ML20217K127
| ML20217K127 | |
| Person / Time | |
|---|---|
| Issue date: | 04/23/1998 |
| From: | Wetzel B NRC (Affiliation Not Assigned) |
| To: | Modeen D NUCLEAR ENERGY INSTITUTE (FORMERLY NUCLEAR MGMT & |
| References | |
| GL-96-06, GL-96-6, NUDOCS 9805010100 | |
| Download: ML20217K127 (7) | |
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NUCLEAR REGULATORY COMMISSION U
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'E WASHINGTON, D.C. SpeeMooi April 23, 1998 i
l Mr. David J. Modeen Director, Engineering Nuclear Generation Division Nuclear Energy Institute l
1776 l Street, NW, Suite 400 Washington, D.C. 20006
SUBJECT:
CONTENTS OF REQUESTS FOR ADDITIONAL INFORMATION PERTAINING TO THE WATERHAMMER AND TWO-PHASE FLOW ISSUES IN GENERIC LETTER 95-06, " ASSURANCE OF EQUIPMENT OPERABILITY AND CONTAINMENT INTEGRITY DURING DESIGN-BASIS ACCIDENT CONDITIONS"
Dear Mr. Modeen:
During telephone conversations between the Nuclear Energy Institute (NEI) and NRC staff on April 8 and April 10,1998, Mr. Kurt Cozens inquired about the staff's current review efforts associated with Generic Letter 96-06, " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions." Mr. Cozens was interested in the information requests that were being issued to licensees regarding resolution of the waterhammer and two-phase flow issues, and asked if the NRC could provide a description of the information being requested oflicensees. Mr. Cozens was considering whether it would be feasible to develop an industry initiative for responding to the staff's request for information. The NRC encourages licensees to work as a group in establishing responses to the staff's information requests as long 3
as substantial schedular delays do not occur.
j in response to Mr. Cozens' request, the NRC is currently preparing requests for additional information (RAls) for the waterhammer and two-phase flow issues to assure that these issues have been adequately addressed by licensees. These requests depend on the specific response that was received from each licensee and whether the fan coolers will be used (either as a requirement for accident mitigation or as an option) such that waterhammer could conceivably occur. The goal of the RAls is to establish a high level of confidence that analyses have been performed in a rigorous and conservative fashion, that licensing basis requirements have not been compromised, that NRC review and approval of plant modifications have been requested (if appropriate), and that additional Technical Specification requirements have been proposed if 1\\
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l warranted for maintaining critical system' parameters. While the RAls are plant-specific, enclosed are tWo examples which attempt to capture the essence of the staff's information request.
If you have any further questions regarding these RAls, contact me at (301) 415-1355.
Sincerely, ORIGINAL SIGNED BY Beth A. Wetzel, Senior Project Manager Project Directorate lll-1 Division of Reactor Projects-lll/IV
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Mr. Kurt Cozens Nuclear Generation Division Nuclear Energy institute 1776 i Street, NW, Suite 400 Washington, DC 20006 i
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Contents of RAls Examole 1 For those plants where the fan coolers will be (or may be) used post-accident and wcterhammer is a possibility, the questions will be along the following lines:
1.
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 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.
For both the waterhammer and 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 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) 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).
c.
Provide a detailed c'escription 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. Additional examples include:
the effects of void fraction on flow balance and heat transfer; the consequences of steam formation, transport, and accumulation; cavitation, resonance, and fatigue effects; and erosion considerations.
a Licensees may find NUREG/CR-6031, " Cavitation Guide for Control Valves,"
helpfulin addressing some aspects of the two-phase flow analyses. (Note: 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.)
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Confirm'that the 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 e.
Explain and justify all uses of " engineering judgement."
3.
Determine the uncertainty in the waterhammer and two-phase flow analyses, explain how the uncertainty was determined, and how it was accounted for in the analyses to assure conservative results.
4.
Confirm that the 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.
5.
Provide a simplified diagram of the system, showing major components, active components, relative elevations, lengths of piping runs, and the location of any orifices and flow restrictions.
Examole 2 For those plants that do not intend to use the containment fan coolers for accident mitigation, the questions are along the following lines:
1.
Describe measures that have been (or will be) taken to assure that plant operators will not use the containment /drywell coolers as an option during accident conditions.
2.
Implementing measures to assure that waterhammer will not occur, such as prohibiting post-accident operation of the affected system, is an acceptable approach for addressing the waterhammer concem. However, all scenarios must be considered to assure that the vulnerability to waterhammer 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 the occurrence of waterhammer during (and following) all postulated accident scenarios.
3.
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 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).
Note: This question is only applicable to those event scenarios where the
, occu nce of waterhammer has not been eliminated (see question 2, abovej.
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- 4.
For both the waterhammer (if applicable as discussed in the note following question 3, above) 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 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) 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 justificati0n ict omitting any effects that may be relevant to the analysis (e.g., fluid structure interaction, flow induced vibration, erosion).
c.
Provide a detailed description of the " worst case" scenarios for waterhammer arid two-phase flow, taking into consideration the complete range of event possibili'.les, system configurations, and parameters. For example, all waterhammer typ9s and water slug scenarios should be considered, as well as temperatures, pressures, flow rates, load combinations, and potential component failures. Additional examples include:
the effects of void fraction on flow balance and heat transfer; i
the consequences of steam formation, transport, and accumulation;
+
cavitation, resonance, and fatigue effects; and
+
erosion considerations.
Licensees may find NUREG/CR-6031, " Cavitation Guide for Control Valves,"
helpfulin addressing some aspects of the two-phase flow analyses. (Note: It is important for licensees to realize that in addition to heat transfer considerations, two-phase flow also involves structural and system integrity concerns that must be addressed.)
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 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."
5.
Determine the uncertainty in the waterhammer (if applicable as discussed in the note following question 3, above) and two-phase flow analyses, explain how the uncertainty was determined, and how it was accounted for in the analyses to assure conservative results.
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6.
Confirm that the waterhammer (if applicable as discussed in the note following question 3, above) 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 l
containment isolation valves will remain operable.
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Provide a simplified diagram of the affected system, showing major components, active l
ccmponents, relative elevations, lengths of piping runs, and the location of any orifices and flow restrictions.
l i-Also, as part of our review, we will be questioning the need for NRC review and approval of any 1
modifications that were made to address these issues, and we will be questioning the need for p
additional Te:hnical Specification requirements to include system parameters (e.g., temperature, pressure, level) that may be important for maintaining operability. You should also be aware that in addition to the information requests that are being issued for the waterhammer and two-phase flow issues, information requests are also being issued to obtain additional information about l
licensee resolution of the thermal overpressurization concem. In general, these requests are being issued as separate RAls.
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