ML20043H113

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
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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, ', VinomiA F,LucTurc AND POWEH COMPM

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

+ Attention: Document Contro! Desk NL&P/RMN "g / ~ Washington; D.C. 20555 Docket Nos. 50-338

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6 Gentlemen: y g+4 .:/:

M . 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 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

,' ' risk from loose parts'is sufficiently small that the precautionary removal of undamaged

[j ,; , " 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

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

.(1 I - LPMS' has . failed and,will be . removed ,The remaining thermal sleeves .will be i'adiogmphed every third refueling outage.

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

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1982= and Octobor 12,1982 letters and your January 11, 1983 Safety Evaluation-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

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

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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 '

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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 7 .

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

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ff vibratory cycles. Figure l-9.2.Fof Appendix I to~ Section lll of the ASME Boiler and Prossure Vessel Code shows the design fatigue curves for this material. The curves '

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', show that ifcthe, holds do not fail early (before 100 million cycles), they are not t > -

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

1 Thermal cycle fatigue was evaluated using three dimensional finite element stress l

. analysis. The' cumulative fatigue damage was summed for all transients expected over l 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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