ML20210H973

Summary of 860204-05 Meetings W/Util & Franklin Research Ctr Re Winds/Tornadoes Pra.Preliminary Staff Questions & List of Attendees Encl

ML20210H973
Person / Time
Site:	Yankee Rowe
Issue date:	03/27/1986
From:	Clifford J Office of Nuclear Reactor Regulation
To:	Office of Nuclear Reactor Regulation
References
NUDOCS 8604030289
Download: ML20210H973 (13)

Text

l 8 jg UNITED STATES P o NUCLEAR REGULATORY COMMISSION 5  : E WASHINGTON. D. C. 20555

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W3 2 7 1966 Docket No.50-029 LICENSEE: Yankee Atomic Electric Company (YAEC0)

FACILITY: Yankee Nuclear Power Station

SUBJECT:

Meeting Summary - Meeting with YAECO on Winds / Tornadoes Probabilistic Risk Assessment (PRA)

A meeting was held on February 4,1986 and February 5,1986, between members of the NRC staff and personnel from YAECO. The portion of the meeting on February 4, 1986 was held at the site to conduct a walkdown of the structures, systems and components that could be affected by high winds or tornadoes. The portion of the meeting on February 5,1986 was held at the YAECO Corporate Offices in Framingham, Massachusetts to discuss a list of preliminary questions from the staff (Enclosure 2), and to evaluate calculations supporting the YAECO PRA for the SEP topic on winds and tornadoes. A list of attendees is provided in Enclosure 1.

The following areas of the plant were looked at during the plant walkdown:

the turbine building, including the main feedwater regulating valves and associated shielding structures and components; the turbine building west staircase (used for operator egress from the control room); the switchgear room

! (including station batteries #1 and #2); the non-return valve enclosure; the cable tray house; the auxiliary boiler room; the upper primary auxiliary building; the diesel generator building (including emergency core cooling l

pumps); the dedicated safe shutdown building; and the exterior of the vapor l container.

l i s. portion of the meeting that took place on February 5, 1986 concentrated j on discussions regarding the questions included as Enclosure 2 to this meeting sunnary. As part of its responses, the licensee emphasized the following points:

1. Any discussion or review of the details of the winds / tornadoes PRA

should be conducted within the context of the overall risk of the plant. The licensee emphasized the small core size and low l population density surrounding the plant as two significant issues l

to be considered. Thus, for example, the licensee felt that upgrading i the diesel generator west wall would not significantly change the overall risk.

8604030289 DR 860327 p ADOCK 05000029 PDR I >

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2. In response to the NRC concern regarding the completeness of the YAEC0 approach, the licensee provided an explanation of their Critical Safety Function (CSF). approach to responding to emergency conditions. In the CSF approach, the systems required to maintain those critical functions necessary for plant safety are determined, and then the fault trees are further developed to determine the structures and components that could impact the operability of the systems. YAEC0 stressed that while this approach may not conform to a traditional fault tree development process, assurance of safe operation should be provided through the determination that the CSFs are' maintained.

Additional discussions were held regarding the construction of various roofs and walls throughout the Yankee site.

The_ questions listed in Enclosure 2 were used by the NRC reviewers to gain

' insight into the YAEC0 winds / tornadoes PRA during the meeting. The NRC reviewers stated that a detailed review of the PRA was to be conducted, and a fonnal list of questions would be forwarded when the review was completed.

The formal list of questions may include some of the questions listed in Enclosure 2 for which the staff needs formal responses.

James W. Clifford, Project Manager Project Directorate #1 Division of PWR Licensing-A

Enclosures:

1. List of Attendees

2. Preliminary Staff Questions cc w/ enclosures:

see next page See previous concurrences.*

Office: PM/ PAD #1 RRAB ISAPD PD/PD#1 Surname: JClifford*/tg:jm MFields* -PYChen* Glear*

Date: 03/11/86 03/18/86 03/ZW86 03/13/86

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Mr. George Papanic, Jr.

