ML20043H113

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Concludes That Removal of Temporary Loose Parts Monitoring Sys Does Not Increase Probability of Acccident,Create Possibility of New Kind of Accident & Does Not Reduce Margin of Safety
ML20043H113
Person / Time
Site: North Anna  Dominion icon.png
Issue date: 06/15/1990
From: Stewart W
VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
90-095, 90-95, NUDOCS 9006220023
Download: ML20043H113 (2)


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].T VinomiA F,LucTurc AND POWEH COMPM S

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' June 15,1990 '

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U.S. Nuclear Regulatory Commissan Serial No.90-095

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Attention: Document Contro! Desk NL&P/RMN "g

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~ Washington; D.C. 20555 Docket Nos.

50-338 50-339

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6 Gentlemen:

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. yJBGINIA;E' ECTRIC AND POWER COMPANY NORTH ANNA POWER STATIOfU) NITS 1 AND 2 M.,

BEMOYAL OF TEMPORARY LOOSE PARTS MONITORING SYSTEM

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.in 1982 Virginia Electric and Power Company found that some of the thermal sleeves

.c in'the reactor coolant system at North Anna Power Station Units 1 and 2 had cracked A ' welds or were displaced. The.'affected sleeves were removed and in our letters dated L

' August.4,1982 and October 12,1982, we committed to examining the remaining

-sleeves during subse~quent refueling outages and using a temporary loose parts i& n, monitoring system-(LPMS) until they are removed. We-havo since detennined that the

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risk from loose parts'is sufficiently small that the precautionary removal of undamaged sleeves and the use of.the temporary LPMS is not needed. This is based on the small 3 yC '

(consequences of a loose sleeve, the low probability of fu?ure slesvo failures and the

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, fact that the regularLPMS has a,high probability ~of detecting a failure. The ternporary.

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- LPMS' has. failed and,will be. removed,The remaining thermal sleeves.will be I

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i'adiogmphed every third refueling outage.

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The consequences of loose sleeves have already been discussed in our August 4, Q'#'

1982= and Octobor 12,1982 letters and your January 11, 1983 Safety Evaluation-f f ;I Report., Generally,.a sleeve weld fallure will,not cause any significant damage. The M

j worst result would be if the _14 inch' surge line sleeve-were.to shear the T-hot

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t thermowell This would cause'a leak that is less than the capacity of one charging pump. The resulting jet impingement and potential missile would not affect safety f-

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%o' related equipment.! A loose sleeve could a!so restrict coolant flow to the fuel. However,

@1 isince the sleeves are curved. the flow would not be completely blocked and the DNBR 4

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? Would not be significantly' reduced.;

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i/, Mbratory arid thermaf fatigue analysis of the thermal.slee'ves show that future failures

$@ ff vibratory cycles. Figure l-9.2.Fof Appendix I to~ Section lll of the ASME Boiler and 7

are very unlikelyf Calculations show'that the sleeves have endured over 80 billion n/g ' '

Prossure Vessel Code shows the design fatigue curves for this material. The curves M; i show that ifcthe, holds do not fail early (before 100 million cycles), they are not y

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expected to fall due to fatigue. This is consistent with our observations. No cracks or defects have been found since 1982.

Thermal cycle fatigue was evaluated using three dimensional finite element stress

. analysis. The' cumulative fatigue damage was summed for all transients expected over 40 years of operation and found to be acceptable.

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- North Anna _ does have a permanent LPMS as required by Unit 1_ Technical Specification'3/4.3.3.9. Although there is no corresponding Unit 2 Specification, this is a shared system and the Unit 1 Specification is treated as if it were applicable to both Units.,This system is adequate for detecting loose thermal sleeves.

We have therefore concluded that the removal of the_ temporary LPMS does not increase the probability or consequence of an accident, does not create the possibility of_a new or different kind of accident, and does not reduce the margin of safety.

If you have any questions or require additionalinformation, please contact us.

Very truly_yours, N

W. L. Stewart

. Senior Vice President Nuclear

-i ccf U.S. Nuclear Regulatory Commission Region 11 101 Marietta Street, N.W.

Suite 2900 Atlanta, Georgia 30323 Mr. M. S.' Lesser-NRC Senior Resident inspector North Anna Power Station 1

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