LR-N980325, Forwards Response to 980430 RAI Re GL 96-06 Re Licensee Determination If Containment Air Cooler Cooling Water Systems Are Susceptible to Waterhammer of two-phase Flow Conditions During Postulated Accident Conditions

Forwards Response to 980430 RAI Re GL 96-06 Re Licensee Determination If Containment Air Cooler Cooling Water Systems Are Susceptible to Waterhammer of two-phase Flow Conditions During Postulated Accident Conditions

ML20236M434
Person / Time
Site:	Hope Creek
Issue date:	07/07/1998
From:	Eric Simpson Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-96-06, GL-96-6, LR-N980325, NUDOCS 9807140077
Download: ML20236M434 (8)

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l Pubic Servce Electre and Gas

. Company E. C. simpson Public Service Electric and Gas Company PO, Box 236. Hancocks Bndge, NJ 08038 609-339-1700 Spor Vee President . tJoclear Eng'nwfng JUL 0 71998 LR-N980325 L

United States Nuclear Regulatory Commission

, Document Control Desk l

Washington, DC 20555 1

, Gentlemen:

REPLY TO REQUEST FOR ADDITIONAL INFORMATION NRC GENERIC LETTER 96-06 HOPE CREEK GENERATING STATION FACILITY OPERATING LICENSE NPF-57 DOCKET NO. 354 Generic Letter (GL) 96-06 was issued by the NRC on September 30,1996. It included l

a request for licensees to determine if containment air cooler cooling water systems are susceptible to waterhammer or two-phase flow conditions during postulated accident

conditions. Public Service Electric and Gas Co. (PSE&G) provided its response by letter dated January 27,1997.

By letter dated April 30,1998, the NRC requested additional information in order for the l NRC staff to complete its review of PSE&G's response.

The PSE&G response to the request for additiona! information is contained in the Attachments to this letter. If you have any questions or comments on this transmittal,

, please contact Paul Duke at (609) 339-1466.

I j_ Sincerely, c 9

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Attachments (2) i 9007140077 990707 l PDR ADOCK 05000354 ;

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Document Control Desk LR-N980325 JUL 07 7999 C Mr. H. Miller, Administrator - Region i U. S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Mr. R. Ennis, Licensing Project Manager- Hope Creek U. S. Nuclear Regulatory Commission One White Flint North

' 11555 Rockville Pike Mail Stop 14E21 Rockville, MD 20852 Mr. S. Pindale (X24)

USNRC Senior Resident inspector- HC Mr. K. Tosch, Manager IV Bureau of Nuclear Engineering P. O. Box 415 Trenton, NJ 08025 l

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ATTACHMENT 1 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 96-06 HOPE CREEK GENERATING STATION DOCKET NO. 50-354

Background

Generic Letter (GL) 96-06 was issued by the NRC on September 30,1996. It included a request for licensees to determine if containment air cooler cooling water systems are susceptible to waterhammer or two-phase flow conditions during postulated accident conditions. PSE&G provided its response by letter dated January 27,1997.

PSE&G reviewed the design basis and procedural guidance for use of the non-safety related drywell coolers in post-LOCA and post Main Steam Line Break (MSLB) scenarios to evaluate susceptibility to water hammer and two-phase flow conditions.

Since the drywell coolers are not credited in the Hope Creek accident analysis to mitigate the consequences of a LOCA or MSLB, the heat removal assumptions for design basis accident scenarios would not be adversely impacted by any potential for two-phase flow in the drywell coolers.

1 To evaluate susceptibility to water hammer, the procedures controlling drywell cooler operation during post accident scenarios were reviewed. Based upon this review, it was determined that drywell cooler isolation interlocks were overridden in accordance with Emergency Operating Procedure HC.OP-EO.ZZ-0102A(B). This Emergency Operating Procedure (EOP) directed the operator to place all drywell coolers in service, if available, by overriding the containment isolation interlocks when high drywell temperatures exist in post accident scenarios. PSE&G determined that this action could

, result in a water hammer when attempting to place the drywell coolers in service under certain post accident drywell conditions.

' Although the exact magnitude of the water hammer loads was not determined, PSE&G

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concluded that the system containment penetrations were not designed for potential water hammer loads, and as a result, containment integrity could be challenged during i these post accident scenarios when the isolation interlocks are overridden. As an - 1 L interim compensatory action, administrative controls were implemented to prohibit use  !

L of the isolation override feature for the drywell cooler water supply penetrations. )

PSE&G planned to take corrective action by either revising the Hope Creek EOPs to i address overriding of the containment isolation interlocks of the chilled water system; or  !

reanalyzing or modifying the affected containment penetrations to accommodate the l water hammer loads.  !

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.. Atta:hm:nt 1 LR-N980325 NRC Question 1 Implementing measures to assure that waterhammer will not occur, such as prohibiting l

post accident operation of the affected system, is an acceptable approach for addressing the waterhammer concern. However, all scenarios must be considered to assure that the vulnerability to water hammer has been eliminated. Confirm that all scenarios have been considered, including those where the affected containment penetrations are not isolated (if this is a possibility), such that the measures that have been established are adequate to prevent occurrence of a water hammer during (and l following) all postulated accident scenarios.

