ML20236X339

Forwards RAI Re GL 96-06, Assurance of Equipment Operability & Containment Integrity During Design-Basis Accident Conditions. Response Requested by 981031

ML20236X339
Person / Time
Site:	Summer
Issue date:	08/05/1998
From:	Padovan L NRC (Affiliation Not Assigned)
To:	Gabe Taylor SOUTH CAROLINA ELECTRIC & GAS CO.
References
GL-96-06, GL-96-6, TAC-M96872, NUDOCS 9808070306
Download: ML20236X339 (4)

Text

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'4 August 5,1998 Mr. Gary J. Taylor S

Vice President, Nuclear Operations South Carolina Electric & Gas Company Virgil C. Summer Nuclear Station Post Office Box 88 Jenkinsville, South Carolina 29065

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION - GENERIC LETTER 96-06, (TAC NO. M96872)

Dear Mr. Taylor:

Generic Letter (GL) 96-06, " Assurance of Equipment Operability and Containment integrity During Design-Basis Accident Conditions," requested utilities to evaluate cooling water systems that serve containment air coolers to assure that they are not vulnerable to water hammer and two-phase flow conditions. Your January 28,1997, letter provided your assessment of the water hammer and two-phase flow issues for Summer Unit 1. We need additionalinformation as discussed in the enclosure in order to complete our review of your response to GL 96-06. Please provide this information by October 31,1998, in order to support our GL 96-06 review schedule. You can call me at (301) 415-1423 if you have any questions.

Sincerely, Original signed by I

L. Mark Padovan, Project Manager 1 Froject Directorate 111 Division of Reactor Projects - 1/II Office of Nuclear Reactor Regulation Docket No. 50 395

Enclosure:

Request 'or Additionalinformation cc w/ encl: See next page I/

Distribution Docket File J. Zwolinski OGC PUBLIC L. Plisco, Rll ACRS PD ll-1 Reading L. Marsh J. Tatum 'g Ci DOCUMENT NAME: G:\ SUMMER \ SUM 96872.RAI Tu receive e copy of this document. Indicate in the boa: "C" = Copy without attachment / enclosure

• E" = Copy with attachment / enclosure *N* = No coqv .-

0FFICE PDil 1/PM jP lE PDI! 1/LA lF NAME MPadovan M EDunnington /72) l PDIl 1/D /M[C l P.T. Kuo j DATE 08/-4 /98 OP/ V-/98 08/ G 98 OFFICIAL RECORD COPY b / kh .

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9008070306 990005 PDR ADOCK 05000395 P PDR 1

1 ENCLOSURE REQUEST FOR ADDITIONAL INFORMATION t

TO RESOLVE GL 96-06 ISSUES VIRGIL C. SUMMER NUCLEAR STATION Our September 30,1996, Generic Letter (GL) 96-06, " Assurance of Equipment Operability and Containment integrity During Design-Basis Accident Conditions," requested licensees to evaluate cooling water systems that serve containment air coolers to assure that they are not vulnerable to water hammer and two-phase flow conditions. You provided your assessment of the water hammer and two-phase flow issues for Summer Unit 1 in your January 28,1997, letter. You indicated that water hammer (in the form of column separation and rejoining) has been known to occur in the service water system (SWS), which provides cooling water for the reactor building cooling units (RBCUs). You made modifications to the SWS in 1994 to address this problem, and have recently completed analyses in response to GL 96-06. You have concluded that the column separation and rejoining water hammer scenario represents the l bounding case, and modifications you made previously have adequately addressed this issue.

However, your response did not address the two-phase flow concerns. In order to assess your resolution of these issues, we request the information below. You may refer to and supplement, as necessary, information that you submitted previously to provide a complete response to our questions. ,

1. If you used a methodology other than that discussed in NUREG/CR-5220,

• Diagnosis of Condensation-Induced Water hammer," in evaluating water hammer effects, describe this alternate methodology in detail. Also, explain why this methodology is applicable and gives conservative results (typically accomplished through rigorous plant-specific modeling, testing, and analysis).

2. Provide the following information for both the water hammer and two-phase flow analyses:

a. Identify any computer codes that were used in the water hammer and two-phase flow l analyses, and describe the methods used to bench mark the codes for the specific L loading conditions involved (see Standard Review Plan Section 3.9.1).

l b. Describe and justify all assumptions and input parameters (including those used in any l computer codes) such as amplifications due to fluid structure interaction, cushioning, l speed of sound, force reductions, and mesh sizes, 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., fluid structure interaction, flow-induced vibration, erosion).

Confirm that all assumptions and input parameters are consistent with the design and licensing basis of the plant. Please explain and jussy any exceptions.

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c. Provide a detailed description of the *woret case" scenarios for water hammer and two-phase flow, taking into consideration the complete range of event possibilities, system configurations, and parameters, and confirm that all applicable situations have been L considsred. For example, all water hammer types and water slug scenarios should be '

considered, as well as temperatures, pressures, flow rates, load combinations, and potential component failures. Additional considerations for two-phase flow include:

a the effects of void fraction on flow balance and heat transfer; a

the consequences of steam formation, transport, and accumulation; cavitation, resonance, and fatigue effects; and erosion considerations.

It is important for you to realize that in addition to heat transfer considerations, two-

' phase flow also involves structural and system integrity concerns that must be addressed. You might find NUREG/CR-6031, " Cavitation Guide for Control Valves,"

helpful in addressing some aspects of the two-phase flow analyses.

d. Confirm that the analyses included a complete failure modes and effects analysis (FMEA) for all components (including electrical and pneumatic failures) that could i

impact performance of the cooling water system. Also, pleare confirm that the FMEA is documented and available for review, or explain why you did not perform a complete and fully documented FMEA.

e. Explain and justify all uses of " engineering judgment."

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3. Determine the uncertainty in the water hammer and two-phase flow analyses. Also, explain how you determined the uncertainty, and how it was accounted for in the analyses to assure conservative results.

4. Confirm that the water hammer and two-phase flow loading conditions do not exceed any i design specifications or recommended service conditions for the piping system and components, including those stated by equipment vendors. Confirm that the system will I

continue to perform its design-basis functions as assumed in the safety analysis report for the facility, and that the containment isolation valves will remain operable.

5. Discuss specific system operating parameters and other operating restrictions that must be maintained to assure that the water hammer and two-phase flow analyses remain valid (e.g., head tank level, pressures, temperatures; valve operating sequences). Explain why it would not be appropriate to establish Technical Specification requirements to acknowledge the importance of these parameters and operating restrictions. Also, describe and justify reliance on any non-safety-related instrumentation and controls for maintaining these parameters and operating restrictions.

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6. Provide a simplified system diagram showing major components, active components, relative elevations, lengths of piping runs, and the location of any orifices 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 water hammer and two-phase flow issues, including completion schedules, i

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