ML20236Q536

Forwards Request for Addl Info Re GL 96-06, Assurance of Equipment Operability & Containment Integrity During Design- Basis Accident Conditions. Response Requested within 60 Days from Date of Ltr

ML20236Q536
Person / Time
Site:	South Texas
Issue date:	07/14/1998
From:	Alexion T NRC (Affiliation Not Assigned)
To:	Cottle W HOUSTON LIGHTING & POWER CO.
References
GL-96-06, GL-96-6, TAC-M96868, TAC-M96869, NUDOCS 9807200323
Download: ML20236Q536 (5)

Text

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Mr. William T. Cottle July 14, 1998 President and Chief Executive Officer STP Nuclear Operating Company South Texas Project Electric Generating Station P. O. Box 289 Wadsworth, TX 77483

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING GENERIC LETTER (GL) 96-06, " ASSURANCE OF EQUIPMENT OPERABILITY AND l

CONTAINMENT INTEGRITY DURING DESIGN-BASIS ACCIDENT CONDITIONS," SOUTH TEXAS PROJECT, UNITS 1 AND 2 (STP) (TAC NOS.

M96868 AND M96869) l

Dear Mr. Cottle:

The Nuclear Regulatory Commission (NRC) staff is reviewing STP Nuclear Operating Company's (STPNOC's) January 28,1997, response to GL 66-06. STPNOC's response addresses the issues of water hammer and two-phase flow conditions of cooling water systems that serve containment air coolers, and the issue of thermally-induced pressurization of piping runs penetrating the containment. This letter concems the issues of water hammer and two-phase flow. (By letter dated November 11,1997, STPNOC responded to NRC's September 12,1997, I

RAI conceming the latter issue).

i in order for the NRC staff to complete its review of the water hammer and two-phase flow issues, the staff needs the additional information identified in the encicsure. Please respond within 60 days from the date of this letter.

Sincerely, ORIGINAL SIGNED BY:

Thomas W. Alexion, Project Manager

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Project Directorate IV-1 Division of Reactor Projects Ill/IV

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Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499

Enclosure:

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July 14, 1990 Mr. William T. Cottle President and Chief Executive Officer l

STP Nuclear Operating Company South Texas Project Electric Generating Station P. O. Box 289 Wadsworth,TX 77483

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING GENERIC l

LETTER (GL) 96-06,

• ASSURANCE OF EQUIPMENT OPERABILITY AND CONTAINMENT INTEGRITY DURING DESIGN-BASIS ACCIDENT CONDITIONS," SOUTH TEXAS PROJECT, UNITS 1 AND 2 (STP) (TAC NOS.

M96868 AND M96869)

Dear Mr. Cottle:

The Nuclear Regulatory Commission (NRC) staff is reviewing STP Nuclear Operating Company's (STPNOC's) January 28.1997, response to GL 96-06. STPNOC's response addresses the issues of water hammer and two-phase flow conditions of cooling water systems that serve containment air coolers, and the issue of thermally-induced pressurization of piping runs penetrating the containment. This letter concems the issues of water hammer and two-phase flow. (By letter dated November 11,1997, STPNOC responded to NRC's September 12,1997, i

RAI concoming the latterissue),

in order for the NRC staff to complete its review of the water hammer and two-phase flow issues, the staff needs the additional information identified in the enclosure. Please respond within 60 days from the date of this letter.

Sincerely, j

I ra.

Thomas W. Alexion, Proj Manager Project Directorate IV-1 Division of Reactor Projects lil/IV Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499

Enclosure:

RAI cc w/encis: See next page

Mr. William T. Cottle s

STP Nuclear Operating Company South Texas, Units 1 & 2 cc:

Mr. David P. Loveless Jack R. Newman, Esq.

Senior Resident inspector Morgan, Lewis & Bockius U.S. Nuclear Regulatory Commission 1800 M Street, N.W.

P. O. Box 910 Washington, DC 20036-5869 i

Bay City, TX 77414 Mr. Lawrence E. Martin A. Ramirez/C. M. Canady Vice President, Nuc. Assurance & Licensing City of Austin STP Nuclear Operating Company Electric Utility Department P. O. Box 289 721 Barton Springs Road Wadsworth,TX 77483 Austin, TX 78704 Ofiice of the Govemor Mr. M. T. Hardt ATTN: John Howard, Director Mr. W. C. Gunst Environmental and Natural City Public Service Board Resources Policy P. O. Box 1771 P. O. Box 12428

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San Antonio, TX 78296 Austin, TX 78711 l

Mr. G. E. Vaughn/C. A. Johnson Jon C. Wood Central Power and Light Company Matthews & Branscomb P. O. Box 289 One Alamo Center Mail Code: N5012 106 S. St. Mary's Street, Cuite 700 Wadsworth, TX 74483 San Antonio, TX 78205-3692 i

INPO Arthur C. Tate, Director Records Center Division of Compliance & Inspection 700 Galleria Parkway Bureau of Radiation Control Atlanta, GA 30339-3064 Texas Department of Health 1100 West 49th Street Regional Administrator, Region IV Austin, TX 78756 U.S. Nuclear Regulatory Commission i

611 Ryan Plaza Drive, Suite 400 Jim Calloway i

Arlington,TX 76011 Public Utility Commission of Texas Electric Industry Analysis j

D. G. Tees /R. L. Balcom P. O. Box 13326 i

Houston Lighting & Power Co.

