ML20236M659
| ML20236M659 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 07/10/1998 |
| From: | Croteau R NRC (Affiliation Not Assigned) |
| To: | Maret G VERMONT YANKEE NUCLEAR POWER CORP. |
| References | |
| GL-96-06, GL-96-6, TAC-M96880, NUDOCS 9807140189 | |
| Download: ML20236M659 (5) | |
Text
_
=
July 10, 1998 Mr. Gregory A. Maret Director of Operations Vermont Yankee Nuclear Power Corporation 185 Old Ferry Road Brattleboro, VT 05301
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION REGARDING GENERIC LETTER (GL) 96-06 AT VERMONT YANKEE NUCLEAR POWER STATION (TAC NO. M96880)
Dear Mr. Maret:
By letters dated October 30,1996, January 28,1997, and February 9.1998, you provided information related to GL 96-06, " Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions," dated September 30,1996.
GL 96-06 included a request for licensees to evaluate cooling water systems that serve containment air.colers to assure that they are not vulnerable to waterhammer and two-phase flow conditions. In order to complete our review of these issues, additionalinformation is necessary. Please provide the additional information requested by the enclosure to this letter by September 30,1998, to support the review schedule for GL 96-06.
If you should have any questions regarding this request, please contact me at (301) 415-1475.
Sincerely, Original signed by Richard P. Croteau, Project Manager Project Directorate 1-3 Division of Reactor Projects - 1/II Office of Nuclear Reactor Regulation Docket No. 50-271
Enclosure:
Request for Additionalinformation cc w! encl: See next page
,s.
DISTRIBUTION
}
Docket File C. Cowgill R. Croteau PUBLIC A. Lee T. Clark Vermont Yankee r/f ACRS J. Tatum J. Zwolinski OGC DOCUMENT NAME: G:\\Croteau\\M96880.RAI To receive a copy of this document, indicate in the box:
"C" = Copy without attachment / enclosure "E" = Copy with attachment / enclosure "N" = No copy OFFICE PDI-3/PM Mry l l PDI-3/LA
.e f,q ltj l
PDI:3/D
-l l
NAME RCroteau p'
TCtark Wb CTh@ 4 DATE
' l/ / 4 /98
'// /D /98
/
/98 4//[ /98 OFFICIAL RECORD COPY
/,/
9 rmw3 r 1 r" (P*r"Nm p q 5W 9807140189 980710 V'
- L g a m.a _ u L. d g PDR ADOCK 05000271 p
PDR C
G. Maret Vermont Yankee Nuclear Power Station oc'.
Regional Administrator, Region i Mr. Raymond N. McCandless U. S. Nuclear Regulatory Commission Vermont Division of Occupational 475 Allendale Road and Radiological Health King of Prussia, PA 19406 Administration Building Montpelier, VT 05602 Mr. David R. Lewis Shaw, Pittman, Potts & Trowbridge Mr. Gautam Sen 2300 N Street, N.W.
Licensing Manager Washington, DC 20037-1128 Vermont Yankee Nuclear Power Corporation Mr. Richard P. Sedano, Commissioner 185 Old Ferry Road Vermont Department of Public Service Brattleboro, VT 05301 120 State Street,3rd Floor Montpelier, VT 05602 Resident inspector Vermont Yankee Nuclear Power Station Public Service Board U. S. Nuclear Regulatory Commission State of Vermont P.O. Box 176 120 State Street Vemon, VT 05354 Montpelier, VT 05602 Mr. Peter LaPorte, Director Chairman, Board of Selectmen ATTN: James Muckerheide Town of Vemon Massachusetts Emergency Management
)
P.O. Box 116 Agency Vemon, VT 05354-0116 400 Worcester Rd.
P.O. Box 1496 Mr. Richard E. McCullough Framingham, MA 01701-0317 Operating Experience Coordinator Vermont Yankee Nuclear Power Station Jonathan M. Block, Esq.
P.O. Box 157 -
Main Street Govemor Hunt Road P. O. Box 566 Vemon, VT 05354 Putney, VT 05346-0566 G. Dana Bisbee, Esq.
Mr. Michael J. Daley Deputy Attomey General Trustee and Legislative Representative 33 Capitol Street New England Coalition on Nuclear Concord, NH 03301-6g37 Pollution, Inc.
