A97023, Provides Response to NRC RAI for Addl Info Re Mod Necessary to Address Issues Identified in GL 96-06, Assurance of Equipment Operability & Containment Integrity During Design- Basis Accident Conditions

Provides Response to NRC RAI for Addl Info Re Mod Necessary to Address Issues Identified in GL 96-06, Assurance of Equipment Operability & Containment Integrity During Design- Basis Accident Conditions

ML20203F617
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	12/09/1997
From:	Brons J COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-96-06, GL-96-6, ZRA97023, NUDOCS 9712170422
Download: ML20203F617 (6)

Text

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/ son il ukm 2v Irl H r ' 6t, Jim 4 ZRA97023 December 9,1997 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention

Document Control Desk

Subject:

Zion Nuclear Power Station, Units 1 and 2 Response to Request for Additional Information Regarding Generic Letter 96-06, " Assurance of Equipment Operability and Containment Intetfity During Design 13 asis Accident Conditions" b'RC_QMkcGOLiQ-L91and.10dQ4

References:

1) Letter from C. Shirati, NRC, to 1. Johnson, Commonwealth Edison, dated July 7,1997, Request for Additional Informa6on, Generic Letter 96 06, " Assurance of Equipment Operability and Containment Integrity During Design-Ilasis Accident Conditions" Zion Nuclear Power Station, Unit 2.

2) Letter from J.13 llosmer, Comed to U S. Nuclear Regulatory Commission, dated January 28,1997, Commonwealth Edison Company (Comed) Response to Nuclear Ragulatory Commission (NRC) Generic Letter (GL) 96 06, " Assurance of Equipment Opsbility and Containment integrity During Design-11 asis Accident Conditinns," dated September 30,1996

3) Letter from J, B. Ilormer, Comed to U S. Nuclear Regulatory Commissio ., dated May 2,1997, Commonwealth Edison Compar:y (Comed) Response to Nuclear Regulatory Commission (NRC) Generic Letter (GL) 96-06, " Assurance of Equipment Operability and Containment Integrity During Design Basis Accident Conditions." dated September 30,1996.

I This letter provides Comed's response to an NRC Request for Additional Information (Reference 1) regarding modifications recessary to address the issues identified in GL 96-06.

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Zila 97023 Page 2 cf 5 llackground Generic Letter 96 06 " Assurance ofliquipment Operability and Containment integrity During Design llasis Accident Conditions," dated September 30,1996, requested that licensees evaluate potential vulnerabilities associated with water hammer, two phase flow, and thermally induced overpressuriration in fluid systems, and take corrective actions as appropriate. Coml!d's response to GL 96-06, dated January 28,1997, (Reference 2) stated that its evaluations were not complete and that the details of the final resolution would be provided prior to hiay 31,1997.

In a letter dated hiny 2,1997 (Reference 3), Comed identified two options under consideration fbr resolving the water hammer issue, provided infonnation indicating that the two phase flow issue was not applicable to Zion, and described the planned actions to address the thennally induced overpressurization issue. The hiay 2,1997, letter also indicated that modifications to resolve the water hammer issue and modifications to resolve the overpressure issue ihr Unit 2 would be completed during the next refueling outage, Z2R15.

Subsequently, the NRC requested in Reference I that " Comed justify its decision to restart and operate Unit 2 lbr an entire fuel cycle without knowing the extent of the modifications necessary to address the waterhammer issue and its plans for corrective action impleraentation of the GL 96-06 issues if the restart of Unit 2 is delayed."

On November 13,1997, GL 96 06 Supplement I was issued. This supplement informs addressees about ongoing elTorts and new developments associated with GL 96 06 and provides additional guidance fbr completing corrective actions. The GL Supplement indicates,"It is the staft's current position that addressees can use the ash 1E Code, Section lit Appendix l' criteria for interim operability detenninations fbr degraded and nonconfonning piping and pipe supports until permanent actions have been identified and approved by the NRC (as applicable) Ibr resolving the GL 96-06 issues."

Response

in response to the NRC concerns, Comed is providing clarification regarding the efforts that have been undertaken to resolve the water hammer issue, providing justification for restart of Unit 2 prior to implementing the final resolution for the water hammer and overpressurization issues, and providing a description of its plans for implementing the resolutions if Unit 2 restart is delayed.

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'lhe " initial waterhammer assessment and operability determination"(water hammer assessment) referred to in the second paragraph ofiteference I was completed, as described in iteference 3. using a conservative approach to develop water hammer loads. The water hammer assessment was not a " preliminary analysis" as indicated in iteference 1. The water hammer assessment determined that the pipe stresses would be within the ASME Class 2/3 limits for faulted conditions (which is more restrictive than GL 91 1UASME Section 111 Appendix F criteria), and that the majority of the stresses would be less than the design allowable stresses. The water hammer assessment also concluded that pipe support stresses would be within the limits specified in ASME Section til Appendix F, with the majority of the stresses being less than the design allowable stresses.

'Ihe " additional evaluation" referred to in the second paragraph ofiteference I was conducted to provide a basis for selecting which resolution option would be pursued.

The evaluation consisted of a Sargent & l. undy study which more accurately determined the loads that might occur. The Sargent & Lundy study, which began in early June 1997, was completed in August. The results of this study indicated that the loads would be less than 50% of the loads predicted in Iteference 3. Therefore, in addition to providing a basis for final option selection, the results confirm the conservative nature of the water hammer assessment described in iteference 3.

