ML20024G341
| ML20024G341 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 02/14/1975 |
| From: | Ziemann D Office of Nuclear Reactor Regulation |
| To: | Mayer L NORTHERN STATES POWER CO. |
| References | |
| NUDOCS 9102110329 | |
| Download: ML20024G341 (5) | |
Text
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1, Di=TRIBITTION:
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Glainas NRC'PDR LSlegers Local PDR CDeBevec FEB 1 1975 Docket rite o%'N1 %
Docket Fo. 50-2t3 l
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DLZiemann i
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ht. L. O. Nayer
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Director of Uucts Sept.rt c
5 Eervices RMDiggs 414 Nicolle ksit JRBEuchanan TBAbernathy Minnespolis, Finnesota
$501 Svarga Centlenent LShao Schan Luperiences at various IM plants with hark 1 Conteinocets have shown that danage to the tores st ructure car. occer troo two dif ferent phenevena associated witt reliet velve operat tors.
Demare car result frcm the force exerted on the discherpe air and steessstructure when, on first opening, relici valves into the torus water.
This phenor.cnon is ref erred to as stean vent clearint.
Tamagc also can result f ruer torus vibrations l
v5ich accoeracy extcoclec rellet valve dischstre into the torus water or the flow frot tne drywell dutier a LOCA it the pool water is at elevated t empe r at ure s.
%is etfeet is knovn as the steam quenchirr vibration phenowenon.
These wheno ena are discussed below.
[t,ga,n Vent Clespne Qenomenon The tark I torus structure of some boiling voter resetcr plants was found te he defective following cycles of steau vent elsaring into the torus when prietary system rellei valves opened.
Investiltation indicated that sorse of these plante may cot have been designed to v that, sed this phenomenon 8
throorhout the life of the plant when the torus was nue.ber of tellei valve openings.
subjested to a predicted The Cuad Cities Lett 2 end the Erowns lerry Uvit 1 torus structures were subjected to teets when defects or exceesive noise and vibrations were discovered follcwine the above puenezecon. (1)(2)
As a result of these tests, some codifications to the torus structures were eade f or these fecilitie* end som sinitar facilities, tecause of the arterent progressive r.etitre et.nc a.arerial f atig ue t y pe of feilure pheno-econ, we do not believe that there is any Imediate potertial hstert;; however, w presently do not (i)~IlliF IOf5 F 5tE T Vent Cicoriep theromena and Structural Respones of the FE Torus (Mark I Contale.asnt)", Ceneral Electric Company.
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(2) "1573 trowns Ferry l' cit 1 Torus Experience" submit ted ' by the Tennessee Valley Authority to the Office of Repulation, hay 7, 1974.
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"' Form AEC.31s (Rev. S-53) AECM 0240 fr u a sovsn=esamt eniavmo omas i.ts-4.. ass 9102110329 750214 PDR ADOCK 05000263 P
Morthern States Power Company FEB 141975 have the necessary assurance that the torus structures 1 maintain their integrity throughout the entire life of the facilities.
Steam Ouenchine vibration Phenomenon Elevated torus pool temperatures during extended relist valve operation have 'become of concern in light of occurrences at two Epropean reactors as reported to us by the General Elect ric Company. (4)(5) with local torus pool temperatures in excess of about 170F, due to prolonged relief valve j
operation, it was observed that severe torus structural vibrations occurred with moderate to high relief valve flow rates.
CE reported that these vibrations were caused by a steam condensinF mode characterized by periodic pulsetion of the steam jet at the relief valve discharpe point.
If allowed to continue, the vibrations could have resulted in st ructural damage to the torus due to material f atigue.
The probability for this vibration phenomenon from extended relief valve operation is considered to be low in view of operating limits imposed by current technical specifications.
'Ihe exist ing technical specifications on torus pool teciperatures generally limit nomal power operations to 90-95F with a raximum short tern limit of 120-130F.
liovever, occasions have arisen when a relief valve remained open f or extended periods resultine in elevated pool tempetatures and creating the potential for the steam quenching vibration phenomenon.
Requested Action In view of the foregoing considerat ions, we request that the following action Le initiated.
l 1.
For the Steam Vent Clearing Phenomenon, a program should be developed for our review that la directed toward establishing the continuing l
integrity of the torus of your plant.
You should consider at least the following in developing your program:
(a) The need for verification tests.
(b) The need f or physical codifications to improve capability I
of the torus structure.