Box 545 Chief, Safety Unit Brattleboro,VT 05301 Office of the Attomey General One Ashburton Place,19th Floor Boston, MA 02108 l
Ms. Deborah B. Katz I
Box 83 Shelbume Falls, MA 01370 1
l
. O, REQUEST FOR ADDITIONAL INFORMATION FOR RESOLUTION OF GL 96-06 ISSUES AT VERMONT YANKEE (TAC NO. M96880)
Generic Letter (GL) 9S-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 that they are not vulnerable to waterhammer and two-phase flow conditions. The Vermont Yankee Nuclear Power Corporation (the licensee) provided its assessment of the waterhammer and two-phase flow issues for the Vermont Yankee plant in letters dated January 28 and February 9,1997. The licensee concluded that waterhammer was not likely to occur in the 1
reactor building closed cooling water (RBCCW) system, which provides cooling water to the containment air coolers (CACs), following a loss-of-coolant accident (LOCA) coincident with a loss-of-offsite power (LOOP). For the main steam line break (MSLB) scenario, the licensee I
concluded that there was a possibility that waterhammer could occur in the RBCCW system, but that the transient loads would be less than the piping failure limits. The CACs at. Vermont Yankee are not safety-related and are not credited for accident mitigation. In order to assess the licensee's resolution of these issues, the following additionalinformation is requested:
Notes: a. Information that has been submitted previously may be referred to and supplemented as necessary to provide a complete response to the staff's questions.
- b. To the extent that positive measures are implemented to eliminate the potential for waterhammer and two-phase flow conditions, question numbers 2 and 3 may not be applicable.
- c. The following questions are applicable to the system configuration and analyses that are credited for the final resolution of the waterhammer and two-phase flow issues.
1.
Provido 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 sce'narios should be considered, as well as temperatures, pressures, flow rates, load combinations, and potential component failures. For the LOCA scenario, identify the maximum amount of steam that could be generated, and explain why this amount of steam does not constitute a waterhammer concem. Also, while heat transfer considerations may not be of concem for the two phase flow issue, structural and system integrity considerations must still be addressed (this aspect of the two-phase flow issue was not addressed in the licensee's submittals). For example, the following two-phase flow effects are relevant:
the consequences of steam formation, transport, and accumulation; Enclosure
t 2
cavitation, resonance, and fatigue effects; and erosion considerations.
Licensees may find NUREG/CR-6031, " Cavitation Guide for Control Valves," helpful in addressing some aspects of the two-phase flow analyses. To the extant that the possibility for waterhammer and two-phase flow to occur are eliminated, describe the minimum margin to boiling that will exist.
2.
If a methodology other than that discussed in NUREG/CR-5220. " Diagnosis of Condensation-induced Waterhammer," or in EPRI NP-6766, " Water Hammer Prevention, Mitigation, and Accommodations," was used in evaluating the effects of.
waterhammer, describe this altemate methodology in detail. Also, explain why this methodology is applicable and gives conservative results (typically accuinpiished through rigorous plant-specific modeling, testing, and analysis).
3.
Identify any computer codes that were used in the waterhemmer 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).
4.
Describe and justify all assumptions and input parameters (including those used in any computer codes) that were used in the waterhammer and two-phase flow analyses, and provide justification for omitting any effects that may be relevant to the analyses (e.g.,
fluid st.ucture interaction, flow induced vibration, erosion). Confirm that these assumptions and input parameters are consistent with the existing design and licensing basis of the plant. Any exceptions should be explained and justified.
5.
Explain and justify all uses of " engineering judgement" that were credited in the waterhammer and two-phase flow analyses.
6.
Discuss specific system operating parameters and other operating restrictions that must be maintained to assure that the waterhammer and two-phase flow analyses remain valid (e.g., surge tank level, pressures, temperatures), and explain why it would not be appropriate to estabush Technical Specification requirements to acknowledge the importance of these parameters and operating restrictions. Also, describe and justify use of any non-safety related instrumentation and controls for maintaining these parameters.
7.
Implementing measures to assure that waterhammer will not occur, such as managing post-accident operation of the CACs or establishing and maintaining system overpressure requirements, 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 measurec that have been established (or will be established) are adequate to prevent the occurrence of waterhammer during (and following) all applicable accident scenarios.
_ _ _ _ _ _ - _ _ - _ - - - - - - - - - = = = - - -
l 0 3
8.
Confirm that the waterhammer and two-phase flow analyses included a complete failure i
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 wny a complete and fully documented FMEA was not performed.
9.
Describe the uncedainties that exist in the waterhammer and two-phase flow analyses, including uncertainties and shortcomings associated with the use of any computer codes, and explain how these uncertainties were accounted for in the analyses to assure conservative results.
10.
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.
11.
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.
h
_ _ _ _ _. - _ _ _ _ _. _ - _ - -