Yankee Atomic Electric Company Yankee Nuclear Power Station cc:

Mr. James E. Tribble, President Yankee Atomic Electric Company 1671 Worcester Road Framingham, Massachusetts 01701 Thomas Dignan, Esquire Ropes and Gray 225 Franklin Street Boston, Massachusetts 02110 Mr. N. N. St. Laurent Plant Superintendent Yankee Atomic Electric Company Star Route Rowe, Massachusetts 01367 Chairman Board of Selectmen Town of Rowe Rowe, Massachusetts 01367 Resident Inspector Yankee Nuclear Power Station c/o U.S. NRC Post Office Box 28 Monroe Bridge, Massachusetts 01350 Regional Administrator, Region 1 U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pennsylvania 19406 Robert M. Hallisey, Director Radiation Control Program Massachusetts Department of Public Health 150 Tremont Street, 7th Floor Boston, Massachusetts 02111

ENCLOSURE 1 LIST OF ATTENDEES SEP WINDS /TORNAD0ES PRA MEETING NAME AFFILIATION J. Clifford NRC/ PAD #1 M. Fields NRC/DSR0/RRAB P. Y. Chen NRC/ISAPD Vu Con- Franklin Research Center

, J. Hazeltine YAEC/ Project Manager G. Papanic YAEC/ Project Engineer S. Shultz YAEC Bruce Holmgram YAEC Donald Le Francois YAEC S. Follen YAEC J

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ENCLOSURE 2 STAFF PRELIMINARY QUESTIONS REGARDING THE YANKEE WIND / TORNADO HAZARD ANALYSIS

REFERENCE:

Tornado Cost-Benefit Analysis for Proposal Backfits at Yankee Nuclear Power. Station, September 1984 Questions / Comments

1. The cost / benefit study was limited to the structures identified on page 150. How was the possible benefit of modifying other "wcak" structures (e.g., the diesel generator building west wall) determined?

2. Figures 3-4 thru 3-6 depict the event trees used in this study and were based on studies of internal initiating events occurring randomly. High wind / tornado events have the potential for causing mul_tiple system failures of diverse locations almost simultaneously. It needs to be demonstrated that the method used in this study includes all combinations of structural failures leading to system failures that could have a.

significant impact on the overall core melt frequency. As an example, consider the possibility of a station blackout resulting from a high (110 mph) wind resulting in the loss of offsite power, all three emergency diesels (due to the collapse of wall 011053 and the interior walls between the diesels) and a random failure of the SSS dedicated diesel.

One possible way of identifying all possible core melt sequences would be

-2 to examine which systems could fail at various wind speed and then determine the potential of these system failures leading to core melt.

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3. A detailed discussion is needed of the manner in which collapsing walls and roofs affect systems within. Specifically, discuss the following:

a) The wind / tornado loads on interior walls and systems given that an exterior wall / roof has failed needs to be defined. The potential effects for interior damage needs to be included in the core melt analysis.

b) For those situations where not all equipment inside a room is j assumed destroyed following the failure of a wall or roof, additional justification will be needed.

j. c) Justify the assumption stated on page 99 that the clad (block) walls will fall in the equivalent of the wall height from its l footing.

4. Regarding the potential effects of collapsing walls and roofs, respond to the following questions:

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a) Page 31. Does the analysis assume that the 480V AC Bus in the safety injection room will not fail due to any conceivable wind hazard?

b) Page 33. Discuss further the assumption made that the failure of the upper level primary auxiliary building west wall will not lead to any system failures.

c) Page 33. Elaborate on why the safety injection (SI) line will not

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be damaged by collapsing walls and how the SI lines will protect the electric emergency feed pump piping.

d) Page 33. Discuss the possibility of impacting equipment in the primary auxiliary cubicle area due to the failure of the auxiliary, building roof.

e) Page 100. For critical area ABR explain why wind could not impact the interior walls given that the exterior wall has collapsed.

f) Page 100. Why doesn't the failure of the cable tray house roof have a significant impact on the cabling within this area?

g) Page 101. Elaborate on the reason given for not providing wind

loadings on the interior walls of the diesel generator building.

