B13610, Requests Relief from ASME Boiler & Pressure Vessel Code Section XI Requirements Re Mods to Pipe 3SWP-006-050-03. Results of Insps & Required Repairs Will Determine Schedule for Future Insps

Requests Relief from ASME Boiler & Pressure Vessel Code Section XI Requirements Re Mods to Pipe 3SWP-006-050-03. Results of Insps & Required Repairs Will Determine Schedule for Future Insps

ML20059A313
Person / Time
Site:	Millstone
Issue date:	08/15/1990
From:	Mroczka E, Sears C NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
B13610, GL-90-05, GL-90-5, NUDOCS 9008220205
Download: ML20059A313 (5)

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L L J (([',$'.C."'.* (203) 665-5000 i August 15, 1990 Docket No. 50-423 B13610 Re: ASME Section XI U.S. Nuclear Regulatory Commission ,

Attention: Document Control Desk  ;

Washington, DC 20555 l l

Gentlemen: 1 1

Millstone Nuclear Power Station, Unit No. 3  ;

Modification to Pipe 3SWP 006 050 03 I ILelief Reauest from ASME Code Section XI Reauirements In a letter dated April 20,1990,(I) Northeast Nuclear Energy Company (NNECO) submitted to the NRC Staff our generic position for dealing with interim 1 repairs of leaks in service water piping. Subsequent to this letter, the NRC  !

issued Generic Letter 90 05 which provides formal generic guidance on service water noncode repairs.

t The purpose of this letter is to request, in response to NRC Generic Letter 90 05, relief from ASME Boiler and Pressure Vessel Code Section XI require-ments pursuant to 10CFR50.55a(g)(6)(1). Attachment 1 provides a description of actions.taken by NNECO to make interim repairs to the leak in this piping ,

as an alternative to an IWA 4000 welded repair or an IWA-7000 replacement.

NNECO intends to proceed with the technical evaluation to ensure structural integrity, corrective action, and subsequent monitoring of routine repairs of erosion / corrosion damage in service water piping as outlined in our April 20, 1990 letteri- however, consistent with the provisions of the Generic letter, NNECO is submitting this relief request for temporary noncode repairs. The

Resident Inspector at Millstone Unit No. 3 has been informed of this repair,

and, as has been our practice, we will keep the Resident Inspector fully informed and current on all future repairs.

l (1) E. J. Mroczka letter to U.S. Nuclear Regulatory Commission, " Repairs to Service Water Piping," dated April 20, 1990.

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V.S. Nuclear Regulatory Comission B13610/Page 2 August 15, 1990 Please cmi'.act us if you have any questions.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY FOR: E. J. Mroczka Senior Vice President BY:

C. F. Sears Vice President cc: T. T. Mortin, Region 1 Administrator D. H. Jaffe, NRC Project Manager, Millstone Unit No. 3 W. J. Raymond, Senior Resident inspector, Millstone Unit Nos. 1, 2, and 3

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Docket No. 50-423 B13610 t'

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-j Attachment 1 Millstone Nuclear Power Station, Unit No. 3 Modification 3SWP 006-050 03

• o Request for Relief From ASME Code Section XI August 1990

p Attachment 1 B13610/Page 1 Millstone Nuclear Power Station, Unit No. 3 1 Leak in Pipe 35WP-006-050-03 >

Reauest for Relief From ASME Code Section XI Reouirements Backaround On July 27, 1990, Millstone Unit No. 3 observed leakage from a pipe flange adjacent to valve 35WP*V47. Piping inspection while replacing the gasket to stop the leak determined the leak was due to erosion / corrosion damage to the pipe under the lap joint flange. The area was inspected and measured using ultrasonic techniques. The data indicated that a pin hole leak existed in an area where wall thinning had occurred due to turbulence caused by the adjacent butterfly valve. The valve is part of a temperature control bypass and is automatically throttled to maintain constant temperature for the Control Building Air Conditioning System. The pipe is made of copper nickel and is subject to erosion / corrosion in areas of turbulence.

At this time, the leak has been stopped by placing rubber tape between the lap joint flange and the pipe.

Cmde Relief Reauested A one-time relief is requested from performing a repair to the requirements of ASME Code Section XI, Subsection IWA 400n; " Repairs," for this specific circumstance where repair material compatible with the piping systems is not available at this time. The repair will be performed when the repair mater-tais become available, but no later than the next refueling outage.

Basie for Relief I It was determined by engineering judgment, after a review of the stress l caiculation of record for this portion of the Service Water System (Stone and

Webster Calc.12179 NP8(B)-X53900, Rev. 3 including change notices), that the structural integrity of the piping is not considered to be adversely affected.

E The stress levels for SSE (faulted) conditions, from the calculation of record is 14 percent of the allowable at the affected area. Also if the overall pipe wall was to be reduced to 0.05 (min, wall - 0.04) inches, the resultant stresses for the SSE condition would be 35 percent of the allowable at the affected area. The no9inal wall thickness for this piping is 0.134 inches.

l Therefore, a significant margin of safety exists. Additionally, the hole I size, including- future predicted erosion, does not exceed the size at which run pipe stress intensification factors are required.

l In addition, this condition is considered acceptable on the basis of St.

l Venants principal. This principal states that small holes or weld fillets do not affect the stress distribution of the system. All restrictions involved with this )rincipal (diameter of hole < 3 percent of pipe circumference, noncrack-li(e and not in a tee or elbow) have been met.

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• l Attachment 1 B13610/Page 2

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The estimated erosion rate based on time in service is .003 inches per month.

Thus, no significant additional erosion would be expected during the 6 months remaining until the refueling outage. The repair will be performed as soon as l material is available, but no later than the next refueling outage.

l There are a total of six butterfly valves in the Service Water System which I are threttled, three on each of the two Service Water trains serving the l Control Building Air Conditioning System. A similar case of erosion / corrosion  !

occurred approximately two years ago on the "B" train. At that time, all of 1 the other locations were mapped using ultrasonics. It was realized at that time that a) the area in the pipe most affected by the turbulence created by the butterfly valves is located under the lap joint flange and b) the erosion / i corrosion mechanism results in small leaks indicating problems prior to '

significant structural damage to the piping. Currently, there are no inspec-tion techniques available (eddy current, ultrasonic or radiographic) which can detect the amount of erosion corrosion under the flange without disassembly of the flanged joint.

The piping downstream of the three velves on the opposite train ("A") will be inspected in the next two weeks by total disassembly of the flanges. These inspections have been prompted by an additional leak which occurred after the leak which is the subject of this relief request. This new leak will be evaluated and addressed in a future relief request.

The' piping downstream of one of the other two valves on the "B" train was replaced with Monel two years ago and is no longer subject to the failure mechanism seen here. The remaining "B" train location will be disassembled -

and inspected in the next month.

The results of these inspections and any required repairs will determine the schedule for future inspections.

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