[3) Letter, I. Stuart, CE Company from W. Eutler, AEC, dated September 12, 1974.
t (4)* Letter, E. C. Case, USAEC, from I. F. Stuart, GE Company dated l
Novenber 7, 1974.
l 1
j (5) Letter, E. C. Case, USAEC, from I.
F. Stuart, CE Company dated December 20,1 974.
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Form AEC-31s (Rn. 9-53) AECM 0240 W lia covanneswt nmemo ornes io n-....as s
,t Northern States Power Company FEB : ; W3 (c) The torus fatigue characteristics when subjected to forces resulting from opening of relief valves.
(d) The predicted maximum number of relief valve openings, singly and collectively, during plant life.
s (e) Surveillance requirement s, including frequency of inspections, for verification of torus structural inteFrity.
2.
For the steam quenching vibration phenomenon, operating procedures should be developed..*nd changes to the Technical Specifications should be f.roposed to preclude the development of elevated temperatures of the torus pool water and provide for inspection of the torus as appropriate to identify any damage in the event of an extended relief valve operation.
In this ef fort, consider the results of your review required by Reguletcry OperationsBulletin 74-14. "FWR Relief Valve Discharge to Suppression Pool", dated November 11, 1974, and the interim recommendat!.ons of the General Electric Company to EWh ovners (References 4 and 5).
3.
Submit a description of your proFram and your proposed changes to the Technical Specifications. A suggested review schedule with major milestones and dates ir enclosed for your consideration; if these dates are not satisfactory, aJjustments may be possible af ter discussion with us.
If you do not intend to initiate a program for verification of the torus and/or proposed surveillance requirements, we require that you submit approprista justificatlon.
Your submittals are requested in accordance with the proposed schedule.
Three signed and notarized originals and thirty-seven (37) copies of your subrait tals are needed for our review.
Sincerely, o g na rh ned by Dennis L 3!mann Dennis L. Ziemann, Chief Operating Reactors Branch (2 Division of Reactor Licensing
Enclosure:
Proposed Schedule of Major Activities This request for generic information was approved' by GAD under a blanket clearance number B-180225 (R0072); this ecj clearance expires July 31, 1977.
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D' O Form AEC.318 (Rev. 9 53) AECM 0240 C v e novam. swr enmemo ornce ist,-as nus
l Northern Stctes Pow 2r Company I L c ', ' i'75 cc w/ enclosures:
Arthur Renquist, Esquire The Environmental Conservation Vice President - Law Library Northern States Power Company Minneapolis Public Library 414 Nicollet Mall 300 Nicollet Mall Minneapolis, Minnesota 55401 Minneapolis, Minnesota 55401 I
Gerald Charnof f Shaw, Pittman, PottJ, Trowbridge and Madden l
910 - 17th Street, N. W.
Washington, D. C.
20036 l
i Howard J. Vogel, Esquire Legal Counsel 2750 Dean Parkway Minneapolis, Minnesota 55416 Steve Gadler, P. E.
l 2120 Carter Avenue St. Paul, Minnesota 55108 Mr. Daniel L. Ficker Assistant City Attorney 638 City Hall St. Paul, tunnesota 55102 Ken Dzugan, Director-City of St. Paul Pollution Control Services 100 East 10th Street St. Paul, Minnesota 55108 Sandra S. Gardebring Special Assistant Attorney General Counsel for Minnesota Pollution Control Agency 1935 W. County Road B2 Roseville, Minnesota 55113 Anthony Z. Roisman, Esquire Berlin, Roisman and Kessler 1712 N Street, N. W.
Washington, D. C.
20036
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DiCLOSURE SCHEDULE OT ".AJOR AC_TIVITIEF TORUS STRUCTURE INTEGRITY Activity Date Letter to Licensees February 15, 1975 Responses of Licensees w/ Proposed Technical Specifications Revising Temperature Limits March 31, 1975 w/ Proposed Program for Maintaininr, Integrity of the Torus May 30, 1975 Review of Responses and Issuance of Technical Specification Changes on Tenperature Limits August 29, 1975 Qucctions to Licencecc Regarding Program for Maintaining Integrity of Torus September 26, 1975 Licensee's Response with Proposed Technical Specifications on Surveillance Requirements November 21, 1975 f
Review of Licensee's Response and Proposed Technical Specifications Surveillance Requirements January 2, 1976 Technical Specification Change on Surveillance Requirements Issued February 2, 1976 Expected Completion of Modifications February 2, 1976
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