Austin, TX.78711-3326 l

P. O. Box 1700 J

Houston, TX 77251 Judge, Matagorda County Matagorda County Courthouse l

1700 Seventh Street Bay City, TX 77414 i

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REQUEST FOR ADDITIONAL INFORMATION (RAI)

+,

GENERIC LETTER (GL) 96-06 SOUTH TEXAS PROJECT (STP). UNITS 1 AND 2 GL 96-06, " Assurance of Equipment Operability and Containment integrity During Design Basis Accident Conditions," dated September 30,1996, included a request for licensees to evaluate cooling water systems that serve containment air coolers to assure they are not vulnerable to waterhammer and two-phase flow conditions. By letter dated January 28,1997, STP Nuclear Operating Company (the licensee) submitted to the Nuclear Regulatory Commission (NRC) its assessment of the waterhammer and two-phase issues for STP.

The licensee has determined that the static pressure in the component cooling water (CCW) system is sufficient to prevent waterhammer, and the effects of two-phase flow through the CCW throttle valves of the containment fan coolers was analyzed and found to be acceptable. In order for the NRC staff to assess the licensee's resolution of these issues, the following additional information is requested:

1. Provide a detailed description of the " worst case" scenarios for waterhammer and two-phase flow, taking into consideration the complete range of event possibilities,.

system configurations, and parameters. For example, all waterhammer types and water slug scenarios should be considered, as well as temperatures, pressures, flow rates, load combinations, and potential component failures. Confirm that all scenarios have been considered. Additional considerations for two-phase flow include:

flow balance and heat transfer effects; the consequences of steam formation, transport, and accumulation; e

cavitation, resonance, and fatigue effects; and e

erosion considerations.

It is important for licensees to realize that in addition to heat transfer considerations, two-phase flow also involves structural and system integrity concems that must be addressed. Licensees may find NUREG/CR-6031, " Cavitation Guide for Control Valves,"

i helpfulin addressing some aspects of the two-phase flow analyses.

2. Discuss specific system operating parameters and other restrictions that must be maintained to assure that the waterhammer and two-phase flow analyses remain valid (e.g., head tank level, pressures, temperatures), and explain why it would not be appropriate to establish Technical Specification requirements to acknowledge the l

importance of these parameters and cperating restrictions. Also, describe and justify reliance on any non-safety related instrumentation and controls for maintaining these parameters and operating restrictions.

3. With regard to the waterhammer concem, describe the minimum margin to boiling that will be maintained for the range of system operating parameters and restrictions that exist.

I ENCLOSURE

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4. Confirm that the waterhammer and two-phase flow analyses included a complete failure modes and effects analysis (FMEA) for all components (including electrical and pneumatic failures) that could impact performance of the cooling water system and confirm that the FMEA is documented and available for review, or explain why a complete and fully documented FMEA was not performed.

5. For the two-phase flow analysis, provide the following information:

a. Identify any computer codes that were used and describe the methods used to bench mark the codes for the specific loading conditions involved (see Standard Review Plan Section 3.9.1).

b. Describe and justify all assumptions and input parameters (including those used in any computer codes), and explain why the values selected give conservative results.

Also, provide justification for omitting any effects that may be relevant to the analysis (e.g., flow induced vibration, erosion).

c. Explain and justify all uses of " engineering judgement."

d. ~ Detarmine the uncertainty in the two-phase flow analysis, explain how t'he uncertainty was determined, and how it was accounted for in the analysis to assure conservative results.

e. Confirm that the two-phase flow loading conditions do not exceed any design l.

specifications or recommended service conditions for the piping system and components, including those stated by equipment vendors; and confirm that the l.

system will continue to perform its design-basis functions as assumed in the safety analysis report for the facility.

6. Provide a simplified diagram of the affected system, showing major' components, active l

components, relative elevations, lengths of piping runs, and the location of any orif'mes and flow restrictions.

7. Describe in detail any plant modifications or procedure changes that have been made or are planned to be made to resolve the waterhammer and two phase flow issues, including completion schedules.

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