to decay from the valve bonnet, there is ada ate time available to alleviate any potential hydraulically-induced pressure locking condition for the subject valves (2RHS-MOV720A/B).

l Thermally-induced pressure locking of the subject valves will not be a cancern because the temperature at the valves would be decreasing or stabilized at the time period when valve operation would be considered.

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U Attachment Response to Request for Additional Information on Generic Letter 95-07 Page 5 5.

Explain why Unit 2 recirculation system spray to safety injection valves,2 SIS-MOV8811A/B, safety injection to charging system valves, 2 SIS-MOV863A/B, and safety injection pump recirculation valves, 2 SIS-8890A/B, are not susceptible to pressure locking.

Response

1 The subject valves are capable of operating during potential pressure locking conditions. An engineering assessment has been performed to verify the ability of the valves to open during these conditions using the Westinghouse Owner's Group (WOG) PRESLOK / COMED methodology. The margin results of this assessment are attached as Table No. 2.

DLC intends to either improve the design margin of these valves, as required, to be consistent with the PRESLOK / COMED methodology or perform modifications to ensure long term valve performance. This will be completed by the end of the 2R08 refueling outage. A condition report has been initiated to incorporate this issue into our corrective action program.

Table No. 2 Unit Mark Number Actual Margin'(%)

2 2 SIS-MOV863A 42 2

2 SIS-MOV863B 75 2

2 SIS-MOV8811 A 6

1 2

2 SIS-MOV8811B 3

2 2 SIS-MOV8890A 169 2

2 SIS-M9V8890B 150 t

l 1

I i

1 3 Actual Margin is based on plant test data t