1 PSE&G Response 1 To eliminate susceptibility to waterhammer, Containment Control Emergency Operating Procedure, Drywell Temperature Leg, HC.OP-EO.ZZ-0102A(B) has been revised to remove overriding the containment isolation interlocks for the drywell cooler chilled water system containment isolation valves. Entry into the EOP's are symptom based and not scenario dependent. The drywell cooler chilled water containment isolation valves will remain closed after closing automatically in response to a containment isolation signal. This method of resolution is acceptable since no credit is taken for operation of the drywell coolers post accident. There is no existing procedure which directs the operator to override the containment isolation signal to open the chilled water supply and return valves to restore drywell cooling. No single failure can prevent isolation of the affected piping. For those accident scenarios (UFSAR Table 15.0-2) where there is no containment isolation signal generated (high drywell pressure or low reactor level), the temperature inside drywell is expected to remain at or near normal j operating temperature preventing the potential for two phase flow and waterhammer.

Thus, PSE&G concludes that the measures established are adequate to prevent occurrence of a waterhammer or two-phase flow conditions during and following all postulated accident scenarios.

NRC Question 2 If a methodology other than that discussed in NUREG/CR-5220, " Diagnosis of Condensation-induced Waterhammer," was used in evaluating the effects of waterhammer, describe this attemate methodology in detail. Also, explain why this methodology is applicable and gives conservative results for the Hope Creek plant (typically accomplished through rigorous plant specific modeling, testing and analysis).

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., Attachm:nt 1 LR-N980325 PSE&G Response 2 As noted in the Request for Additional Information, this question is only applicable to those event scenarios where the occurrence of waterhammer has not been eliminated.

Since measures are in place to assure waterhamrner will not occur, this question is not applicable to Hope Creek.

NRC Question 3 For both the waterhammer and the two-phase flow analyses, provide the following information:

a. Identify any computer codes that were used in the waterhammer and two phase flow analyses and describe the methods used to benchmark 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) such as amplifications due to fluid structure interaction, cushioning, 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). fj

c. Provide a detailed description of " worst case" scenarios for water hammer and two phase flow, taking into consideration the complete range of event possibilities, j system configurations, and parameters. For example, all waterhammer types and i water slug scenarios should be considered, as well as temperatures, pressures, flow rates, load combinations and potential component failures. Additional examples include: '

• the consequences of steam formation, transport, and accumulation:

e cavitation, resonance and fatigue effects; and e erosion considerations.

1 Licensees may find NUREG/CR-6031, " Cavitation Guide for Control Valves," helpful in addressing some aspects of the two phase flow analyses. (Note: the three items listed above were not addressed in the licensee's assessment of two phase flow, and these items are important considerations for assuring that system integrity will be maintained during two phase flow conditions.)

d. 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 Page 3 of 5 i

.. Attachmont 1 LR-N980325 and confirm that the FMEA is documented and available for review, or explain why a complete and fully documented FMEA was not performed.

e. Explain and justify all uses of engineering judgement.

PSE&G Response 3 '

As noted in the Request for Additional Information, this question is only applicable to those event scenarios where the occurrence of waterhammer has not been eliminated.

Since measures are in place to assure waterhammer will not occur, this question is not applicable to Hope Creek. Similarly, PSE&G has concluded that the measures

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established are adequate to prevent occurrence of two-phase flow conditions during and following all postulated accident scenarios.

NRC Question 4 Determine the uncertainty in the waterhammer and two-phase flow analysis, explain how the uncertainty was determined, and how it was accounted for in the analyses to assure conservative results for the Hope Creek plant.

PSEAG Response 4 As noted in the Request for Additional Information, this question is only applicable to those event scenarios where the occurrence of waterhammer has not been eliminated.

Since measures are in place to assure waterhammer will not occur, this question is not applicable to Hope Creek. Similarly, PSE&G has concluded that the measures established are adequate to prevent occurrence of two-phase flow conditions during and following all postulated accident scenarios.

NRC Question 5 Confirm that waterhammer and two phase flow loading conditions do not exceed any design specifications or recommended service conditions for the piping system and components, including those stated by equipment vendors; and confirm that the system will continue to perform its design basis functions as assumed in the safety analysis report for the facility, and that the containment isolation valves for the affected system will remain operable. J PSE&G Response 5 i

As noted in the Request for Additional Information, this question is only applicable to those event scenarios where the occurrence of waterhammer has not been eliminated.

Since measures are in place to assure waterhammer will not occur, this question is not Page 4 of 5

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.. Atta*hment 1 LR-N980325 applicable to Hope Creek. Similarly, PSE&G has concluded that the measures estaNished are adequate to prevent occurrence of two-phase flow conditions during and following all postulated accident scenarios.

NRC Question 6 Provide a simplified diagram of the affected system, showing major components, active components, relative elevations, lengths of piping runs, and the location of any orifices and flow restrictions.

PSE&G Response 6 A simplified diagram is enclosed as Attachment 2 to this submittal.

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