The assumption that the high uind/ tornado event is too short to affect internal walls is questionable.

h) Page 101. For critical area LLPAB describe in more detail the protection afforded by the adjacent rooms to the east and west walls and also on the spacial protection assumed for the north wall failure consequences. Explain why the north wall failure will not affect the 4" recirculation piping.

1) Page 102. Explain why a SIB west wall failure will only affect the

1. 3 train of SI pumps.

j) Page 104. Explain in more detail point 2.

k)- Page 104. Regarding point 3, is the consequence of losing all DC power severe enough to consider including the failure (at higher wind speeds) of this area in the analysis?

1) Page 104. Elaborate on the information provided in point 1.

m) Page 105. Explain why failure of the ULPAB roof will not impact the blowdown header or connecting piping.

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5. Provide the external design pressure of the vapor containment and discuss the effects, if any, of a pressure drop of several psi due to a tornado on the' containment.

6. Page 31. Is it possible for an electrician to remove a portion of bus bar in the station service transformer yard during a high wind / tornado event?

7. Page 32. What protection is afforded to the electric emergency feed and charging to main feed path as well as the main feed lines?

8. Page 34. Describe the wind hazard protection available for the non-return valve platform.

9. Page 34. How was the loss of the turbine building west staircase factored in on operator actions outside the control room?

10. Page 69. Provide the power sources that allow remote operation of FW isolation.

11. Page 69. Explain in detail tha steps an operator must take to isolate the steam lines upon loss of DC Bus No. 1. Include the adverse effects of high wind / tornado loads.

12. Page 70. Since assuming loss of offsite power when loss of DC Bus No. 1 occurs may not be conservative, discuss the possibility and potential effects of losing just the DC Bus No. 1.

13. Page 70. Events 1 and 2 are not considered possible because wind speeds have to exceed 250 mph before failure of the containment fails. Discuss the potential of failing these lines outside the containment.

14. Page 71. Provide information on any possit,le cutside containment

isolation valves whose wind induced failure could affect the core melt frequency.

15. Page 74. What is the probability, and effects of, a main coolant system loop safety valve mechanically failing open?

16. Page 79. How valid is the implieo assumption that the PORV will be needed just once, if at all, during al1 the core melt sequences?

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17. Page 88. Its stated that PORV power is modeled as always being available l to increase the chance of a small LOCA. What are the consequences of i

having to-rely on higher pressure setpoint relief valves to protect the reactor coolant system from over pressure?

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18. Page 102. Does station blackout follow from. failure of SIBN and loss of off-site power?

19. Page 105. The failure probability of the station service transformer support structure seems to be independent of wind speeds. Please explain.

20. Page 105. It is not clear that the fuel oil tank would not be needed following on extended loss of off-site power event. Provide the high wind / tornado capacity of this tank.

21. Pages 105-106. More justification in terms of quantification of the risks involved is required for not modeling the following arecs:

a) Under the VC.

b) Pump room, and the c) Upper level primary auxiliary building west wall.

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22. How long can the emergency DC batteries work following loss of all AC power?

23. Page 150. Provide a breakdown of the costs involved for the 10-5 modification case.

F 24.- The tables of core melt frequency vs. wind / tornado speed intervals in Section 6.6.2 need further explanation. For example, the wind speed interval of 103 pmh to - results in a core melt probability of 2.0 x

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10-2 . Since for high enough wind speed the core melt frequency model will be 1.0, there must exist an unidentified wind speed upper limit.

w-f5dk 2 71986 DISTRIBUTION:

l Docket Files-NRC PDR" Lecal POR G. Lear J. Clifford OELD E. Jordan B. Grimes ACRS (10)

NRC Participants PD#1 r/f PD#1 s/f 4