Ilased on the predicted load reduction and the engineering and material costs associated with the slow refill system option identified in iteference 3 Comed plans to complete detailed load and stress calculations using the Sargent & Lundy study methods and implement the option of modifying pipe supports as necessary to ensure the affected piping and support stresses meet the design allowable stressess. Ilased on preliminary results of the detailed load and stress calculations, Comed projects that very few modifications will be necessary to accommodate the additional loadin;t from the system retill, with the most likely scenario being that no modifications will be necessary.

Comed believes restart of Unit 2 and operation for one cycle prior to completion of the Unit 2 modifications is justified for the following reasons:

. The piping configuration was conservatively evaluated (in the water hammer assessment) and it was determined that the predicted pipe stresses and the resultant loads and stresses fbr the supports, meet ASME Section 111 Appendix F criteria.

• The conservatism of the water hammer assessment has been confirmed by the Sargent & Lundy study and the preliminary results of the detailed load and stress calculations. The preliminary results indicate that few if any modifications will be necessary.

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• 1he following unlikely conditions must be present simultaneously for the RCFC supply / return service water piping to experience the increased loading described in GL 96 06:

Loss of OfL:ite Power (LOOP),

Loss of Coolant Accident (LOCA) or Main Steam Line Ilreak (MSLII),

and Opposite unit service water pumps unavailable or fail to start.

'Ihese simultaneous conditions are necessary to create the increased loading for the following reasons. Since the service water system is normally cross connected between units, a LOOP on both units must occur to deenergize all service water pumps and reduce the water pressure in the RCFC lines. This reduces the temperature at which boiling would occur. A LOCA or MSLI) must occur to add heat to the senice water and cause boiling and void formation in the RCFC lines.

Finally, no opposite (non LOCA) unit service water pump must be available. The system design is such that the service water pumps will restart sooner following a 1.OOP than they would following a LOCA. The non LOCA unit service water pump would start in approximately 17 seconds based on the Illackout sequence timer, while the LOCA unit service water pump would stan aller approximately 30 to 36 seconds based on the Safety injection sequence timer. The more rapid pump restart would repressurize the service water in the RCFC lines prior to significant void formation.

The complex modeling of the service water system and the associated caiculations to detennine the required support modifications are planned for completion in the first quarter of 1998. Issuance of modifications, if required,is expected in May 1998. This date is aller the currently scheduled Unit 2 restart. The modifications to the Unit 2 supports will be no later than Z2Rl5, which was the commitment made in Reference 3.

Thermal Overpressuritation Issue Comed is currently engaged in a project to design and install relief devices to resolve the issue of thermally induced overpressurization ofliquid filled piping systems which penetrate containment. Comed considers restart of Unit 2 and operation for a cycle prior to completion of the Unit 2 overpressurization modifications to bejustified. As described in Reference 3, operability of the nine affected piping systems was demonstrated by showing that the pennanent strain developed would be on the order of 2% to 3%, but no higher than 6% in the worst case. These strains are well below the n,cumerw u w w w ua u

e l ZRA97023 PageSof5 ultimate strain for the material. None of the systems subject to overpressure perform an active post accident safety related function. The associated containment ir.olation valves have been evaluated and are considered operable and capable of perfonning their safety function (providing containment isolation and maintaining structural integrity).

The relief device sires and setpoints have been determined and equipment delivery is expected in the second quarter of 1998, which is aller the currently scheduled Unit 2 restart. The associated modifications are complex in that some of the modifications involve routing of piping to tanks located inside containment, which would require the plant to be in a shutdown condition. Therefore, Comed plans to install the Unit 2 relief devices during Z2R15, as stated in Reference 3. In addition, Comed plans to evaluate the information provided in GL 96-06, Supplement I to determine if other technically feasible and cost beneficial alternatives are available for each of the 9 affected piping systems. If the evaluation of Gl 96 06, Supplement I leads to a change in the resolution of the Thennal Overpressurization issue, Comed will pmvide a supplement to the Gl,96-06 response.

Delay in Unit 2 Restart if Unit 2 restart is delayed beyond the point at which the modifications are available, Comed will consider installation of the required modifications during the current outage, provided the installation does not increase the restart delay.

Attached to this letter is a listing of the commitments made by Comed in this submittal.

Please direct any questions you may have concerning this submittal to this ollice.

Respectfully, r -

hn C. Ilrons (yk S te Vice President Z on Nuclear Station Attachment ec: NRC Regional Administrator - Rill Zion Station Project Manager NRR Senior Resident inspector Zion Station Office of Nuclear 17acility Safety -IDNS IDNS Resident inspector L Wgnmptgen-Itr\%-0MWA. tral doc

ATTACllMENT Page1of1 List of Commitments identified in Zila 97023 The following table identifies those actions committed to by Comed in this document.

Any other actions discussed is this submittal represent intended or planned actions by Comed. They are described to the NitC for the NitC's information and are not regulatory commitments. Please notify Mr. Itobert Godley, Zion Station llegulatory Assurance Manager, of any questions regarding this document or any associated regulatory commitments.

Commitment Committed Date or Outage The modifications to the Unit 2 service water supports associated with No later than resolution of the water hammer issue will be made no later than Z2it!$ Z2it15 which was the commitment made in Iteference 3.

If Unit 2 restart is delayed beyond the point at which the modifications March 1.1998 are available, Comed will consider installation of the required modifications during the current outage, provided the installation does not increase the restart delay.

If the evaluation of Gl. 96-06, Supplement I leads to a change in the N/A resolution of the Thermal Overpressurization issue, Comed will provide a supplement to the GL 96-06 response.

All other commitments remain as stated in Iteference 3. N/A i

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