ML20238C345

Forwards Response to NRC Request for Addl Info Re Accumulator Fill Line Nozzle Stress Calculation.Areas Discussed Include Estimate of Previous Nozzle Loading & Fatigue Usage Factors

ML20238C345
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	09/04/1987
From:	Cockfield D PORTLAND GENERAL ELECTRIC CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
TAC-65473, NUDOCS 8709100049
Download: ML20238C345 (3)

Text

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O M M W m W Genel~di Eledric Ocnigimiy David W. Cockfield ' Vice President, Nuclear September 4, 1987  !

Trojan Nuclear Plant Docket 50-344 License NPF-1 U.S. Nuc1 car Regulatory Commission ATTN: Document Control Desk Washington DC 20555

Dear Sir:

Accumulator Fill I.ine Failure Engineering Analyses On June 12, 1987, Portland Ceneral Electric Company (PGE) submitted dos-criptions and results of engineering analycos performsd as part of the evalcation cf the accumulator fill line failures. The Nucicar Regulatory Commicolon (NRC). Staff subsequently contacted PCE with questions about the accumulator fill'line nozzle stress calculation. The responses to these questions are provided in Attachment A.

Sincerely, e

Attachment c: Mr. John B. Martin Regional Administrator, Region V U.S. Nuclear Regulatory Commission Mr. R. C. Bar" NRC Resident Inspector Trojan Nucicar Plant

,Mr. David Kish, Director State of Oregon Department of Energy j 0

'9709100049 B70904 P p PDR ADOCK 05000344 PDR j k l p

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'121 SW Salmon Drmt Ft:tanct Oegon 97201

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- Trojen Nuclcir Plcnt Documint Control Dssk Dockst 50-344 S:ptembsr 4, 1987 Licence NPF-1 Attachment A Page 1 of 2 RESPONSES TO NRC REQUEST FOR ,

ADDITIONAL INFORMATION  !

A. Estimate of Previous Loading on Nozzle The estimate of the previous loading of the pipe and nozzle is depen-dent upon the assumed failure mechanism. The following mechanisms are possible:

1. Catastrophic failure produced by a load sufficiently large to cause failure with a single application. However, this is ruled out due  !

to the evidence of numerous crack striations as reported by the j metallurgical examination, which indicates fatigue failure.  !

2. Failure produced by a cyclic load sufficiently large to put the J entire section into plastic bending (the " plastic hinge"). How-ever, if failure had been due to plastic deformation, there should l have been some evidence of gross deformation (ovalization or necking) per Poisscu's ratio. The metallurgical examination did not report any such gross deformation.

3. Failure produced by a cyclic load taking the outermost fibers to j the elastic limit after clastic shakedown. The American Society of i Mecha01 cal Engineers (ASME) Code

• ures a bounding load between elastic'and plastic behavior, resulting in a stress range equal to j two times the yield stress. This type of progressive fatigue J failure (pre.e.eded by cycling leading to crack initiation) is 1 consistent with the metallurgical examination.

I B. Discussion of Fatigue Ucage Factors i l

Fatigue usage factors were csiculated for the nozzle in two locations.  !

The first location was at the bottom of thn socket and the second was at the base of the nozzle at the interface with the vessel weld. The usage factors were based on the estimated previous loading. A sensi-tivity check was performed using bending moments of double and of one- ,

half the estimated loading. The following summarizes the results.

Cycles to j Multiple of Failure at Pipe Nozzle Usage Factors Estimated Loading (le Usage = 1.0) At Socket At Base 1.0 2500 0.1 0.004 i 2.0 15 0.009 0.001 0.5 50,000 0.07 0.003 I

l NOTE: The reason that the usage factors are lower for the case of double-estimated loading is that the calculated stress l

l

Reference:

" Criteria of the ASME Bollor and Pressuro Vessel Codo for Design by Analysis Sections III and VIII, Division 2",

ASME, 1969.

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Trojan Nuclear Plant Document Control Desk Docket 50-344 September 4, 1987 License NPF-1 Attachment A Page 2 of 2 at the pipe almost doubles. When the stress intensity intensity range (Sn) goes into the plastic range, the Code requires the application of a magnification factor (Ke ) when calculating the alternating stress (Salt}'

This is to account for the shortened fatigue life and has the effect of reducing the number of cycles to failure (15 in this case). Because of the greater section modulii at I the nozzle socket and base, this does not apply to the ]

calculation of their cycles to failure. The effect is to make the usage factors go down for the socket and base.

The nozzle usage factors are well below the limit of 1.0. This is true regardless of the assumed estimated loading, and would be true (

for other assumed values of the yield stress. The usage factors aFe )

largely functions of the relative section properties of the pipe, -;,

socket, and nozzle. The sensitivity check using a moment two times. ci j the estimated loading bounds the possible effect of a plastic hinge' (the plastic hinge would result in a factor of approximately

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